feat: Add PathViewer and RiskDriftCard components with templates and styles

- Implemented PathViewerComponent for visualizing reachability call paths.
- Added RiskDriftCardComponent to display reachability drift results.
- Created corresponding HTML templates and SCSS styles for both components.
- Introduced test fixtures for reachability analysis in JSON format.
- Enhanced user interaction with collapsible and expandable features in PathViewer.
- Included risk trend visualization and summary metrics in RiskDriftCard.

src/Cli/StellaOps.Cli/Commands/CommandHandlers.Drift.cs

@@ -0,0 +1,320 @@
+// -----------------------------------------------------------------------------
+// CommandHandlers.Drift.cs
+// Sprint: SPRINT_3600_0004_0001_ui_evidence_chain
+// Tasks: UI-019, UI-020, UI-021
+// Description: Command handlers for reachability drift CLI.
+// -----------------------------------------------------------------------------
+
+using System.Text.Json;
+using Spectre.Console;
+
+namespace StellaOps.Cli.Commands;
+
+internal static partial class CommandHandlers
+{
+    private static readonly JsonSerializerOptions DriftJsonOptions = new()
+    {
+        WriteIndented = true,
+        PropertyNamingPolicy = JsonNamingPolicy.CamelCase
+    };
+
+    /// <summary>
+    /// Handler for `drift compare` command.
+    /// </summary>
+    internal static async Task HandleDriftCompareAsync(
+        IServiceProvider services,
+        string baseId,
+        string? headId,
+        string? image,
+        string? repo,
+        string output,
+        string minSeverity,
+        bool onlyIncreases,
+        bool verbose,
+        CancellationToken cancellationToken)
+    {
+        // TODO: Replace with actual service call when drift API is available
+        var console = AnsiConsole.Console;
+
+        if (verbose)
+        {
+            console.MarkupLine($"[dim]Comparing drift: base={baseId}, head={headId ?? "(latest)"}[/]");
+        }
+
+        // Placeholder: In real implementation, call drift service
+        var driftResult = new DriftResultDto
+        {
+            Id = Guid.NewGuid().ToString("N")[..8],
+            ComparedAt = DateTimeOffset.UtcNow.ToString("O"),
+            BaseGraphId = baseId,
+            HeadGraphId = headId ?? "latest",
+            Summary = new DriftSummaryDto
+            {
+                TotalSinks = 0,
+                IncreasedReachability = 0,
+                DecreasedReachability = 0,
+                UnchangedReachability = 0,
+                NewSinks = 0,
+                RemovedSinks = 0,
+                RiskTrend = "stable",
+                NetRiskDelta = 0
+            },
+            DriftedSinks = Array.Empty<DriftedSinkDto>()
+        };
+
+        switch (output)
+        {
+            case "json":
+                await WriteJsonOutputAsync(console, driftResult, cancellationToken);
+                break;
+            case "sarif":
+                await WriteSarifOutputAsync(console, driftResult, cancellationToken);
+                break;
+            default:
+                WriteTableOutput(console, driftResult, onlyIncreases, minSeverity);
+                break;
+        }
+    }
+
+    /// <summary>
+    /// Handler for `drift show` command.
+    /// </summary>
+    internal static async Task HandleDriftShowAsync(
+        IServiceProvider services,
+        string id,
+        string output,
+        bool expandPaths,
+        bool verbose,
+        CancellationToken cancellationToken)
+    {
+        var console = AnsiConsole.Console;
+
+        if (verbose)
+        {
+            console.MarkupLine($"[dim]Showing drift result: {id}[/]");
+        }
+
+        // Placeholder: In real implementation, call drift service
+        var driftResult = new DriftResultDto
+        {
+            Id = id,
+            ComparedAt = DateTimeOffset.UtcNow.ToString("O"),
+            BaseGraphId = "base",
+            HeadGraphId = "head",
+            Summary = new DriftSummaryDto
+            {
+                TotalSinks = 0,
+                IncreasedReachability = 0,
+                DecreasedReachability = 0,
+                UnchangedReachability = 0,
+                NewSinks = 0,
+                RemovedSinks = 0,
+                RiskTrend = "stable",
+                NetRiskDelta = 0
+            },
+            DriftedSinks = Array.Empty<DriftedSinkDto>()
+        };
+
+        switch (output)
+        {
+            case "json":
+                await WriteJsonOutputAsync(console, driftResult, cancellationToken);
+                break;
+            case "sarif":
+                await WriteSarifOutputAsync(console, driftResult, cancellationToken);
+                break;
+            default:
+                WriteTableOutput(console, driftResult, false, "info");
+                break;
+        }
+    }
+
+    // Task: UI-020 - Table output using Spectre.Console
+    private static void WriteTableOutput(
+        IAnsiConsole console,
+        DriftResultDto result,
+        bool onlyIncreases,
+        string minSeverity)
+    {
+        // Header panel
+        var header = new Panel(new Markup($"[bold]Reachability Drift[/] [dim]({result.Id})[/]"))
+            .Border(BoxBorder.Rounded)
+            .Padding(1, 0);
+        console.Write(header);
+
+        // Summary table
+        var summaryTable = new Table()
+            .Border(TableBorder.Rounded)
+            .AddColumn("Metric")
+            .AddColumn("Value");
+
+        summaryTable.AddRow("Trend", FormatTrend(result.Summary.RiskTrend));
+        summaryTable.AddRow("Net Risk Delta", FormatDelta(result.Summary.NetRiskDelta));
+        summaryTable.AddRow("Increased", result.Summary.IncreasedReachability.ToString());
+        summaryTable.AddRow("Decreased", result.Summary.DecreasedReachability.ToString());
+        summaryTable.AddRow("New Sinks", result.Summary.NewSinks.ToString());
+        summaryTable.AddRow("Removed Sinks", result.Summary.RemovedSinks.ToString());
+
+        console.Write(summaryTable);
+
+        // Sinks table
+        if (result.DriftedSinks.Length == 0)
+        {
+            console.MarkupLine("[green]No drifted sinks found.[/]");
+            return;
+        }
+
+        var sinksTable = new Table()
+            .Border(TableBorder.Rounded)
+            .AddColumn("Severity")
+            .AddColumn("Sink")
+            .AddColumn("CVE")
+            .AddColumn("Bucket Change")
+            .AddColumn("Delta");
+
+        var severityOrder = new Dictionary<string, int>
+        {
+            ["critical"] = 0,
+            ["high"] = 1,
+            ["medium"] = 2,
+            ["low"] = 3,
+            ["info"] = 4
+        };
+
+        var minSevOrder = severityOrder.GetValueOrDefault(minSeverity, 2);
+
+        foreach (var sink in result.DriftedSinks)
+        {
+            var sevOrder = severityOrder.GetValueOrDefault(sink.Severity ?? "info", 4);
+            if (sevOrder > minSevOrder) continue;
+            if (onlyIncreases && !sink.IsRiskIncrease) continue;
+
+            sinksTable.AddRow(
+                FormatSeverity(sink.Severity),
+                sink.SinkSymbol ?? "unknown",
+                sink.CveId ?? "-",
+                $"{sink.PreviousBucket ?? "N/A"} → {sink.CurrentBucket}",
+                FormatDelta(sink.RiskDelta));
+        }
+
+        console.Write(sinksTable);
+    }
+
+    // Task: UI-021 - JSON output
+    private static async Task WriteJsonOutputAsync(
+        IAnsiConsole console,
+        DriftResultDto result,
+        CancellationToken cancellationToken)
+    {
+        var json = JsonSerializer.Serialize(result, DriftJsonOptions);
+        console.WriteLine(json);
+        await Task.CompletedTask;
+    }
+
+    // Task: UI-022, UI-023 - SARIF output (placeholder)
+    private static async Task WriteSarifOutputAsync(
+        IAnsiConsole console,
+        DriftResultDto result,
+        CancellationToken cancellationToken)
+    {
+        // TODO: Implement full SARIF 2.1.0 generation in DriftSarifGenerator
+        var sarif = new
+        {
+            version = "2.1.0",
+            schema = "https://raw.githubusercontent.com/oasis-tcs/sarif-spec/master/Schemata/sarif-schema-2.1.0.json",
+            runs = new[]
+            {
+                new
+                {
+                    tool = new
+                    {
+                        driver = new
+                        {
+                            name = "StellaOps Drift",
+                            version = "1.0.0",
+                            informationUri = "https://stellaops.io/docs/drift"
+                        }
+                    },
+                    results = result.DriftedSinks.Select(sink => new
+                    {
+                        ruleId = sink.CveId ?? $"drift-{sink.SinkSymbol}",
+                        level = MapSeverityToSarif(sink.Severity),
+                        message = new
+                        {
+                            text = $"Reachability changed: {sink.PreviousBucket ?? "N/A"} → {sink.CurrentBucket}"
+                        },
+                        locations = Array.Empty<object>()
+                    }).ToArray()
+                }
+            }
+        };
+
+        var json = JsonSerializer.Serialize(sarif, DriftJsonOptions);
+        console.WriteLine(json);
+        await Task.CompletedTask;
+    }
+
+    private static string FormatTrend(string trend) => trend switch
+    {
+        "increasing" => "[red]↑ Increasing[/]",
+        "decreasing" => "[green]↓ Decreasing[/]",
+        _ => "[dim]→ Stable[/]"
+    };
+
+    private static string FormatDelta(int delta) => delta switch
+    {
+        > 0 => $"[red]+{delta}[/]",
+        < 0 => $"[green]{delta}[/]",
+        _ => "[dim]0[/]"
+    };
+
+    private static string FormatSeverity(string? severity) => severity switch
+    {
+        "critical" => "[white on red] CRITICAL [/]",
+        "high" => "[black on darkorange] HIGH [/]",
+        "medium" => "[black on yellow] MEDIUM [/]",
+        "low" => "[black on olive] LOW [/]",
+        _ => "[dim] INFO [/]"
+    };
+
+    private static string MapSeverityToSarif(string? severity) => severity switch
+    {
+        "critical" or "high" => "error",
+        "medium" => "warning",
+        _ => "note"
+    };
+
+    // DTOs for drift output
+    private sealed record DriftResultDto
+    {
+        public string Id { get; init; } = string.Empty;
+        public string ComparedAt { get; init; } = string.Empty;
+        public string BaseGraphId { get; init; } = string.Empty;
+        public string HeadGraphId { get; init; } = string.Empty;
+        public DriftSummaryDto Summary { get; init; } = new();
+        public DriftedSinkDto[] DriftedSinks { get; init; } = Array.Empty<DriftedSinkDto>();
+    }
+
+    private sealed record DriftSummaryDto
+    {
+        public int TotalSinks { get; init; }
+        public int IncreasedReachability { get; init; }
+        public int DecreasedReachability { get; init; }
+        public int UnchangedReachability { get; init; }
+        public int NewSinks { get; init; }
+        public int RemovedSinks { get; init; }
+        public string RiskTrend { get; init; } = "stable";
+        public int NetRiskDelta { get; init; }
+    }
+
+    private sealed record DriftedSinkDto
+    {
+        public string? SinkSymbol { get; init; }
+        public string? CveId { get; init; }
+        public string? Severity { get; init; }
+        public string? PreviousBucket { get; init; }
+        public string CurrentBucket { get; init; } = string.Empty;
+        public bool IsRiskIncrease { get; init; }
+        public int RiskDelta { get; init; }
+    }
+}

src/Cli/StellaOps.Cli/Commands/DriftCommandGroup.cs

@@ -0,0 +1,160 @@
+// -----------------------------------------------------------------------------
+// DriftCommandGroup.cs
+// Sprint: SPRINT_3600_0004_0001_ui_evidence_chain
+// Task: UI-019
+// Description: CLI command group for reachability drift detection.
+// -----------------------------------------------------------------------------
+
+using System.CommandLine;
+using Microsoft.Extensions.DependencyInjection;
+using StellaOps.Cli.Extensions;
+using Spectre.Console;
+
+namespace StellaOps.Cli.Commands;
+
+/// <summary>
+/// CLI command group for reachability drift detection.
+/// </summary>
+internal static class DriftCommandGroup
+{
+    internal static Command BuildDriftCommand(
+        IServiceProvider services,
+        Option<bool> verboseOption,
+        CancellationToken cancellationToken)
+    {
+        var drift = new Command("drift", "Reachability drift detection operations.");
+
+        drift.Add(BuildDriftCompareCommand(services, verboseOption, cancellationToken));
+        drift.Add(BuildDriftShowCommand(services, verboseOption, cancellationToken));
+
+        return drift;
+    }
+
+    private static Command BuildDriftCompareCommand(
+        IServiceProvider services,
+        Option<bool> verboseOption,
+        CancellationToken cancellationToken)
+    {
+        var baseOption = new Option<string>("--base", new[] { "-b" })
+        {
+            Description = "Base scan/graph ID or commit SHA for comparison.",
+            Required = true
+        };
+
+        var headOption = new Option<string>("--head", new[] { "-h" })
+        {
+            Description = "Head scan/graph ID or commit SHA for comparison (defaults to latest)."
+        };
+
+        var imageOption = new Option<string?>("--image", new[] { "-i" })
+        {
+            Description = "Container image reference (digest or tag)."
+        };
+
+        var repoOption = new Option<string?>("--repo", new[] { "-r" })
+        {
+            Description = "Repository reference (owner/repo)."
+        };
+
+        var outputOption = new Option<string>("--output", new[] { "-o" })
+        {
+            Description = "Output format: table (default), json, sarif."
+        }.SetDefaultValue("table").FromAmong("table", "json", "sarif");
+
+        var severityOption = new Option<string>("--min-severity")
+        {
+            Description = "Minimum severity to include: critical, high, medium, low, info."
+        }.SetDefaultValue("medium").FromAmong("critical", "high", "medium", "low", "info");
+
+        var onlyIncreasesOption = new Option<bool>("--only-increases")
+        {
+            Description = "Only show sinks with increased reachability (risk increases)."
+        };
+
+        var command = new Command("compare", "Compare reachability between two scans.")
+        {
+            baseOption,
+            headOption,
+            imageOption,
+            repoOption,
+            outputOption,
+            severityOption,
+            onlyIncreasesOption,
+            verboseOption
+        };
+
+        command.SetAction(parseResult =>
+        {
+            var baseId = parseResult.GetValue(baseOption)!;
+            var headId = parseResult.GetValue(headOption);
+            var image = parseResult.GetValue(imageOption);
+            var repo = parseResult.GetValue(repoOption);
+            var output = parseResult.GetValue(outputOption)!;
+            var minSeverity = parseResult.GetValue(severityOption)!;
+            var onlyIncreases = parseResult.GetValue(onlyIncreasesOption);
+            var verbose = parseResult.GetValue(verboseOption);
+
+            return CommandHandlers.HandleDriftCompareAsync(
+                services,
+                baseId,
+                headId,
+                image,
+                repo,
+                output,
+                minSeverity,
+                onlyIncreases,
+                verbose,
+                cancellationToken);
+        });
+
+        return command;
+    }
+
+    private static Command BuildDriftShowCommand(
+        IServiceProvider services,
+        Option<bool> verboseOption,
+        CancellationToken cancellationToken)
+    {
+        var idOption = new Option<string>("--id")
+        {
+            Description = "Drift result ID to display.",
+            Required = true
+        };
+
+        var outputOption = new Option<string>("--output", new[] { "-o" })
+        {
+            Description = "Output format: table (default), json, sarif."
+        }.SetDefaultValue("table").FromAmong("table", "json", "sarif");
+
+        var expandPathsOption = new Option<bool>("--expand-paths")
+        {
+            Description = "Show full call paths instead of compressed view."
+        };
+
+        var command = new Command("show", "Show details of a drift result.")
+        {
+            idOption,
+            outputOption,
+            expandPathsOption,
+            verboseOption
+        };
+
+        command.SetAction(parseResult =>
+        {
+            var id = parseResult.GetValue(idOption)!;
+            var output = parseResult.GetValue(outputOption)!;
+            var expandPaths = parseResult.GetValue(expandPathsOption);
+            var verbose = parseResult.GetValue(verboseOption);
+
+            return CommandHandlers.HandleDriftShowAsync(
+                services,
+                id,
+                output,
+                expandPaths,
+                verbose,
+                cancellationToken);
+        });
+
+        return command;
+    }
+}

src/Scanner/StellaOps.Scanner.Worker/Processing/EpssEnrichmentJob.cs

@@ -0,0 +1,384 @@
+// -----------------------------------------------------------------------------
+// EpssEnrichmentJob.cs
+// Sprint: SPRINT_3413_0001_0001_epss_live_enrichment
+// Task: Task #1 - Implement EpssEnrichmentJob service
+// Description: Background job that enriches vulnerability instances with current EPSS scores.
+// -----------------------------------------------------------------------------
+
+using System.Diagnostics;
+using Microsoft.Extensions.Hosting;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Options;
+using StellaOps.Scanner.Core.Epss;
+using StellaOps.Scanner.Storage.Epss;
+using StellaOps.Scanner.Storage.Repositories;
+
+namespace StellaOps.Scanner.Worker.Processing;
+
+/// <summary>
+/// Options for the EPSS enrichment job.
+/// </summary>
+public sealed class EpssEnrichmentOptions
+{
+    /// <summary>
+    /// Configuration section name.
+    /// </summary>
+    public const string SectionName = "Epss:Enrichment";
+
+    /// <summary>
+    /// Whether the enrichment job is enabled. Default: true.
+    /// </summary>
+    public bool Enabled { get; set; } = true;
+
+    /// <summary>
+    /// Delay after EPSS ingestion before running enrichment. Default: 1 minute.
+    /// </summary>
+    public TimeSpan PostIngestDelay { get; set; } = TimeSpan.FromMinutes(1);
+
+    /// <summary>
+    /// Batch size for processing vulnerability instances. Default: 1000.
+    /// </summary>
+    public int BatchSize { get; set; } = 1000;
+
+    /// <summary>
+    /// High percentile threshold. Scores at or above this trigger CROSSED_HIGH. Default: 0.99.
+    /// </summary>
+    public double HighPercentile { get; set; } = 0.99;
+
+    /// <summary>
+    /// High score threshold. Scores at or above this trigger priority elevation. Default: 0.5.
+    /// </summary>
+    public double HighScore { get; set; } = 0.5;
+
+    /// <summary>
+    /// Big jump delta threshold. Score changes >= this trigger BIG_JUMP flag. Default: 0.10.
+    /// </summary>
+    public double BigJumpDelta { get; set; } = 0.10;
+
+    /// <summary>
+    /// Critical percentile threshold. Default: 0.995 (top 0.5%).
+    /// </summary>
+    public double CriticalPercentile { get; set; } = 0.995;
+
+    /// <summary>
+    /// Medium percentile threshold. Default: 0.90 (top 10%).
+    /// </summary>
+    public double MediumPercentile { get; set; } = 0.90;
+
+    /// <summary>
+    /// Process only CVEs with specific change flags. Empty = process all.
+    /// </summary>
+    public EpssChangeFlags FlagsToProcess { get; set; } =
+        EpssChangeFlags.NewScored |
+        EpssChangeFlags.CrossedHigh |
+        EpssChangeFlags.BigJumpUp |
+        EpssChangeFlags.BigJumpDown;
+
+    /// <summary>
+    /// Suppress signals on model version change. Default: true.
+    /// </summary>
+    public bool SuppressSignalsOnModelChange { get; set; } = true;
+}
+
+/// <summary>
+/// Background service that enriches vulnerability instances with current EPSS scores.
+/// Runs after EPSS ingestion to update existing findings with new priority bands.
+/// </summary>
+public sealed class EpssEnrichmentJob : BackgroundService
+{
+    private readonly IEpssRepository _epssRepository;
+    private readonly IEpssProvider _epssProvider;
+    private readonly IEpssSignalPublisher _signalPublisher;
+    private readonly IOptions<EpssEnrichmentOptions> _options;
+    private readonly TimeProvider _timeProvider;
+    private readonly ILogger<EpssEnrichmentJob> _logger;
+    private readonly ActivitySource _activitySource = new("StellaOps.Scanner.EpssEnrichment");
+
+    // Event to trigger enrichment after ingestion
+    private readonly SemaphoreSlim _enrichmentTrigger = new(0);
+
+    public EpssEnrichmentJob(
+        IEpssRepository epssRepository,
+        IEpssProvider epssProvider,
+        IEpssSignalPublisher signalPublisher,
+        IOptions<EpssEnrichmentOptions> options,
+        TimeProvider timeProvider,
+        ILogger<EpssEnrichmentJob> logger)
+    {
+        _epssRepository = epssRepository ?? throw new ArgumentNullException(nameof(epssRepository));
+        _epssProvider = epssProvider ?? throw new ArgumentNullException(nameof(epssProvider));
+        _signalPublisher = signalPublisher ?? throw new ArgumentNullException(nameof(signalPublisher));
+        _options = options ?? throw new ArgumentNullException(nameof(options));
+        _timeProvider = timeProvider ?? throw new ArgumentNullException(nameof(timeProvider));
+        _logger = logger ?? throw new ArgumentNullException(nameof(logger));
+    }
+
+    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
+    {
+        _logger.LogInformation("EPSS enrichment job started");
+
+        var opts = _options.Value;
+
+        if (!opts.Enabled)
+        {
+            _logger.LogInformation("EPSS enrichment job is disabled");
+            return;
+        }
+
+        while (!stoppingToken.IsCancellationRequested)
+        {
+            try
+            {
+                // Wait for enrichment trigger or cancellation
+                await _enrichmentTrigger.WaitAsync(stoppingToken);
+
+                // Add delay after ingestion to ensure data is fully committed
+                await Task.Delay(opts.PostIngestDelay, stoppingToken);
+
+                await EnrichAsync(stoppingToken);
+            }
+            catch (OperationCanceledException) when (stoppingToken.IsCancellationRequested)
+            {
+                break;
+            }
+            catch (Exception ex)
+            {
+                _logger.LogError(ex, "EPSS enrichment job encountered an error");
+            }
+        }
+
+        _logger.LogInformation("EPSS enrichment job stopped");
+    }
+
+    /// <summary>
+    /// Triggers the enrichment process. Called after EPSS data is ingested.
+    /// </summary>
+    public void TriggerEnrichment()
+    {
+        _enrichmentTrigger.Release();
+        _logger.LogDebug("EPSS enrichment triggered");
+    }
+
+    /// <summary>
+    /// Runs the enrichment process. Updates vulnerability instances with current EPSS scores.
+    /// </summary>
+    public async Task EnrichAsync(CancellationToken cancellationToken = default)
+    {
+        using var activity = _activitySource.StartActivity("epss.enrich", ActivityKind.Internal);
+        var stopwatch = Stopwatch.StartNew();
+        var opts = _options.Value;
+
+        _logger.LogInformation("Starting EPSS enrichment");
+
+        try
+        {
+            // Get the latest model date
+            var modelDate = await _epssProvider.GetLatestModelDateAsync(cancellationToken);
+            if (!modelDate.HasValue)
+            {
+                _logger.LogWarning("No EPSS data available for enrichment");
+                return;
+            }
+
+            activity?.SetTag("epss.model_date", modelDate.Value.ToString("yyyy-MM-dd"));
+            _logger.LogDebug("Using EPSS model date: {ModelDate}", modelDate.Value);
+
+            // Get CVEs with changes that need processing
+            var changedCves = await GetChangedCvesAsync(modelDate.Value, opts.FlagsToProcess, cancellationToken);
+
+            if (changedCves.Count == 0)
+            {
+                _logger.LogDebug("No CVE changes to process");
+                return;
+            }
+
+            _logger.LogInformation("Processing {Count} CVEs with EPSS changes", changedCves.Count);
+            activity?.SetTag("epss.changed_cve_count", changedCves.Count);
+
+            var totalUpdated = 0;
+            var totalBandChanges = 0;
+
+            // Process in batches
+            foreach (var batch in changedCves.Chunk(opts.BatchSize))
+            {
+                var (updated, bandChanges) = await ProcessBatchAsync(
+                    batch,
+                    modelDate.Value,
+                    cancellationToken);
+
+                totalUpdated += updated;
+                totalBandChanges += bandChanges;
+            }
+
+            stopwatch.Stop();
+
+            _logger.LogInformation(
+                "EPSS enrichment completed: updated={Updated}, bandChanges={BandChanges}, duration={Duration}ms",
+                totalUpdated,
+                totalBandChanges,
+                stopwatch.ElapsedMilliseconds);
+
+            activity?.SetTag("epss.updated_count", totalUpdated);
+            activity?.SetTag("epss.band_change_count", totalBandChanges);
+            activity?.SetTag("epss.duration_ms", stopwatch.ElapsedMilliseconds);
+        }
+        catch (Exception ex)
+        {
+            _logger.LogError(ex, "EPSS enrichment failed");
+            activity?.SetStatus(ActivityStatusCode.Error, ex.Message);
+            throw;
+        }
+    }
+
+    private async Task<IReadOnlyList<EpssChangeRecord>> GetChangedCvesAsync(
+        DateOnly modelDate,
+        EpssChangeFlags flags,
+        CancellationToken cancellationToken)
+    {
+        // Query epss_changes table for CVEs with matching flags for the model date (Task #4)
+        _logger.LogDebug("Querying EPSS changes for model date {ModelDate} with flags {Flags}", modelDate, flags);
+
+        var changes = await _epssRepository.GetChangesAsync(modelDate, flags, cancellationToken: cancellationToken);
+
+        _logger.LogDebug("Found {Count} EPSS changes matching flags {Flags}", changes.Count, flags);
+
+        return changes;
+    }
+
+    private async Task<(int Updated, int BandChanges)> ProcessBatchAsync(
+        EpssChangeRecord[] batch,
+        DateOnly modelDate,
+        CancellationToken cancellationToken)
+    {
+        var opts = _options.Value;
+        var updated = 0;
+        var bandChanges = 0;
+
+        // Get current EPSS scores for all CVEs in batch
+        var cveIds = batch.Select(c => c.CveId).ToList();
+        var epssResult = await _epssProvider.GetCurrentBatchAsync(cveIds, cancellationToken);
+
+        foreach (var change in batch)
+        {
+            var evidence = epssResult.Found.FirstOrDefault(e =>
+                string.Equals(e.CveId, change.CveId, StringComparison.OrdinalIgnoreCase));
+
+            if (evidence is null)
+            {
+                continue;
+            }
+
+            var previousBand = change.PreviousBand;
+            var newBand = ComputePriorityBand(evidence.Percentile, opts);
+
+            // Check if band changed
+            if (previousBand != newBand)
+            {
+                bandChanges++;
+
+                // Emit vuln.priority.changed event
+                await EmitPriorityChangedEventAsync(
+                    change.CveId,
+                    previousBand,
+                    newBand,
+                    evidence,
+                    cancellationToken);
+            }
+
+            updated++;
+        }
+
+        return (updated, bandChanges);
+    }
+
+    private static EpssPriorityBand ComputePriorityBand(double percentile, EpssEnrichmentOptions opts)
+    {
+        if (percentile >= opts.CriticalPercentile)
+        {
+            return EpssPriorityBand.Critical;
+        }
+
+        if (percentile >= opts.HighPercentile)
+        {
+            return EpssPriorityBand.High;
+        }
+
+        if (percentile >= opts.MediumPercentile)
+        {
+            return EpssPriorityBand.Medium;
+        }
+
+        return EpssPriorityBand.Low;
+    }
+
+    private Task EmitPriorityChangedEventAsync(
+        string cveId,
+        EpssPriorityBand previousBand,
+        EpssPriorityBand newBand,
+        EpssEvidence evidence,
+        CancellationToken cancellationToken)
+    {
+        // Task #6: Emit `vuln.priority.changed` event via signal publisher
+        _logger.LogDebug(
+            "Priority changed: {CveId} {PreviousBand} -> {NewBand} (score={Score:F4}, percentile={Percentile:F4})",
+            cveId,
+            previousBand,
+            newBand,
+            evidence.Score,
+            evidence.Percentile);
+
+        // Publish priority changed event (Task #6)
+        var result = await _signalPublisher.PublishPriorityChangedAsync(
+            Guid.Empty, // Tenant ID would come from context
+            cveId,
+            previousBand.ToString(),
+            newBand.ToString(),
+            evidence.Score,
+            evidence.ModelDate,
+            cancellationToken);
+
+        if (!result.Success)
+        {
+            _logger.LogWarning(
+                "Failed to publish priority changed event for {CveId}: {Error}",
+                cveId,
+                result.Error);
+        }
+    }
+}
+
+/// <summary>
+/// Record representing an EPSS change that needs processing.
+/// </summary>
+public sealed record EpssChangeRecord
+{
+    /// <summary>
+    /// CVE identifier.
+    /// </summary>
+    public required string CveId { get; init; }
+
+    /// <summary>
+    /// Change flags indicating what changed.
+    /// </summary>
+    public EpssChangeFlags Flags { get; init; }
+
+    /// <summary>
+    /// Previous EPSS score (if available).
+    /// </summary>
+    public double? PreviousScore { get; init; }
+
+    /// <summary>
+    /// New EPSS score.
+    /// </summary>
+    public double NewScore { get; init; }
+
+    /// <summary>
+    /// Previous priority band (if available).
+    /// </summary>
+    public EpssPriorityBand PreviousBand { get; init; }
+
+    /// <summary>
+    /// Model date for this change.
+    /// </summary>
+    public DateOnly ModelDate { get; init; }
+}

src/Scanner/StellaOps.Scanner.Worker/Processing/EpssEnrichmentStageExecutor.cs

@@ -0,0 +1,205 @@
+// -----------------------------------------------------------------------------
+// EpssEnrichmentStageExecutor.cs
+// Sprint: SPRINT_3410_0002_0001_epss_scanner_integration
+// Task: EPSS-SCAN-006
+// Description: Scan stage executor that enriches findings with EPSS scores.
+// -----------------------------------------------------------------------------
+
+using Microsoft.Extensions.Logging;
+using StellaOps.Scanner.Core.Contracts;
+using StellaOps.Scanner.Core.Epss;
+
+namespace StellaOps.Scanner.Worker.Processing;
+
+/// <summary>
+/// Scan stage executor that enriches vulnerability findings with EPSS scores.
+/// Attaches immutable EPSS evidence to each CVE at scan time.
+/// </summary>
+public sealed class EpssEnrichmentStageExecutor : IScanStageExecutor
+{
+    private readonly IEpssProvider _epssProvider;
+    private readonly ILogger<EpssEnrichmentStageExecutor> _logger;
+
+    public EpssEnrichmentStageExecutor(
+        IEpssProvider epssProvider,
+        ILogger<EpssEnrichmentStageExecutor> logger)
+    {
+        _epssProvider = epssProvider ?? throw new ArgumentNullException(nameof(epssProvider));
+        _logger = logger ?? throw new ArgumentNullException(nameof(logger));
+    }
+
+    public string StageName => ScanStageNames.EpssEnrichment;
+
+    public async ValueTask ExecuteAsync(ScanJobContext context, CancellationToken cancellationToken)
+    {
+        ArgumentNullException.ThrowIfNull(context);
+
+        // Check if EPSS data is available
+        var isAvailable = await _epssProvider.IsAvailableAsync(cancellationToken).ConfigureAwait(false);
+        if (!isAvailable)
+        {
+            _logger.LogWarning("EPSS data not available; skipping EPSS enrichment for job {JobId}", context.JobId);
+            return;
+        }
+
+        // Get CVE IDs from findings
+        var cveIds = ExtractCveIds(context);
+        if (cveIds.Count == 0)
+        {
+            _logger.LogDebug("No CVE IDs found in findings for job {JobId}; skipping EPSS enrichment", context.JobId);
+            return;
+        }
+
+        _logger.LogInformation(
+            "Enriching {CveCount} CVEs with EPSS scores for job {JobId}",
+            cveIds.Count,
+            context.JobId);
+
+        // Fetch EPSS scores in batch
+        var epssResult = await _epssProvider.GetCurrentBatchAsync(cveIds, cancellationToken).ConfigureAwait(false);
+
+        _logger.LogDebug(
+            "EPSS lookup: found={Found}, notFound={NotFound}, timeMs={TimeMs}, fromCache={FromCache}",
+            epssResult.Found.Count,
+            epssResult.NotFound.Count,
+            epssResult.LookupTimeMs,
+            epssResult.PartiallyFromCache);
+
+        // Store EPSS evidence in analysis context
+        var epssMap = epssResult.Found.ToDictionary(
+            e => e.CveId,
+            e => e,
+            StringComparer.OrdinalIgnoreCase);
+
+        context.Analysis.Set(ScanAnalysisKeys.EpssEvidence, epssMap);
+        context.Analysis.Set(ScanAnalysisKeys.EpssModelDate, epssResult.ModelDate);
+        context.Analysis.Set(ScanAnalysisKeys.EpssNotFoundCves, epssResult.NotFound.ToList());
+
+        _logger.LogInformation(
+            "EPSS enrichment completed for job {JobId}: {Found}/{Total} CVEs enriched, model date {ModelDate}",
+            context.JobId,
+            epssMap.Count,
+            cveIds.Count,
+            epssResult.ModelDate);
+    }
+
+    private static HashSet<string> ExtractCveIds(ScanJobContext context)
+    {
+        var cveIds = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
+
+        // Extract from OS package analyzer results
+        if (context.Analysis.TryGet<Dictionary<string, object>>(ScanAnalysisKeys.OsPackageAnalyzers, out var osResults) && osResults is not null)
+        {
+            foreach (var analyzerResult in osResults.Values)
+            {
+                ExtractCvesFromAnalyzerResult(analyzerResult, cveIds);
+            }
+        }
+
+        // Extract from language analyzer results
+        if (context.Analysis.TryGet<Dictionary<string, object>>(ScanAnalysisKeys.LanguagePackageAnalyzers, out var langResults) && langResults is not null)
+        {
+            foreach (var analyzerResult in langResults.Values)
+            {
+                ExtractCvesFromAnalyzerResult(analyzerResult, cveIds);
+            }
+        }
+
+        // Extract from consolidated findings if available
+        if (context.Analysis.TryGet<IEnumerable<object>>(ScanAnalysisKeys.ConsolidatedFindings, out var findings) && findings is not null)
+        {
+            foreach (var finding in findings)
+            {
+                ExtractCvesFromFinding(finding, cveIds);
+            }
+        }
+
+        return cveIds;
+    }
+
+    private static void ExtractCvesFromAnalyzerResult(object analyzerResult, HashSet<string> cveIds)
+    {
+        // Use reflection to extract CVE IDs from various analyzer result types
+        // This handles OSPackageAnalyzerResult, LanguagePackageAnalyzerResult, etc.
+        var resultType = analyzerResult.GetType();
+
+        // Try to get Vulnerabilities property
+        var vulnsProperty = resultType.GetProperty("Vulnerabilities");
+        if (vulnsProperty?.GetValue(analyzerResult) is IEnumerable<object> vulns)
+        {
+            foreach (var vuln in vulns)
+            {
+                ExtractCvesFromFinding(vuln, cveIds);
+            }
+        }
+
+        // Try to get Findings property
+        var findingsProperty = resultType.GetProperty("Findings");
+        if (findingsProperty?.GetValue(analyzerResult) is IEnumerable<object> findingsList)
+        {
+            foreach (var finding in findingsList)
+            {
+                ExtractCvesFromFinding(finding, cveIds);
+            }
+        }
+    }
+
+    private static void ExtractCvesFromFinding(object finding, HashSet<string> cveIds)
+    {
+        var findingType = finding.GetType();
+
+        // Try CveId property
+        var cveIdProperty = findingType.GetProperty("CveId");
+        if (cveIdProperty?.GetValue(finding) is string cveId && !string.IsNullOrWhiteSpace(cveId))
+        {
+            cveIds.Add(cveId);
+            return;
+        }
+
+        // Try VulnerabilityId property (some findings use this)
+        var vulnIdProperty = findingType.GetProperty("VulnerabilityId");
+        if (vulnIdProperty?.GetValue(finding) is string vulnId &&
+            !string.IsNullOrWhiteSpace(vulnId) &&
+            vulnId.StartsWith("CVE-", StringComparison.OrdinalIgnoreCase))
+        {
+            cveIds.Add(vulnId);
+            return;
+        }
+
+        // Try Identifiers collection
+        var identifiersProperty = findingType.GetProperty("Identifiers");
+        if (identifiersProperty?.GetValue(finding) is IEnumerable<object> identifiers)
+        {
+            foreach (var identifier in identifiers)
+            {
+                var idValue = identifier.ToString();
+                if (!string.IsNullOrWhiteSpace(idValue) &&
+                    idValue.StartsWith("CVE-", StringComparison.OrdinalIgnoreCase))
+                {
+                    cveIds.Add(idValue);
+                }
+            }
+        }
+    }
+}
+
+/// <summary>
+/// Well-known keys for EPSS-related analysis data.
+/// </summary>
+public static partial class ScanAnalysisKeys
+{
+    /// <summary>
+    /// Dictionary of CVE ID to EpssEvidence for enriched findings.
+    /// </summary>
+    public const string EpssEvidence = "epss.evidence";
+
+    /// <summary>
+    /// The EPSS model date used for enrichment.
+    /// </summary>
+    public const string EpssModelDate = "epss.model_date";
+
+    /// <summary>
+    /// List of CVE IDs that were not found in EPSS data.
+    /// </summary>
+    public const string EpssNotFoundCves = "epss.not_found";
+}

src/Scanner/StellaOps.Scanner.Worker/Processing/EpssIngestJob.cs

@@ -67,6 +67,7 @@ public sealed class EpssIngestOptions
 public sealed class EpssIngestJob : BackgroundService
 {
     private readonly IEpssRepository _repository;
+    private readonly IEpssRawRepository? _rawRepository;
     private readonly EpssOnlineSource _onlineSource;
     private readonly EpssBundleSource _bundleSource;
     private readonly EpssCsvStreamParser _parser;
@@ -82,9 +83,11 @@ public sealed class EpssIngestJob : BackgroundService
         EpssCsvStreamParser parser,
         IOptions<EpssIngestOptions> options,
         TimeProvider timeProvider,
-        ILogger<EpssIngestJob> logger)
+        ILogger<EpssIngestJob> logger,
+        IEpssRawRepository? rawRepository = null)
     {
         _repository = repository ?? throw new ArgumentNullException(nameof(repository));
+        _rawRepository = rawRepository; // Optional - raw storage for replay capability
         _onlineSource = onlineSource ?? throw new ArgumentNullException(nameof(onlineSource));
         _bundleSource = bundleSource ?? throw new ArgumentNullException(nameof(bundleSource));
         _parser = parser ?? throw new ArgumentNullException(nameof(parser));
@@ -186,6 +189,18 @@ public sealed class EpssIngestJob : BackgroundService
                     session,
                     cancellationToken).ConfigureAwait(false);
 
+                // Store raw payload for replay capability (Sprint: SPRINT_3413_0001_0001, Task: R2)
+                if (_rawRepository is not null)
+                {
+                    await StoreRawPayloadAsync(
+                        importRun.ImportRunId,
+                        sourceFile.SourceUri,
+                        modelDate,
+                        session,
+                        fileContent.Length,
+                        cancellationToken).ConfigureAwait(false);
+                }
+
                 // Mark success
                 await _repository.MarkImportSucceededAsync(
                     importRun.ImportRunId,
@@ -279,4 +294,69 @@ public sealed class EpssIngestJob : BackgroundService
         var hash = System.Security.Cryptography.SHA256.HashData(content);
         return Convert.ToHexString(hash).ToLowerInvariant();
     }
+
+    /// <summary>
+    /// Stores raw EPSS payload for deterministic replay capability.
+    /// Sprint: SPRINT_3413_0001_0001, Task: R2
+    /// </summary>
+    private async Task StoreRawPayloadAsync(
+        Guid importRunId,
+        string sourceUri,
+        DateOnly modelDate,
+        EpssParsedSession session,
+        long compressedSize,
+        CancellationToken cancellationToken)
+    {
+        if (_rawRepository is null)
+        {
+            return;
+        }
+
+        try
+        {
+            // Convert parsed rows to JSON array for raw storage
+            var payload = System.Text.Json.JsonSerializer.Serialize(
+                session.Rows.Select(r => new
+                {
+                    cve = r.CveId,
+                    epss = r.Score,
+                    percentile = r.Percentile
+                }),
+                new System.Text.Json.JsonSerializerOptions { WriteIndented = false });
+
+            var payloadBytes = System.Text.Encoding.UTF8.GetBytes(payload);
+            var payloadSha256 = System.Security.Cryptography.SHA256.HashData(payloadBytes);
+
+            var raw = new EpssRaw
+            {
+                SourceUri = sourceUri,
+                AsOfDate = modelDate,
+                Payload = payload,
+                PayloadSha256 = payloadSha256,
+                HeaderComment = session.HeaderComment,
+                ModelVersion = session.ModelVersionTag,
+                PublishedDate = session.PublishedDate,
+                RowCount = session.RowCount,
+                CompressedSize = compressedSize,
+                DecompressedSize = payloadBytes.LongLength,
+                ImportRunId = importRunId
+            };
+
+            await _rawRepository.CreateAsync(raw, cancellationToken).ConfigureAwait(false);
+
+            _logger.LogDebug(
+                "Stored raw EPSS payload: modelDate={ModelDate}, rows={RowCount}, size={Size}",
+                modelDate,
+                session.RowCount,
+                payloadBytes.Length);
+        }
+        catch (Exception ex)
+        {
+            // Log but don't fail ingestion if raw storage fails
+            _logger.LogWarning(
+                ex,
+                "Failed to store raw EPSS payload for {ModelDate}; ingestion will continue",
+                modelDate);
+        }
+    }
 }

src/Scanner/StellaOps.Scanner.Worker/Processing/EpssSignalJob.cs

@@ -0,0 +1,505 @@
+// -----------------------------------------------------------------------------
+// EpssSignalJob.cs
+// Sprint: SPRINT_3413_0001_0001_epss_live_enrichment
+// Tasks: S5-S10 - Signal generation service
+// Description: Background job that generates tenant-scoped EPSS signals.
+// -----------------------------------------------------------------------------
+
+using System.Diagnostics;
+using System.Text.Json;
+using Microsoft.Extensions.Hosting;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Options;
+using StellaOps.Scanner.Core.Epss;
+using StellaOps.Scanner.Storage.Epss;
+using StellaOps.Scanner.Storage.Repositories;
+
+namespace StellaOps.Scanner.Worker.Processing;
+
+/// <summary>
+/// Options for the EPSS signal generation job.
+/// </summary>
+public sealed class EpssSignalOptions
+{
+    /// <summary>
+    /// Configuration section name.
+    /// </summary>
+    public const string SectionName = "Epss:Signal";
+
+    /// <summary>
+    /// Whether the signal job is enabled. Default: true.
+    /// </summary>
+    public bool Enabled { get; set; } = true;
+
+    /// <summary>
+    /// Delay after enrichment before generating signals. Default: 30 seconds.
+    /// </summary>
+    public TimeSpan PostEnrichmentDelay { get; set; } = TimeSpan.FromSeconds(30);
+
+    /// <summary>
+    /// Batch size for signal generation. Default: 500.
+    /// </summary>
+    public int BatchSize { get; set; } = 500;
+
+    /// <summary>
+    /// Signal retention days. Default: 90.
+    /// </summary>
+    public int RetentionDays { get; set; } = 90;
+}
+
+/// <summary>
+/// EPSS signal event types.
+/// </summary>
+public static class EpssSignalEventTypes
+{
+    /// <summary>
+    /// Significant score increase (delta >= threshold).
+    /// </summary>
+    public const string RiskSpike = "RISK_SPIKE";
+
+    /// <summary>
+    /// Priority band change (e.g., MEDIUM -> HIGH).
+    /// </summary>
+    public const string BandChange = "BAND_CHANGE";
+
+    /// <summary>
+    /// New CVE scored for the first time.
+    /// </summary>
+    public const string NewHigh = "NEW_HIGH";
+
+    /// <summary>
+    /// CVE dropped from HIGH/CRITICAL to LOW.
+    /// </summary>
+    public const string DroppedLow = "DROPPED_LOW";
+
+    /// <summary>
+    /// EPSS model version changed (summary event).
+    /// </summary>
+    public const string ModelUpdated = "MODEL_UPDATED";
+}
+
+/// <summary>
+/// Background service that generates tenant-scoped EPSS signals.
+/// Only generates signals for CVEs that are observed in tenant's inventory.
+/// </summary>
+public sealed class EpssSignalJob : BackgroundService
+{
+    private readonly IEpssRepository _epssRepository;
+    private readonly IEpssSignalRepository _signalRepository;
+    private readonly IObservedCveRepository _observedCveRepository;
+    private readonly IEpssSignalPublisher _signalPublisher;
+    private readonly IEpssProvider _epssProvider;
+    private readonly IOptions<EpssSignalOptions> _options;
+    private readonly TimeProvider _timeProvider;
+    private readonly ILogger<EpssSignalJob> _logger;
+    private readonly ActivitySource _activitySource = new("StellaOps.Scanner.EpssSignal");
+
+    // Trigger for signal generation
+    private readonly SemaphoreSlim _signalTrigger = new(0);
+
+    // Track last processed model date to detect version changes
+    private string? _lastModelVersion;
+
+    public EpssSignalJob(
+        IEpssRepository epssRepository,
+        IEpssSignalRepository signalRepository,
+        IObservedCveRepository observedCveRepository,
+        IEpssSignalPublisher signalPublisher,
+        IEpssProvider epssProvider,
+        IOptions<EpssSignalOptions> options,
+        TimeProvider timeProvider,
+        ILogger<EpssSignalJob> logger)
+    {
+        _epssRepository = epssRepository ?? throw new ArgumentNullException(nameof(epssRepository));
+        _signalRepository = signalRepository ?? throw new ArgumentNullException(nameof(signalRepository));
+        _observedCveRepository = observedCveRepository ?? throw new ArgumentNullException(nameof(observedCveRepository));
+        _signalPublisher = signalPublisher ?? throw new ArgumentNullException(nameof(signalPublisher));
+        _epssProvider = epssProvider ?? throw new ArgumentNullException(nameof(epssProvider));
+        _options = options ?? throw new ArgumentNullException(nameof(options));
+        _timeProvider = timeProvider ?? throw new ArgumentNullException(nameof(timeProvider));
+        _logger = logger ?? throw new ArgumentNullException(nameof(logger));
+    }
+
+    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
+    {
+        _logger.LogInformation("EPSS signal job started");
+
+        var opts = _options.Value;
+
+        if (!opts.Enabled)
+        {
+            _logger.LogInformation("EPSS signal job is disabled");
+            return;
+        }
+
+        while (!stoppingToken.IsCancellationRequested)
+        {
+            try
+            {
+                // Wait for signal trigger or cancellation
+                await _signalTrigger.WaitAsync(stoppingToken);
+
+                // Add delay after enrichment to ensure data consistency
+                await Task.Delay(opts.PostEnrichmentDelay, stoppingToken);
+
+                await GenerateSignalsAsync(stoppingToken);
+
+                // Periodic pruning of old signals
+                await _signalRepository.PruneAsync(opts.RetentionDays, stoppingToken);
+            }
+            catch (OperationCanceledException) when (stoppingToken.IsCancellationRequested)
+            {
+                break;
+            }
+            catch (Exception ex)
+            {
+                _logger.LogError(ex, "EPSS signal job encountered an error");
+            }
+        }
+
+        _logger.LogInformation("EPSS signal job stopped");
+    }
+
+    /// <summary>
+    /// Triggers signal generation. Called after EPSS enrichment completes.
+    /// </summary>
+    public void TriggerSignalGeneration()
+    {
+        _signalTrigger.Release();
+        _logger.LogDebug("EPSS signal generation triggered");
+    }
+
+    /// <summary>
+    /// Generates signals for all tenants based on EPSS changes.
+    /// </summary>
+    public async Task GenerateSignalsAsync(CancellationToken cancellationToken = default)
+    {
+        using var activity = _activitySource.StartActivity("epss.signal.generate", ActivityKind.Internal);
+        var stopwatch = Stopwatch.StartNew();
+        var opts = _options.Value;
+
+        _logger.LogInformation("Starting EPSS signal generation");
+
+        try
+        {
+            // Get current model date
+            var modelDate = await _epssProvider.GetLatestModelDateAsync(cancellationToken);
+            if (!modelDate.HasValue)
+            {
+                _logger.LogWarning("No EPSS data available for signal generation");
+                return;
+            }
+
+            activity?.SetTag("epss.model_date", modelDate.Value.ToString("yyyy-MM-dd"));
+
+            // Check for model version change (S7)
+            var currentModelVersion = await GetCurrentModelVersionAsync(modelDate.Value, cancellationToken);
+            var isModelChange = _lastModelVersion is not null &&
+                                !string.Equals(_lastModelVersion, currentModelVersion, StringComparison.Ordinal);
+
+            if (isModelChange)
+            {
+                _logger.LogInformation(
+                    "EPSS model version changed: {OldVersion} -> {NewVersion}",
+                    _lastModelVersion,
+                    currentModelVersion);
+            }
+
+            _lastModelVersion = currentModelVersion;
+
+            // Get changes from epss_changes table
+            var changes = await GetEpssChangesAsync(modelDate.Value, cancellationToken);
+            if (changes.Count == 0)
+            {
+                _logger.LogDebug("No EPSS changes to process for signals");
+                return;
+            }
+
+            _logger.LogInformation("Processing {Count} EPSS changes for signal generation", changes.Count);
+            activity?.SetTag("epss.change_count", changes.Count);
+
+            var totalSignals = 0;
+            var filteredCount = 0;
+
+            // Get all active tenants (S6)
+            var activeTenants = await _observedCveRepository.GetActiveTenantsAsync(cancellationToken);
+
+            if (activeTenants.Count == 0)
+            {
+                _logger.LogDebug("No active tenants found; using default tenant");
+                activeTenants = new[] { Guid.Empty };
+            }
+
+            // For each tenant, filter changes to only observed CVEs
+            foreach (var tenantId in activeTenants)
+            {
+                // Get CVE IDs from changes
+                var changeCveIds = changes.Select(c => c.CveId).Distinct().ToList();
+
+                // Filter to only observed CVEs for this tenant (S6)
+                var observedCves = await _observedCveRepository.FilterObservedAsync(
+                    tenantId,
+                    changeCveIds,
+                    cancellationToken);
+
+                var tenantChanges = changes
+                    .Where(c => observedCves.Contains(c.CveId))
+                    .ToArray();
+
+                if (tenantChanges.Length == 0)
+                {
+                    continue;
+                }
+
+                filteredCount += changes.Length - tenantChanges.Length;
+
+                foreach (var batch in tenantChanges.Chunk(opts.BatchSize))
+                {
+                    var signals = GenerateSignalsForBatch(
+                        batch,
+                        tenantId,
+                        modelDate.Value,
+                        currentModelVersion,
+                        isModelChange);
+
+                    if (signals.Count > 0)
+                    {
+                        // Store signals in database
+                        var created = await _signalRepository.CreateBulkAsync(signals, cancellationToken);
+                        totalSignals += created;
+
+                        // Publish signals to notification system (S9)
+                        var published = await _signalPublisher.PublishBatchAsync(signals, cancellationToken);
+                        _logger.LogDebug(
+                            "Published {Published}/{Total} EPSS signals for tenant {TenantId}",
+                            published,
+                            signals.Count,
+                            tenantId);
+                    }
+                }
+
+                // If model changed, emit summary signal per tenant (S8)
+                if (isModelChange)
+                {
+                    await EmitModelUpdatedSignalAsync(
+                        tenantId,
+                        modelDate.Value,
+                        _lastModelVersion!,
+                        currentModelVersion!,
+                        tenantChanges.Length,
+                        cancellationToken);
+                    totalSignals++;
+                }
+            }
+
+            stopwatch.Stop();
+
+            _logger.LogInformation(
+                "EPSS signal generation completed: signals={SignalCount}, changes={ChangeCount}, filtered={FilteredCount}, tenants={TenantCount}, duration={Duration}ms",
+                totalSignals,
+                changes.Count,
+                filteredCount,
+                activeTenants.Count,
+                stopwatch.ElapsedMilliseconds);
+
+            activity?.SetTag("epss.signal_count", totalSignals);
+            activity?.SetTag("epss.filtered_count", filteredCount);
+            activity?.SetTag("epss.tenant_count", activeTenants.Count);
+            activity?.SetTag("epss.duration_ms", stopwatch.ElapsedMilliseconds);
+        }
+        catch (Exception ex)
+        {
+            _logger.LogError(ex, "EPSS signal generation failed");
+            activity?.SetStatus(ActivityStatusCode.Error, ex.Message);
+            throw;
+        }
+    }
+
+    private IReadOnlyList<EpssSignal> GenerateSignalsForBatch(
+        EpssChangeRecord[] changes,
+        Guid tenantId,
+        DateOnly modelDate,
+        string? modelVersion,
+        bool isModelChange)
+    {
+        var signals = new List<EpssSignal>();
+
+        foreach (var change in changes)
+        {
+            // Skip generating individual signals on model change day if suppression is enabled
+            // (would check tenant config in production)
+            if (isModelChange && ShouldSuppressOnModelChange(change))
+            {
+                continue;
+            }
+
+            var eventType = DetermineEventType(change);
+            if (string.IsNullOrEmpty(eventType))
+            {
+                continue;
+            }
+
+            var dedupeKey = EpssExplainHashCalculator.ComputeDedupeKey(
+                modelDate,
+                change.CveId,
+                eventType,
+                change.PreviousBand.ToString(),
+                ComputeNewBand(change).ToString());
+
+            var explainHash = EpssExplainHashCalculator.ComputeExplainHash(
+                modelDate,
+                change.CveId,
+                eventType,
+                change.PreviousBand.ToString(),
+                ComputeNewBand(change).ToString(),
+                change.NewScore,
+                0, // Percentile would come from EPSS data
+                modelVersion);
+
+            var payload = JsonSerializer.Serialize(new
+            {
+                cveId = change.CveId,
+                oldScore = change.PreviousScore,
+                newScore = change.NewScore,
+                oldBand = change.PreviousBand.ToString(),
+                newBand = ComputeNewBand(change).ToString(),
+                flags = change.Flags.ToString(),
+                modelVersion
+            });
+
+            signals.Add(new EpssSignal
+            {
+                TenantId = tenantId,
+                ModelDate = modelDate,
+                CveId = change.CveId,
+                EventType = eventType,
+                RiskBand = ComputeNewBand(change).ToString(),
+                EpssScore = change.NewScore,
+                EpssDelta = change.NewScore - (change.PreviousScore ?? 0),
+                IsModelChange = isModelChange,
+                ModelVersion = modelVersion,
+                DedupeKey = dedupeKey,
+                ExplainHash = explainHash,
+                Payload = payload
+            });
+        }
+
+        return signals;
+    }
+
+    private static string? DetermineEventType(EpssChangeRecord change)
+    {
+        if (change.Flags.HasFlag(EpssChangeFlags.NewScored))
+        {
+            return EpssSignalEventTypes.NewHigh;
+        }
+
+        if (change.Flags.HasFlag(EpssChangeFlags.CrossedHigh))
+        {
+            return EpssSignalEventTypes.BandChange;
+        }
+
+        if (change.Flags.HasFlag(EpssChangeFlags.BigJumpUp))
+        {
+            return EpssSignalEventTypes.RiskSpike;
+        }
+
+        if (change.Flags.HasFlag(EpssChangeFlags.DroppedLow))
+        {
+            return EpssSignalEventTypes.DroppedLow;
+        }
+
+        return null;
+    }
+
+    private static EpssPriorityBand ComputeNewBand(EpssChangeRecord change)
+    {
+        // Simplified band calculation - would use EpssPriorityCalculator in production
+        if (change.NewScore >= 0.5)
+        {
+            return EpssPriorityBand.Critical;
+        }
+
+        if (change.NewScore >= 0.2)
+        {
+            return EpssPriorityBand.High;
+        }
+
+        if (change.NewScore >= 0.05)
+        {
+            return EpssPriorityBand.Medium;
+        }
+
+        return EpssPriorityBand.Low;
+    }
+
+    private static bool ShouldSuppressOnModelChange(EpssChangeRecord change)
+    {
+        // Suppress RISK_SPIKE and BAND_CHANGE on model change days to avoid alert storms
+        return change.Flags.HasFlag(EpssChangeFlags.BigJumpUp) ||
+               change.Flags.HasFlag(EpssChangeFlags.BigJumpDown) ||
+               change.Flags.HasFlag(EpssChangeFlags.CrossedHigh);
+    }
+
+    private async Task<string?> GetCurrentModelVersionAsync(DateOnly modelDate, CancellationToken cancellationToken)
+    {
+        // Would query from epss_import_run or epss_raw table
+        // For now, return a placeholder based on date
+        return $"v{modelDate:yyyy.MM.dd}";
+    }
+
+    private async Task<IReadOnlyList<EpssChangeRecord>> GetEpssChangesAsync(
+        DateOnly modelDate,
+        CancellationToken cancellationToken)
+    {
+        // TODO: Implement repository method to get changes from epss_changes table
+        // For now, return empty list
+        return Array.Empty<EpssChangeRecord>();
+    }
+
+    private async Task EmitModelUpdatedSignalAsync(
+        Guid tenantId,
+        DateOnly modelDate,
+        string oldVersion,
+        string newVersion,
+        int affectedCveCount,
+        CancellationToken cancellationToken)
+    {
+        var payload = JsonSerializer.Serialize(new
+        {
+            oldVersion,
+            newVersion,
+            affectedCveCount,
+            suppressedSignals = true
+        });
+
+        var signal = new EpssSignal
+        {
+            TenantId = tenantId,
+            ModelDate = modelDate,
+            CveId = "MODEL_UPDATE",
+            EventType = EpssSignalEventTypes.ModelUpdated,
+            IsModelChange = true,
+            ModelVersion = newVersion,
+            DedupeKey = $"{modelDate:yyyy-MM-dd}:MODEL_UPDATE:{oldVersion}->{newVersion}",
+            ExplainHash = EpssExplainHashCalculator.ComputeExplainHash(
+                modelDate,
+                "MODEL_UPDATE",
+                EpssSignalEventTypes.ModelUpdated,
+                oldVersion,
+                newVersion,
+                0,
+                0,
+                newVersion),
+            Payload = payload
+        };
+
+        await _signalRepository.CreateAsync(signal, cancellationToken);
+
+        _logger.LogInformation(
+            "Emitted MODEL_UPDATED signal: {OldVersion} -> {NewVersion}, affected {Count} CVEs",
+            oldVersion,
+            newVersion,
+            affectedCveCount);
+    }
+}

src/Scanner/StellaOps.Scanner.Worker/Processing/NativeAnalyzerExecutor.cs

@@ -3,11 +3,13 @@
 // Sprint: SPRINT_3500_0014_0001_native_analyzer_integration
 // Task: NAI-001
 // Description: Executes native binary analysis during container scans.
+// Note: NUC-004 (unknown classification) deferred - requires project reference.
 // -----------------------------------------------------------------------------
 
 using System.Diagnostics;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Options;
+using StellaOps.Scanner.Core.Contracts;
 using StellaOps.Scanner.Emit.Native;
 using StellaOps.Scanner.Worker.Diagnostics;
 using StellaOps.Scanner.Worker.Options;
@@ -281,4 +283,7 @@ public sealed record NativeAnalysisResult
 
     /// <summary>Emitted component results.</summary>
     public IReadOnlyList<NativeComponentEmitResult> Components { get; init; } = Array.Empty<NativeComponentEmitResult>();
+
+    /// <summary>Layer component fragments for SBOM merging.</summary>
+    public IReadOnlyList<LayerComponentFragment> LayerFragments { get; init; } = Array.Empty<LayerComponentFragment>();
 }

src/Scanner/StellaOps.Scanner.Worker/Processing/ScanStageNames.cs

@@ -9,6 +9,7 @@ public static class ScanStageNames
     public const string PullLayers = "pull-layers";
     public const string BuildFilesystem = "build-filesystem";
     public const string ExecuteAnalyzers = "execute-analyzers";
+    public const string EpssEnrichment = "epss-enrichment";
     public const string ComposeArtifacts = "compose-artifacts";
     public const string EmitReports = "emit-reports";
     public const string Entropy = "entropy";
@@ -20,8 +21,10 @@ public static class ScanStageNames
         PullLayers,
         BuildFilesystem,
         ExecuteAnalyzers,
+        EpssEnrichment,
         ComposeArtifacts,
         Entropy,
         EmitReports,
     };
 }
+

src/Scanner/StellaOps.Scanner.Worker/Program.cs

@@ -133,6 +133,7 @@ builder.Services.AddSingleton<ILanguageAnalyzerPluginCatalog, LanguageAnalyzerPl
 builder.Services.AddSingleton<IScanAnalyzerDispatcher, CompositeScanAnalyzerDispatcher>();
 builder.Services.AddSingleton<IScanStageExecutor, RegistrySecretStageExecutor>();
 builder.Services.AddSingleton<IScanStageExecutor, AnalyzerStageExecutor>();
+builder.Services.AddSingleton<IScanStageExecutor, EpssEnrichmentStageExecutor>();
 builder.Services.AddSingleton<IScanStageExecutor, Reachability.ReachabilityBuildStageExecutor>();
 builder.Services.AddSingleton<IScanStageExecutor, Reachability.ReachabilityPublishStageExecutor>();
 builder.Services.AddSingleton<IScanStageExecutor, EntropyStageExecutor>();

src/Scanner/__Libraries/StellaOps.Scanner.Reachability/Attestation/AttestingRichGraphWriter.cs

@@ -0,0 +1,146 @@
+// -----------------------------------------------------------------------------
+// AttestingRichGraphWriter.cs
+// Sprint: SPRINT_3620_0001_0001_reachability_witness_dsse
+// Description: RichGraphWriter wrapper that produces DSSE attestation alongside graph.
+// -----------------------------------------------------------------------------
+
+using System;
+using System.IO;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Options;
+
+namespace StellaOps.Scanner.Reachability.Attestation;
+
+/// <summary>
+/// Result of writing a rich graph with attestation.
+/// </summary>
+/// <param name="GraphPath">Path to the richgraph-v1.json file.</param>
+/// <param name="MetaPath">Path to the meta.json file.</param>
+/// <param name="GraphHash">Content-addressed hash of the graph.</param>
+/// <param name="NodeCount">Number of nodes in the graph.</param>
+/// <param name="EdgeCount">Number of edges in the graph.</param>
+/// <param name="AttestationPath">Path to the attestation DSSE envelope (if produced).</param>
+/// <param name="WitnessResult">Detailed witness publication result (if attestation enabled).</param>
+public sealed record AttestingRichGraphWriteResult(
+    string GraphPath,
+    string MetaPath,
+    string GraphHash,
+    int NodeCount,
+    int EdgeCount,
+    string? AttestationPath,
+    ReachabilityWitnessPublishResult? WitnessResult);
+
+/// <summary>
+/// Writes richgraph-v1 documents with optional DSSE attestation.
+/// Wraps <see cref="RichGraphWriter"/> and integrates with <see cref="IReachabilityWitnessPublisher"/>.
+/// </summary>
+public sealed class AttestingRichGraphWriter
+{
+    private readonly RichGraphWriter _graphWriter;
+    private readonly IReachabilityWitnessPublisher _witnessPublisher;
+    private readonly ReachabilityWitnessOptions _options;
+    private readonly ILogger<AttestingRichGraphWriter> _logger;
+
+    /// <summary>
+    /// Creates a new attesting rich graph writer.
+    /// </summary>
+    public AttestingRichGraphWriter(
+        RichGraphWriter graphWriter,
+        IReachabilityWitnessPublisher witnessPublisher,
+        IOptions<ReachabilityWitnessOptions> options,
+        ILogger<AttestingRichGraphWriter> logger)
+    {
+        _graphWriter = graphWriter ?? throw new ArgumentNullException(nameof(graphWriter));
+        _witnessPublisher = witnessPublisher ?? throw new ArgumentNullException(nameof(witnessPublisher));
+        _options = options?.Value ?? throw new ArgumentNullException(nameof(options));
+        _logger = logger ?? throw new ArgumentNullException(nameof(logger));
+    }
+
+    /// <summary>
+    /// Writes the rich graph and produces attestation if enabled.
+    /// </summary>
+    /// <param name="graph">The rich graph to write.</param>
+    /// <param name="outputRoot">Root output directory.</param>
+    /// <param name="analysisId">Analysis identifier.</param>
+    /// <param name="subjectDigest">Subject artifact digest for attestation.</param>
+    /// <param name="policyHash">Optional policy hash for attestation.</param>
+    /// <param name="sourceCommit">Optional source commit for attestation.</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>Write result including attestation details.</returns>
+    public async Task<AttestingRichGraphWriteResult> WriteWithAttestationAsync(
+        RichGraph graph,
+        string outputRoot,
+        string analysisId,
+        string subjectDigest,
+        string? policyHash = null,
+        string? sourceCommit = null,
+        CancellationToken cancellationToken = default)
+    {
+        ArgumentNullException.ThrowIfNull(graph);
+        ArgumentException.ThrowIfNullOrWhiteSpace(outputRoot);
+        ArgumentException.ThrowIfNullOrWhiteSpace(analysisId);
+        ArgumentException.ThrowIfNullOrWhiteSpace(subjectDigest);
+
+        // Step 1: Write the graph using the standard writer
+        var writeResult = await _graphWriter.WriteAsync(graph, outputRoot, analysisId, cancellationToken)
+            .ConfigureAwait(false);
+
+        _logger.LogDebug(
+            "Wrote rich graph: {GraphPath}, hash={GraphHash}, nodes={NodeCount}, edges={EdgeCount}",
+            writeResult.GraphPath,
+            writeResult.GraphHash,
+            writeResult.NodeCount,
+            writeResult.EdgeCount);
+
+        // Step 2: Produce attestation if enabled
+        string? attestationPath = null;
+        ReachabilityWitnessPublishResult? witnessResult = null;
+
+        if (_options.Enabled)
+        {
+            // Read the graph bytes for attestation
+            var graphBytes = await File.ReadAllBytesAsync(writeResult.GraphPath, cancellationToken)
+                .ConfigureAwait(false);
+
+            // Publish witness attestation
+            witnessResult = await _witnessPublisher.PublishAsync(
+                graph,
+                graphBytes,
+                writeResult.GraphHash,
+                subjectDigest,
+                policyHash,
+                sourceCommit,
+                cancellationToken).ConfigureAwait(false);
+
+            // Write DSSE envelope to disk alongside the graph
+            if (witnessResult.DsseEnvelopeBytes.Length > 0)
+            {
+                var graphDir = Path.GetDirectoryName(writeResult.GraphPath)!;
+                attestationPath = Path.Combine(graphDir, "richgraph-v1.dsse.json");
+
+                await File.WriteAllBytesAsync(attestationPath, witnessResult.DsseEnvelopeBytes, cancellationToken)
+                    .ConfigureAwait(false);
+
+                _logger.LogInformation(
+                    "Wrote reachability witness attestation: {AttestationPath}, statementHash={StatementHash}",
+                    attestationPath,
+                    witnessResult.StatementHash);
+            }
+        }
+        else
+        {
+            _logger.LogDebug("Reachability witness attestation is disabled");
+        }
+
+        return new AttestingRichGraphWriteResult(
+            GraphPath: writeResult.GraphPath,
+            MetaPath: writeResult.MetaPath,
+            GraphHash: writeResult.GraphHash,
+            NodeCount: writeResult.NodeCount,
+            EdgeCount: writeResult.EdgeCount,
+            AttestationPath: attestationPath,
+            WitnessResult: witnessResult);
+    }
+}

src/Scanner/__Libraries/StellaOps.Scanner.Reachability/Attestation/ReachabilityAttestationServiceCollectionExtensions.cs

@@ -0,0 +1,52 @@
+// -----------------------------------------------------------------------------
+// ReachabilityAttestationServiceCollectionExtensions.cs
+// Sprint: SPRINT_3620_0001_0001_reachability_witness_dsse
+// Description: DI registration for reachability witness attestation services.
+// -----------------------------------------------------------------------------
+
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.DependencyInjection.Extensions;
+
+namespace StellaOps.Scanner.Reachability.Attestation;
+
+/// <summary>
+/// Extension methods for registering reachability witness attestation services.
+/// </summary>
+public static class ReachabilityAttestationServiceCollectionExtensions
+{
+    /// <summary>
+    /// Adds reachability witness attestation services to the service collection.
+    /// </summary>
+    /// <param name="services">The service collection.</param>
+    /// <returns>The service collection for chaining.</returns>
+    public static IServiceCollection AddReachabilityWitnessAttestation(this IServiceCollection services)
+    {
+        // Register DSSE builder
+        services.TryAddSingleton<ReachabilityWitnessDsseBuilder>();
+
+        // Register publisher
+        services.TryAddSingleton<IReachabilityWitnessPublisher, ReachabilityWitnessPublisher>();
+
+        // Register attesting writer (wraps RichGraphWriter)
+        services.TryAddSingleton<AttestingRichGraphWriter>();
+
+        // Register options
+        services.AddOptions<ReachabilityWitnessOptions>();
+
+        return services;
+    }
+
+    /// <summary>
+    /// Configures reachability witness options.
+    /// </summary>
+    /// <param name="services">The service collection.</param>
+    /// <param name="configure">Configuration action.</param>
+    /// <returns>The service collection for chaining.</returns>
+    public static IServiceCollection ConfigureReachabilityWitnessOptions(
+        this IServiceCollection services,
+        Action<ReachabilityWitnessOptions> configure)
+    {
+        services.Configure(configure);
+        return services;
+    }
+}

src/Scanner/__Libraries/StellaOps.Scanner.Storage/Epss/CachingEpssProvider.cs

@@ -0,0 +1,338 @@
+// -----------------------------------------------------------------------------
+// CachingEpssProvider.cs
+// Sprint: SPRINT_3410_0002_0001_epss_scanner_integration
+// Task: EPSS-SCAN-005
+// Description: Valkey/Redis cache layer for EPSS lookups.
+// -----------------------------------------------------------------------------
+
+using System.Diagnostics;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Options;
+using StellaOps.Messaging.Abstractions;
+using StellaOps.Scanner.Core.Epss;
+
+namespace StellaOps.Scanner.Storage.Epss;
+
+/// <summary>
+/// Caching decorator for <see cref="IEpssProvider"/> that uses Valkey/Redis.
+/// Provides read-through caching for EPSS score lookups.
+/// </summary>
+public sealed class CachingEpssProvider : IEpssProvider
+{
+    private const string CacheKeyPrefix = "epss:current:";
+    private const string ModelDateCacheKey = "epss:model-date";
+
+    private readonly IEpssProvider _innerProvider;
+    private readonly IDistributedCache<EpssCacheEntry>? _cache;
+    private readonly EpssProviderOptions _options;
+    private readonly ILogger<CachingEpssProvider> _logger;
+    private readonly TimeProvider _timeProvider;
+
+    public CachingEpssProvider(
+        IEpssProvider innerProvider,
+        IDistributedCache<EpssCacheEntry>? cache,
+        IOptions<EpssProviderOptions> options,
+        ILogger<CachingEpssProvider> logger,
+        TimeProvider? timeProvider = null)
+    {
+        _innerProvider = innerProvider ?? throw new ArgumentNullException(nameof(innerProvider));
+        _cache = cache; // Can be null if caching is disabled
+        _options = options?.Value ?? throw new ArgumentNullException(nameof(options));
+        _logger = logger ?? throw new ArgumentNullException(nameof(logger));
+        _timeProvider = timeProvider ?? TimeProvider.System;
+    }
+
+    public async Task<EpssEvidence?> GetCurrentAsync(string cveId, CancellationToken cancellationToken = default)
+    {
+        ArgumentException.ThrowIfNullOrWhiteSpace(cveId);
+
+        // If caching is disabled or cache is unavailable, go directly to inner provider
+        if (!_options.EnableCache || _cache is null)
+        {
+            return await _innerProvider.GetCurrentAsync(cveId, cancellationToken).ConfigureAwait(false);
+        }
+
+        var cacheKey = BuildCacheKey(cveId);
+
+        try
+        {
+            var cacheResult = await _cache.GetAsync(cacheKey, cancellationToken).ConfigureAwait(false);
+
+            if (cacheResult.IsHit && cacheResult.Value is not null)
+            {
+                _logger.LogDebug("Cache hit for EPSS score: {CveId}", cveId);
+                return MapFromCacheEntry(cacheResult.Value, fromCache: true);
+            }
+        }
+        catch (Exception ex)
+        {
+            // Cache failures should not block the request
+            _logger.LogWarning(ex, "Cache lookup failed for {CveId}, falling back to database", cveId);
+        }
+
+        // Cache miss - fetch from database
+        var evidence = await _innerProvider.GetCurrentAsync(cveId, cancellationToken).ConfigureAwait(false);
+
+        if (evidence is not null)
+        {
+            await TryCacheAsync(cacheKey, evidence, cancellationToken).ConfigureAwait(false);
+        }
+
+        return evidence;
+    }
+
+    public async Task<EpssBatchResult> GetCurrentBatchAsync(
+        IEnumerable<string> cveIds,
+        CancellationToken cancellationToken = default)
+    {
+        ArgumentNullException.ThrowIfNull(cveIds);
+
+        var cveIdList = cveIds.Distinct(StringComparer.OrdinalIgnoreCase).ToList();
+        if (cveIdList.Count == 0)
+        {
+            return new EpssBatchResult
+            {
+                Found = Array.Empty<EpssEvidence>(),
+                NotFound = Array.Empty<string>(),
+                ModelDate = DateOnly.FromDateTime(_timeProvider.GetUtcNow().Date),
+                LookupTimeMs = 0
+            };
+        }
+
+        // If caching is disabled, go directly to inner provider
+        if (!_options.EnableCache || _cache is null)
+        {
+            return await _innerProvider.GetCurrentBatchAsync(cveIdList, cancellationToken).ConfigureAwait(false);
+        }
+
+        var sw = Stopwatch.StartNew();
+        var found = new List<EpssEvidence>();
+        var notInCache = new List<string>();
+        var cacheHits = 0;
+        DateOnly? modelDate = null;
+
+        // Try cache first for each CVE
+        foreach (var cveId in cveIdList)
+        {
+            try
+            {
+                var cacheKey = BuildCacheKey(cveId);
+                var cacheResult = await _cache.GetAsync(cacheKey, cancellationToken).ConfigureAwait(false);
+
+                if (cacheResult.IsHit && cacheResult.Value is not null)
+                {
+                    var evidence = MapFromCacheEntry(cacheResult.Value, fromCache: true);
+                    found.Add(evidence);
+                    modelDate ??= evidence.ModelDate;
+                    cacheHits++;
+                }
+                else
+                {
+                    notInCache.Add(cveId);
+                }
+            }
+            catch (Exception ex)
+            {
+                // Cache failure - will need to fetch from DB
+                _logger.LogDebug(ex, "Cache lookup failed for {CveId}", cveId);
+                notInCache.Add(cveId);
+            }
+        }
+
+        _logger.LogDebug(
+            "EPSS cache: {CacheHits}/{Total} hits, {CacheMisses} to fetch from database",
+            cacheHits,
+            cveIdList.Count,
+            notInCache.Count);
+
+        // Fetch remaining from database
+        if (notInCache.Count > 0)
+        {
+            var dbResult = await _innerProvider.GetCurrentBatchAsync(notInCache, cancellationToken).ConfigureAwait(false);
+
+            foreach (var evidence in dbResult.Found)
+            {
+                found.Add(evidence);
+                modelDate ??= evidence.ModelDate;
+
+                // Populate cache
+                await TryCacheAsync(BuildCacheKey(evidence.CveId), evidence, cancellationToken).ConfigureAwait(false);
+            }
+
+            // Add CVEs not found in database to the not found list
+            var notFound = dbResult.NotFound.ToList();
+
+            sw.Stop();
+
+            return new EpssBatchResult
+            {
+                Found = found,
+                NotFound = notFound,
+                ModelDate = modelDate ?? DateOnly.FromDateTime(_timeProvider.GetUtcNow().Date),
+                LookupTimeMs = sw.ElapsedMilliseconds,
+                PartiallyFromCache = cacheHits > 0 && notInCache.Count > 0
+            };
+        }
+
+        sw.Stop();
+
+        return new EpssBatchResult
+        {
+            Found = found,
+            NotFound = Array.Empty<string>(),
+            ModelDate = modelDate ?? DateOnly.FromDateTime(_timeProvider.GetUtcNow().Date),
+            LookupTimeMs = sw.ElapsedMilliseconds,
+            PartiallyFromCache = cacheHits > 0
+        };
+    }
+
+    public Task<EpssEvidence?> GetAsOfDateAsync(
+        string cveId,
+        DateOnly asOfDate,
+        CancellationToken cancellationToken = default)
+    {
+        // Historical lookups are not cached - they're typically one-off queries
+        return _innerProvider.GetAsOfDateAsync(cveId, asOfDate, cancellationToken);
+    }
+
+    public Task<IReadOnlyList<EpssEvidence>> GetHistoryAsync(
+        string cveId,
+        DateOnly startDate,
+        DateOnly endDate,
+        CancellationToken cancellationToken = default)
+    {
+        // History lookups are not cached
+        return _innerProvider.GetHistoryAsync(cveId, startDate, endDate, cancellationToken);
+    }
+
+    public async Task<DateOnly?> GetLatestModelDateAsync(CancellationToken cancellationToken = default)
+    {
+        // Try cache first (short TTL for model date)
+        if (_options.EnableCache && _cache is not null)
+        {
+            try
+            {
+                var cacheResult = await _cache.GetAsync(ModelDateCacheKey, cancellationToken).ConfigureAwait(false);
+
+                if (cacheResult.IsHit && cacheResult.Value?.ModelDate is not null)
+                {
+                    return cacheResult.Value.ModelDate;
+                }
+            }
+            catch (Exception ex)
+            {
+                _logger.LogDebug(ex, "Cache lookup failed for model date");
+            }
+        }
+
+        var modelDate = await _innerProvider.GetLatestModelDateAsync(cancellationToken).ConfigureAwait(false);
+
+        // Cache model date with shorter TTL (5 minutes)
+        if (modelDate.HasValue && _options.EnableCache && _cache is not null)
+        {
+            try
+            {
+                await _cache.SetAsync(
+                    ModelDateCacheKey,
+                    new EpssCacheEntry { ModelDate = modelDate.Value },
+                    new CacheEntryOptions { TimeToLive = TimeSpan.FromMinutes(5) },
+                    cancellationToken).ConfigureAwait(false);
+            }
+            catch (Exception ex)
+            {
+                _logger.LogDebug(ex, "Failed to cache model date");
+            }
+        }
+
+        return modelDate;
+    }
+
+    public Task<bool> IsAvailableAsync(CancellationToken cancellationToken = default)
+    {
+        return _innerProvider.IsAvailableAsync(cancellationToken);
+    }
+
+    /// <summary>
+    /// Invalidates all cached EPSS scores. Called after new EPSS data is ingested.
+    /// </summary>
+    public async Task InvalidateCacheAsync(CancellationToken cancellationToken = default)
+    {
+        if (_cache is null)
+        {
+            return;
+        }
+
+        try
+        {
+            var invalidated = await _cache.InvalidateByPatternAsync($"{CacheKeyPrefix}*", cancellationToken).ConfigureAwait(false);
+            await _cache.InvalidateAsync(ModelDateCacheKey, cancellationToken).ConfigureAwait(false);
+
+            _logger.LogInformation("Invalidated {Count} EPSS cache entries", invalidated + 1);
+        }
+        catch (Exception ex)
+        {
+            _logger.LogWarning(ex, "Failed to invalidate EPSS cache");
+        }
+    }
+
+    private static string BuildCacheKey(string cveId)
+    {
+        return $"{CacheKeyPrefix}{cveId.ToUpperInvariant()}";
+    }
+
+    private async Task TryCacheAsync(string cacheKey, EpssEvidence evidence, CancellationToken cancellationToken)
+    {
+        if (_cache is null)
+        {
+            return;
+        }
+
+        try
+        {
+            var cacheEntry = new EpssCacheEntry
+            {
+                CveId = evidence.CveId,
+                Score = evidence.Score,
+                Percentile = evidence.Percentile,
+                ModelDate = evidence.ModelDate,
+                CachedAt = _timeProvider.GetUtcNow()
+            };
+
+            await _cache.SetAsync(
+                cacheKey,
+                cacheEntry,
+                new CacheEntryOptions { TimeToLive = _options.CacheTtl },
+                cancellationToken).ConfigureAwait(false);
+        }
+        catch (Exception ex)
+        {
+            _logger.LogDebug(ex, "Failed to cache EPSS score for {CveId}", evidence.CveId);
+        }
+    }
+
+    private EpssEvidence MapFromCacheEntry(EpssCacheEntry entry, bool fromCache)
+    {
+        return new EpssEvidence
+        {
+            CveId = entry.CveId ?? string.Empty,
+            Score = entry.Score,
+            Percentile = entry.Percentile,
+            ModelDate = entry.ModelDate,
+            CapturedAt = entry.CachedAt,
+            Source = "cache",
+            FromCache = fromCache
+        };
+    }
+}
+
+/// <summary>
+/// Cache entry for EPSS scores.
+/// </summary>
+public sealed class EpssCacheEntry
+{
+    public string? CveId { get; set; }
+    public double Score { get; set; }
+    public double Percentile { get; set; }
+    public DateOnly ModelDate { get; set; }
+    public DateTimeOffset CachedAt { get; set; }
+}

src/Scanner/__Libraries/StellaOps.Scanner.Storage/Epss/EpssChangeRecord.cs

@@ -0,0 +1,51 @@
+// -----------------------------------------------------------------------------
+// EpssChangeRecord.cs
+// Sprint: SPRINT_3413_0001_0001_epss_live_enrichment
+// Task: #3 - Implement epss_changes flag logic
+// Description: Record representing an EPSS change that needs processing.
+// -----------------------------------------------------------------------------
+
+using StellaOps.Scanner.Core.Epss;
+
+namespace StellaOps.Scanner.Storage.Epss;
+
+/// <summary>
+/// Record representing an EPSS change that needs processing.
+/// </summary>
+public sealed record EpssChangeRecord
+{
+    /// <summary>
+    /// CVE identifier.
+    /// </summary>
+    public required string CveId { get; init; }
+
+    /// <summary>
+    /// Change flags indicating what changed.
+    /// </summary>
+    public EpssChangeFlags Flags { get; init; }
+
+    /// <summary>
+    /// Previous EPSS score (if available).
+    /// </summary>
+    public double? PreviousScore { get; init; }
+
+    /// <summary>
+    /// New EPSS score.
+    /// </summary>
+    public double NewScore { get; init; }
+
+    /// <summary>
+    /// New EPSS percentile.
+    /// </summary>
+    public double NewPercentile { get; init; }
+
+    /// <summary>
+    /// Previous priority band (if available).
+    /// </summary>
+    public EpssPriorityBand PreviousBand { get; init; }
+
+    /// <summary>
+    /// Model date for this change.
+    /// </summary>
+    public DateOnly ModelDate { get; init; }
+}

src/Scanner/__Libraries/StellaOps.Scanner.Storage/Epss/EpssExplainHashCalculator.cs

@@ -0,0 +1,110 @@
+// -----------------------------------------------------------------------------
+// EpssExplainHashCalculator.cs
+// Sprint: SPRINT_3413_0001_0001_epss_live_enrichment
+// Task: S4 - Implement ComputeExplainHash
+// Description: Deterministic SHA-256 hash calculator for EPSS signal explainability.
+// -----------------------------------------------------------------------------
+
+using System.Security.Cryptography;
+using System.Text;
+using System.Text.Json;
+
+namespace StellaOps.Scanner.Storage.Epss;
+
+/// <summary>
+/// Calculator for deterministic explain hashes on EPSS signals.
+/// The explain hash provides a unique fingerprint for signal inputs,
+/// enabling audit trails and change detection.
+/// </summary>
+public static class EpssExplainHashCalculator
+{
+    private static readonly JsonSerializerOptions JsonOptions = new()
+    {
+        PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
+        WriteIndented = false
+    };
+
+    /// <summary>
+    /// Computes a deterministic SHA-256 hash from signal input parameters.
+    /// </summary>
+    /// <param name="modelDate">EPSS model date.</param>
+    /// <param name="cveId">CVE identifier.</param>
+    /// <param name="eventType">Event type (RISK_SPIKE, BAND_CHANGE, etc.).</param>
+    /// <param name="oldBand">Previous risk band (nullable).</param>
+    /// <param name="newBand">New risk band (nullable).</param>
+    /// <param name="score">EPSS score.</param>
+    /// <param name="percentile">EPSS percentile.</param>
+    /// <param name="modelVersion">EPSS model version.</param>
+    /// <returns>SHA-256 hash as byte array.</returns>
+    public static byte[] ComputeExplainHash(
+        DateOnly modelDate,
+        string cveId,
+        string eventType,
+        string? oldBand,
+        string? newBand,
+        double score,
+        double percentile,
+        string? modelVersion)
+    {
+        // Create deterministic input structure
+        var input = new ExplainHashInput
+        {
+            ModelDate = modelDate.ToString("yyyy-MM-dd"),
+            CveId = cveId.ToUpperInvariant(), // Normalize CVE ID
+            EventType = eventType.ToUpperInvariant(),
+            OldBand = oldBand?.ToUpperInvariant() ?? "NONE",
+            NewBand = newBand?.ToUpperInvariant() ?? "NONE",
+            Score = Math.Round(score, 6), // Consistent precision
+            Percentile = Math.Round(percentile, 6),
+            ModelVersion = modelVersion ?? string.Empty
+        };
+
+        // Serialize to deterministic JSON
+        var json = JsonSerializer.Serialize(input, JsonOptions);
+        var bytes = Encoding.UTF8.GetBytes(json);
+
+        return SHA256.HashData(bytes);
+    }
+
+    /// <summary>
+    /// Computes the dedupe key for an EPSS signal.
+    /// This key is used to prevent duplicate signals.
+    /// </summary>
+    /// <param name="modelDate">EPSS model date.</param>
+    /// <param name="cveId">CVE identifier.</param>
+    /// <param name="eventType">Event type.</param>
+    /// <param name="oldBand">Previous risk band.</param>
+    /// <param name="newBand">New risk band.</param>
+    /// <returns>Deterministic dedupe key string.</returns>
+    public static string ComputeDedupeKey(
+        DateOnly modelDate,
+        string cveId,
+        string eventType,
+        string? oldBand,
+        string? newBand)
+    {
+        return $"{modelDate:yyyy-MM-dd}:{cveId.ToUpperInvariant()}:{eventType.ToUpperInvariant()}:{oldBand?.ToUpperInvariant() ?? "NONE"}->{newBand?.ToUpperInvariant() ?? "NONE"}";
+    }
+
+    /// <summary>
+    /// Converts an explain hash to hex string for display.
+    /// </summary>
+    /// <param name="hash">The hash bytes.</param>
+    /// <returns>Lowercase hex string.</returns>
+    public static string ToHexString(byte[] hash)
+    {
+        return Convert.ToHexString(hash).ToLowerInvariant();
+    }
+
+    private sealed record ExplainHashInput
+    {
+        public required string ModelDate { get; init; }
+        public required string CveId { get; init; }
+        public required string EventType { get; init; }
+        public required string OldBand { get; init; }
+        public required string NewBand { get; init; }
+        public required double Score { get; init; }
+        public required double Percentile { get; init; }
+        public required string ModelVersion { get; init; }
+    }
+}

src/Scanner/__Libraries/StellaOps.Scanner.Storage/Epss/EpssReplayService.cs

@@ -0,0 +1,285 @@
+// -----------------------------------------------------------------------------
+// EpssReplayService.cs
+// Sprint: SPRINT_3413_0001_0001_epss_live_enrichment
+// Task: R4 - Implement ReplayFromRawAsync
+// Description: Service for replaying EPSS data from stored raw payloads.
+// -----------------------------------------------------------------------------
+
+using System.Runtime.CompilerServices;
+using System.Text.Json;
+using Microsoft.Extensions.Logging;
+using StellaOps.Scanner.Storage.Repositories;
+
+namespace StellaOps.Scanner.Storage.Epss;
+
+/// <summary>
+/// Result of an EPSS replay operation.
+/// </summary>
+public sealed record EpssReplayResult
+{
+    /// <summary>
+    /// The model date that was replayed.
+    /// </summary>
+    public required DateOnly ModelDate { get; init; }
+
+    /// <summary>
+    /// Number of rows replayed.
+    /// </summary>
+    public required int RowCount { get; init; }
+
+    /// <summary>
+    /// Number of distinct CVEs.
+    /// </summary>
+    public required int DistinctCveCount { get; init; }
+
+    /// <summary>
+    /// Whether this was a dry run (no writes).
+    /// </summary>
+    public required bool IsDryRun { get; init; }
+
+    /// <summary>
+    /// Duration of the replay in milliseconds.
+    /// </summary>
+    public required long DurationMs { get; init; }
+
+    /// <summary>
+    /// Model version from the raw payload.
+    /// </summary>
+    public string? ModelVersion { get; init; }
+}
+
+/// <summary>
+/// Service for replaying EPSS data from stored raw payloads.
+/// Enables deterministic re-normalization without re-downloading from FIRST.org.
+/// </summary>
+public sealed class EpssReplayService
+{
+    private readonly IEpssRawRepository _rawRepository;
+    private readonly IEpssRepository _epssRepository;
+    private readonly TimeProvider _timeProvider;
+    private readonly ILogger<EpssReplayService> _logger;
+
+    public EpssReplayService(
+        IEpssRawRepository rawRepository,
+        IEpssRepository epssRepository,
+        TimeProvider timeProvider,
+        ILogger<EpssReplayService> logger)
+    {
+        _rawRepository = rawRepository ?? throw new ArgumentNullException(nameof(rawRepository));
+        _epssRepository = epssRepository ?? throw new ArgumentNullException(nameof(epssRepository));
+        _timeProvider = timeProvider ?? throw new ArgumentNullException(nameof(timeProvider));
+        _logger = logger ?? throw new ArgumentNullException(nameof(logger));
+    }
+
+    /// <summary>
+    /// Replays EPSS data from a stored raw payload for a specific date.
+    /// Re-normalizes the data into the epss_snapshot table without re-downloading.
+    /// </summary>
+    /// <param name="modelDate">The model date to replay.</param>
+    /// <param name="dryRun">If true, validates but doesn't write.</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>Result of the replay operation.</returns>
+    public async Task<EpssReplayResult> ReplayFromRawAsync(
+        DateOnly modelDate,
+        bool dryRun = false,
+        CancellationToken cancellationToken = default)
+    {
+        var stopwatch = System.Diagnostics.Stopwatch.StartNew();
+
+        _logger.LogInformation(
+            "Starting EPSS replay from raw for {ModelDate} (dryRun={DryRun})",
+            modelDate,
+            dryRun);
+
+        // Fetch the raw payload
+        var raw = await _rawRepository.GetByDateAsync(modelDate, cancellationToken).ConfigureAwait(false);
+
+        if (raw is null)
+        {
+            throw new InvalidOperationException($"No raw EPSS payload found for {modelDate}");
+        }
+
+        _logger.LogDebug(
+            "Found raw payload: rawId={RawId}, rows={RowCount}, modelVersion={ModelVersion}",
+            raw.RawId,
+            raw.RowCount,
+            raw.ModelVersion);
+
+        // Parse the JSON payload
+        var rows = ParseRawPayload(raw.Payload);
+
+        if (dryRun)
+        {
+            stopwatch.Stop();
+
+            _logger.LogInformation(
+                "EPSS replay dry run completed: modelDate={ModelDate}, rows={RowCount}, cves={CveCount}, duration={Duration}ms",
+                modelDate,
+                rows.Count,
+                rows.Select(r => r.CveId).Distinct().Count(),
+                stopwatch.ElapsedMilliseconds);
+
+            return new EpssReplayResult
+            {
+                ModelDate = modelDate,
+                RowCount = rows.Count,
+                DistinctCveCount = rows.Select(r => r.CveId).Distinct().Count(),
+                IsDryRun = true,
+                DurationMs = stopwatch.ElapsedMilliseconds,
+                ModelVersion = raw.ModelVersion
+            };
+        }
+
+        // Create a new import run for the replay
+        var importRun = await _epssRepository.BeginImportAsync(
+            modelDate,
+            $"replay:{raw.SourceUri}",
+            _timeProvider.GetUtcNow(),
+            Convert.ToHexString(raw.PayloadSha256).ToLowerInvariant(),
+            cancellationToken).ConfigureAwait(false);
+
+        try
+        {
+            // Write the snapshot using async enumerable
+            var writeResult = await _epssRepository.WriteSnapshotAsync(
+                importRun.ImportRunId,
+                modelDate,
+                _timeProvider.GetUtcNow(),
+                ToAsyncEnumerable(rows),
+                cancellationToken).ConfigureAwait(false);
+
+            // Mark success
+            await _epssRepository.MarkImportSucceededAsync(
+                importRun.ImportRunId,
+                rows.Count,
+                Convert.ToHexString(raw.PayloadSha256).ToLowerInvariant(),
+                raw.ModelVersion,
+                raw.PublishedDate,
+                cancellationToken).ConfigureAwait(false);
+
+            stopwatch.Stop();
+
+            _logger.LogInformation(
+                "EPSS replay completed: modelDate={ModelDate}, rows={RowCount}, cves={CveCount}, duration={Duration}ms",
+                modelDate,
+                writeResult.RowCount,
+                writeResult.DistinctCveCount,
+                stopwatch.ElapsedMilliseconds);
+
+            return new EpssReplayResult
+            {
+                ModelDate = modelDate,
+                RowCount = writeResult.RowCount,
+                DistinctCveCount = writeResult.DistinctCveCount,
+                IsDryRun = false,
+                DurationMs = stopwatch.ElapsedMilliseconds,
+                ModelVersion = raw.ModelVersion
+            };
+        }
+        catch (Exception ex)
+        {
+            await _epssRepository.MarkImportFailedAsync(
+                importRun.ImportRunId,
+                $"Replay failed: {ex.Message}",
+                cancellationToken).ConfigureAwait(false);
+
+            throw;
+        }
+    }
+
+    /// <summary>
+    /// Replays EPSS data for a date range.
+    /// </summary>
+    /// <param name="startDate">Start date (inclusive).</param>
+    /// <param name="endDate">End date (inclusive).</param>
+    /// <param name="dryRun">If true, validates but doesn't write.</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>Results for each date replayed.</returns>
+    public async Task<IReadOnlyList<EpssReplayResult>> ReplayRangeAsync(
+        DateOnly startDate,
+        DateOnly endDate,
+        bool dryRun = false,
+        CancellationToken cancellationToken = default)
+    {
+        var results = new List<EpssReplayResult>();
+
+        var rawPayloads = await _rawRepository.GetByDateRangeAsync(startDate, endDate, cancellationToken)
+            .ConfigureAwait(false);
+
+        _logger.LogInformation(
+            "Replaying {Count} EPSS payloads from {StartDate} to {EndDate}",
+            rawPayloads.Count,
+            startDate,
+            endDate);
+
+        foreach (var raw in rawPayloads.OrderBy(r => r.AsOfDate))
+        {
+            try
+            {
+                var result = await ReplayFromRawAsync(raw.AsOfDate, dryRun, cancellationToken)
+                    .ConfigureAwait(false);
+                results.Add(result);
+            }
+            catch (Exception ex)
+            {
+                _logger.LogError(ex, "Failed to replay EPSS for {ModelDate}", raw.AsOfDate);
+                // Continue with next date
+            }
+        }
+
+        return results;
+    }
+
+    /// <summary>
+    /// Gets available dates for replay.
+    /// </summary>
+    /// <param name="startDate">Optional start date filter.</param>
+    /// <param name="endDate">Optional end date filter.</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>List of available model dates.</returns>
+    public async Task<IReadOnlyList<DateOnly>> GetAvailableDatesAsync(
+        DateOnly? startDate = null,
+        DateOnly? endDate = null,
+        CancellationToken cancellationToken = default)
+    {
+        var start = startDate ?? DateOnly.FromDateTime(DateTime.UtcNow.AddYears(-1));
+        var end = endDate ?? DateOnly.FromDateTime(DateTime.UtcNow);
+
+        var rawPayloads = await _rawRepository.GetByDateRangeAsync(start, end, cancellationToken)
+            .ConfigureAwait(false);
+
+        return rawPayloads.Select(r => r.AsOfDate).OrderByDescending(d => d).ToList();
+    }
+
+    private static List<EpssScoreRow> ParseRawPayload(string jsonPayload)
+    {
+        var rows = new List<EpssScoreRow>();
+
+        using var doc = JsonDocument.Parse(jsonPayload);
+
+        foreach (var element in doc.RootElement.EnumerateArray())
+        {
+            var cveId = element.GetProperty("cve").GetString();
+            var score = element.GetProperty("epss").GetDouble();
+            var percentile = element.GetProperty("percentile").GetDouble();
+
+            if (!string.IsNullOrEmpty(cveId))
+            {
+                rows.Add(new EpssScoreRow(cveId, score, percentile));
+            }
+        }
+
+        return rows;
+    }
+
+    private static async IAsyncEnumerable<EpssScoreRow> ToAsyncEnumerable(
+        IEnumerable<EpssScoreRow> rows)
+    {
+        foreach (var row in rows)
+        {
+            yield return row;
+        }
+
+        await Task.CompletedTask;
+    }
+}

src/Scanner/__Libraries/StellaOps.Scanner.Storage/Epss/IEpssSignalPublisher.cs

@@ -0,0 +1,104 @@
+// -----------------------------------------------------------------------------
+// IEpssSignalPublisher.cs
+// Sprint: SPRINT_3413_0001_0001_epss_live_enrichment
+// Task: S9 - Connect to Notify/Router
+// Description: Interface for publishing EPSS signals to the notification system.
+// -----------------------------------------------------------------------------
+
+using StellaOps.Scanner.Storage.Repositories;
+
+namespace StellaOps.Scanner.Storage.Epss;
+
+/// <summary>
+/// Result of publishing an EPSS signal.
+/// </summary>
+public sealed record EpssSignalPublishResult
+{
+    /// <summary>
+    /// Whether the publish was successful.
+    /// </summary>
+    public required bool Success { get; init; }
+
+    /// <summary>
+    /// Message ID from the queue (if applicable).
+    /// </summary>
+    public string? MessageId { get; init; }
+
+    /// <summary>
+    /// Error message if publish failed.
+    /// </summary>
+    public string? Error { get; init; }
+}
+
+/// <summary>
+/// Publisher for EPSS signals to the notification system.
+/// Routes signals to the appropriate topics based on event type.
+/// </summary>
+public interface IEpssSignalPublisher
+{
+    /// <summary>
+    /// Topic name for EPSS signals.
+    /// </summary>
+    const string TopicName = "signals.epss";
+
+    /// <summary>
+    /// Publishes an EPSS signal to the notification system.
+    /// </summary>
+    /// <param name="signal">The signal to publish.</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>Result of the publish operation.</returns>
+    Task<EpssSignalPublishResult> PublishAsync(
+        EpssSignal signal,
+        CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Publishes multiple EPSS signals in a batch.
+    /// </summary>
+    /// <param name="signals">The signals to publish.</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>Number of successfully published signals.</returns>
+    Task<int> PublishBatchAsync(
+        IEnumerable<EpssSignal> signals,
+        CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Publishes a priority change event.
+    /// </summary>
+    /// <param name="tenantId">Tenant identifier.</param>
+    /// <param name="cveId">CVE identifier.</param>
+    /// <param name="oldBand">Previous priority band.</param>
+    /// <param name="newBand">New priority band.</param>
+    /// <param name="epssScore">Current EPSS score.</param>
+    /// <param name="modelDate">EPSS model date.</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>Result of the publish operation.</returns>
+    Task<EpssSignalPublishResult> PublishPriorityChangedAsync(
+        Guid tenantId,
+        string cveId,
+        string oldBand,
+        string newBand,
+        double epssScore,
+        DateOnly modelDate,
+        CancellationToken cancellationToken = default);
+}
+
+/// <summary>
+/// Null implementation of IEpssSignalPublisher for when messaging is disabled.
+/// </summary>
+public sealed class NullEpssSignalPublisher : IEpssSignalPublisher
+{
+    public static readonly NullEpssSignalPublisher Instance = new();
+
+    private NullEpssSignalPublisher() { }
+
+    public Task<EpssSignalPublishResult> PublishAsync(EpssSignal signal, CancellationToken cancellationToken = default)
+        => Task.FromResult(new EpssSignalPublishResult { Success = true, MessageId = "null" });
+
+    public Task<int> PublishBatchAsync(IEnumerable<EpssSignal> signals, CancellationToken cancellationToken = default)
+        => Task.FromResult(signals.Count());
+
+    public Task<EpssSignalPublishResult> PublishPriorityChangedAsync(
+        Guid tenantId, string cveId, string oldBand, string newBand, double epssScore, DateOnly modelDate,
+        CancellationToken cancellationToken = default)
+        => Task.FromResult(new EpssSignalPublishResult { Success = true, MessageId = "null" });
+}

src/Scanner/__Libraries/StellaOps.Scanner.Storage/Extensions/EpssServiceCollectionExtensions.cs

@@ -0,0 +1,165 @@
+// -----------------------------------------------------------------------------
+// EpssServiceCollectionExtensions.cs
+// Sprint: SPRINT_3410_0002_0001_epss_scanner_integration
+// Task: EPSS-SCAN-005
+// Description: DI registration for EPSS services with optional Valkey cache layer.
+// -----------------------------------------------------------------------------
+
+using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.DependencyInjection.Extensions;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Options;
+using StellaOps.Messaging.Abstractions;
+using StellaOps.Scanner.Core.Epss;
+using StellaOps.Scanner.Storage.Epss;
+using StellaOps.Scanner.Storage.Repositories;
+
+namespace StellaOps.Scanner.Storage.Extensions;
+
+/// <summary>
+/// Extension methods for registering EPSS services with optional Valkey caching.
+/// </summary>
+public static class EpssServiceCollectionExtensions
+{
+    /// <summary>
+    /// Adds EPSS provider services to the service collection.
+    /// Includes optional Valkey/Redis cache layer based on configuration.
+    /// </summary>
+    /// <param name="services">The service collection.</param>
+    /// <param name="configuration">The configuration section for EPSS options.</param>
+    /// <returns>The service collection for chaining.</returns>
+    public static IServiceCollection AddEpssProvider(
+        this IServiceCollection services,
+        IConfiguration configuration)
+    {
+        ArgumentNullException.ThrowIfNull(configuration);
+
+        // Bind EPSS provider options
+        services.AddOptions<EpssProviderOptions>()
+            .Bind(configuration.GetSection(EpssProviderOptions.SectionName))
+            .ValidateOnStart();
+
+        // Register the base PostgreSQL-backed provider
+        services.TryAddScoped<EpssProvider>();
+
+        // Register the caching decorator
+        services.TryAddScoped<IEpssProvider>(sp =>
+        {
+            var options = sp.GetRequiredService<IOptions<EpssProviderOptions>>().Value;
+            var innerProvider = sp.GetRequiredService<EpssProvider>();
+            var logger = sp.GetRequiredService<ILogger<CachingEpssProvider>>();
+            var timeProvider = sp.GetService<TimeProvider>() ?? TimeProvider.System;
+
+            // If caching is disabled, return the inner provider directly
+            if (!options.EnableCache)
+            {
+                return innerProvider;
+            }
+
+            // Try to get the cache factory (may be null if Valkey is not configured)
+            var cacheFactory = sp.GetService<IDistributedCacheFactory>();
+            IDistributedCache<EpssCacheEntry>? cache = null;
+
+            if (cacheFactory is not null)
+            {
+                try
+                {
+                    cache = cacheFactory.Create<EpssCacheEntry>(new CacheOptions
+                    {
+                        KeyPrefix = "epss:",
+                        DefaultTtl = options.CacheTtl,
+                        SlidingExpiration = false
+                    });
+                }
+                catch (Exception ex)
+                {
+                    logger.LogWarning(
+                        ex,
+                        "Failed to create EPSS cache, falling back to uncached provider. " +
+                        "Ensure Valkey/Redis is configured if caching is desired.");
+                }
+            }
+            else
+            {
+                logger.LogDebug(
+                    "No IDistributedCacheFactory registered. EPSS caching will be disabled. " +
+                    "Register StellaOps.Messaging.Transport.Valkey to enable caching.");
+            }
+
+            return new CachingEpssProvider(
+                innerProvider,
+                cache,
+                sp.GetRequiredService<IOptions<EpssProviderOptions>>(),
+                logger,
+                timeProvider);
+        });
+
+        return services;
+    }
+
+    /// <summary>
+    /// Adds EPSS provider services with explicit options configuration.
+    /// </summary>
+    /// <param name="services">The service collection.</param>
+    /// <param name="configure">The configuration action.</param>
+    /// <returns>The service collection for chaining.</returns>
+    public static IServiceCollection AddEpssProvider(
+        this IServiceCollection services,
+        Action<EpssProviderOptions> configure)
+    {
+        ArgumentNullException.ThrowIfNull(configure);
+
+        services.AddOptions<EpssProviderOptions>()
+            .Configure(configure)
+            .ValidateOnStart();
+
+        // Register the base PostgreSQL-backed provider
+        services.TryAddScoped<EpssProvider>();
+
+        // Register the caching decorator
+        services.TryAddScoped<IEpssProvider>(sp =>
+        {
+            var options = sp.GetRequiredService<IOptions<EpssProviderOptions>>().Value;
+            var innerProvider = sp.GetRequiredService<EpssProvider>();
+            var logger = sp.GetRequiredService<ILogger<CachingEpssProvider>>();
+            var timeProvider = sp.GetService<TimeProvider>() ?? TimeProvider.System;
+
+            // If caching is disabled, return the inner provider directly
+            if (!options.EnableCache)
+            {
+                return innerProvider;
+            }
+
+            // Try to get the cache factory
+            var cacheFactory = sp.GetService<IDistributedCacheFactory>();
+            IDistributedCache<EpssCacheEntry>? cache = null;
+
+            if (cacheFactory is not null)
+            {
+                try
+                {
+                    cache = cacheFactory.Create<EpssCacheEntry>(new CacheOptions
+                    {
+                        KeyPrefix = "epss:",
+                        DefaultTtl = options.CacheTtl,
+                        SlidingExpiration = false
+                    });
+                }
+                catch (Exception ex)
+                {
+                    logger.LogWarning(ex, "Failed to create EPSS cache");
+                }
+            }
+
+            return new CachingEpssProvider(
+                innerProvider,
+                cache,
+                sp.GetRequiredService<IOptions<EpssProviderOptions>>(),
+                logger,
+                timeProvider);
+        });
+
+        return services;
+    }
+}

src/Scanner/__Libraries/StellaOps.Scanner.Storage/Extensions/ServiceCollectionExtensions.cs

@@ -90,6 +90,22 @@ public static class ServiceCollectionExtensions
         services.AddSingleton<EpssBundleSource>();
         // Note: EpssChangeDetector is a static class, no DI registration needed
 
+        // EPSS provider with optional Valkey cache layer (Sprint: SPRINT_3410_0002_0001, Task: EPSS-SCAN-005)
+        services.AddEpssProvider(options =>
+        {
+            // Default configuration - can be overridden via config binding
+            options.EnableCache = true;
+            options.CacheTtl = TimeSpan.FromHours(1);
+            options.MaxBatchSize = 1000;
+        });
+
+        // EPSS raw and signal repositories (Sprint: SPRINT_3413_0001_0001)
+        services.AddScoped<IEpssRawRepository, PostgresEpssRawRepository>();
+        services.AddScoped<IEpssSignalRepository, PostgresEpssSignalRepository>();
+        services.AddScoped<IObservedCveRepository, PostgresObservedCveRepository>();
+        services.AddSingleton<EpssReplayService>();
+        services.TryAddSingleton<IEpssSignalPublisher, NullEpssSignalPublisher>();
+
         // Witness storage (Sprint: SPRINT_3700_0001_0001)
         services.AddScoped<IWitnessRepository, PostgresWitnessRepository>();
 

src/Scanner/__Libraries/StellaOps.Scanner.Storage/Postgres/Migrations/014_epss_triage_columns.sql

@@ -0,0 +1,150 @@
+-- SPDX-License-Identifier: AGPL-3.0-or-later
+-- Sprint: 3413
+-- Task: Task #2 - vuln_instance_triage schema updates
+-- Description: Adds EPSS tracking columns to vulnerability instance triage table
+
+-- ============================================================================
+-- EPSS Tracking Columns for Vulnerability Instances
+-- ============================================================================
+-- These columns store the current EPSS state for each vulnerability instance,
+-- enabling efficient priority band calculation and change detection.
+
+-- Add EPSS columns to vuln_instance_triage if table exists
+DO $$
+BEGIN
+    -- Check if table exists
+    IF EXISTS (SELECT 1 FROM information_schema.tables WHERE table_name = 'vuln_instance_triage') THEN
+        -- Add current_epss_score column
+        IF NOT EXISTS (SELECT 1 FROM information_schema.columns 
+                       WHERE table_name = 'vuln_instance_triage' AND column_name = 'current_epss_score') THEN
+            ALTER TABLE vuln_instance_triage ADD COLUMN current_epss_score DOUBLE PRECISION;
+            COMMENT ON COLUMN vuln_instance_triage.current_epss_score IS 'Current EPSS probability score [0,1]';
+        END IF;
+
+        -- Add current_epss_percentile column
+        IF NOT EXISTS (SELECT 1 FROM information_schema.columns 
+                       WHERE table_name = 'vuln_instance_triage' AND column_name = 'current_epss_percentile') THEN
+            ALTER TABLE vuln_instance_triage ADD COLUMN current_epss_percentile DOUBLE PRECISION;
+            COMMENT ON COLUMN vuln_instance_triage.current_epss_percentile IS 'Current EPSS percentile rank [0,1]';
+        END IF;
+
+        -- Add current_epss_band column
+        IF NOT EXISTS (SELECT 1 FROM information_schema.columns 
+                       WHERE table_name = 'vuln_instance_triage' AND column_name = 'current_epss_band') THEN
+            ALTER TABLE vuln_instance_triage ADD COLUMN current_epss_band TEXT;
+            COMMENT ON COLUMN vuln_instance_triage.current_epss_band IS 'Current EPSS priority band: CRITICAL, HIGH, MEDIUM, LOW';
+        END IF;
+
+        -- Add epss_model_date column
+        IF NOT EXISTS (SELECT 1 FROM information_schema.columns 
+                       WHERE table_name = 'vuln_instance_triage' AND column_name = 'epss_model_date') THEN
+            ALTER TABLE vuln_instance_triage ADD COLUMN epss_model_date DATE;
+            COMMENT ON COLUMN vuln_instance_triage.epss_model_date IS 'EPSS model date when last updated';
+        END IF;
+
+        -- Add epss_updated_at column
+        IF NOT EXISTS (SELECT 1 FROM information_schema.columns 
+                       WHERE table_name = 'vuln_instance_triage' AND column_name = 'epss_updated_at') THEN
+            ALTER TABLE vuln_instance_triage ADD COLUMN epss_updated_at TIMESTAMPTZ;
+            COMMENT ON COLUMN vuln_instance_triage.epss_updated_at IS 'Timestamp when EPSS data was last updated';
+        END IF;
+
+        -- Add previous_epss_band column (for change tracking)
+        IF NOT EXISTS (SELECT 1 FROM information_schema.columns 
+                       WHERE table_name = 'vuln_instance_triage' AND column_name = 'previous_epss_band') THEN
+            ALTER TABLE vuln_instance_triage ADD COLUMN previous_epss_band TEXT;
+            COMMENT ON COLUMN vuln_instance_triage.previous_epss_band IS 'Previous EPSS priority band before last update';
+        END IF;
+
+        -- Create index for efficient band-based queries
+        IF NOT EXISTS (SELECT 1 FROM pg_indexes WHERE indexname = 'idx_vuln_instance_epss_band') THEN
+            CREATE INDEX idx_vuln_instance_epss_band 
+                ON vuln_instance_triage (current_epss_band) 
+                WHERE current_epss_band IN ('CRITICAL', 'HIGH');
+        END IF;
+
+        -- Create index for stale EPSS data detection
+        IF NOT EXISTS (SELECT 1 FROM pg_indexes WHERE indexname = 'idx_vuln_instance_epss_model_date') THEN
+            CREATE INDEX idx_vuln_instance_epss_model_date 
+                ON vuln_instance_triage (epss_model_date);
+        END IF;
+
+        RAISE NOTICE 'Added EPSS columns to vuln_instance_triage table';
+    ELSE
+        RAISE NOTICE 'Table vuln_instance_triage does not exist; skipping EPSS column additions';
+    END IF;
+END $$;
+
+-- ============================================================================
+-- Batch Update Function for EPSS Enrichment
+-- ============================================================================
+-- Efficiently updates EPSS data for multiple vulnerability instances
+
+CREATE OR REPLACE FUNCTION batch_update_epss_triage(
+    p_updates JSONB,
+    p_model_date DATE,
+    p_updated_at TIMESTAMPTZ DEFAULT now()
+)
+RETURNS TABLE (
+    updated_count INT,
+    band_change_count INT
+) AS $$
+DECLARE
+    v_updated INT := 0;
+    v_band_changes INT := 0;
+    v_row RECORD;
+BEGIN
+    -- p_updates format: [{"instance_id": "...", "score": 0.123, "percentile": 0.456, "band": "HIGH"}, ...]
+    FOR v_row IN SELECT * FROM jsonb_to_recordset(p_updates) AS x(
+        instance_id UUID,
+        score DOUBLE PRECISION,
+        percentile DOUBLE PRECISION,
+        band TEXT
+    )
+    LOOP
+        UPDATE vuln_instance_triage SET
+            previous_epss_band = current_epss_band,
+            current_epss_score = v_row.score,
+            current_epss_percentile = v_row.percentile,
+            current_epss_band = v_row.band,
+            epss_model_date = p_model_date,
+            epss_updated_at = p_updated_at
+        WHERE instance_id = v_row.instance_id
+          AND (current_epss_band IS DISTINCT FROM v_row.band 
+               OR current_epss_score IS DISTINCT FROM v_row.score);
+
+        IF FOUND THEN
+            v_updated := v_updated + 1;
+            
+            -- Check if band actually changed
+            IF (SELECT previous_epss_band FROM vuln_instance_triage WHERE instance_id = v_row.instance_id)
+               IS DISTINCT FROM v_row.band THEN
+                v_band_changes := v_band_changes + 1;
+            END IF;
+        END IF;
+    END LOOP;
+
+    RETURN QUERY SELECT v_updated, v_band_changes;
+END;
+$$ LANGUAGE plpgsql;
+
+COMMENT ON FUNCTION batch_update_epss_triage IS 'Batch updates EPSS data for vulnerability instances, tracking band changes';
+
+-- ============================================================================
+-- View for Instances Needing EPSS Update
+-- ============================================================================
+-- Returns instances with stale or missing EPSS data
+
+CREATE OR REPLACE VIEW v_epss_stale_instances AS
+SELECT 
+    vit.instance_id,
+    vit.cve_id,
+    vit.tenant_id,
+    vit.current_epss_band,
+    vit.epss_model_date,
+    CURRENT_DATE - COALESCE(vit.epss_model_date, '1970-01-01'::DATE) AS days_stale
+FROM vuln_instance_triage vit
+WHERE vit.epss_model_date IS NULL 
+   OR vit.epss_model_date < CURRENT_DATE - 1;
+
+COMMENT ON VIEW v_epss_stale_instances IS 'Instances with stale or missing EPSS data, needing enrichment';

src/Scanner/__Libraries/StellaOps.Scanner.Storage/Postgres/Migrations/014_vuln_surfaces.sql

@@ -0,0 +1,177 @@
+-- =============================================================================
+-- Migration: 014_vuln_surfaces.sql
+-- Sprint: SPRINT_3700_0002_0001_vuln_surfaces_core
+-- Task: SURF-014
+-- Description: Vulnerability surface storage for trigger method analysis.
+-- =============================================================================
+
+BEGIN;
+
+-- Prevent re-running
+DO $$ BEGIN
+    IF EXISTS (SELECT 1 FROM pg_tables WHERE schemaname = 'scanner' AND tablename = 'vuln_surfaces') THEN
+        RAISE EXCEPTION 'Migration 014_vuln_surfaces already applied';
+    END IF;
+END $$;
+
+-- =============================================================================
+-- VULN_SURFACES: Computed vulnerability surface for CVE + package + version
+-- =============================================================================
+CREATE TABLE scanner.vuln_surfaces (
+    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    tenant_id UUID NOT NULL REFERENCES public.tenants(id),
+
+    -- CVE/vulnerability identity
+    cve_id TEXT NOT NULL,
+    package_ecosystem TEXT NOT NULL,  -- 'nuget', 'npm', 'maven', 'pypi'
+    package_name TEXT NOT NULL,
+    vuln_version TEXT NOT NULL,       -- Version with vulnerability
+    fixed_version TEXT,               -- First fixed version (null if no fix)
+
+    -- Surface computation metadata
+    computed_at TIMESTAMPTZ NOT NULL DEFAULT now(),
+    computation_duration_ms INTEGER,
+    fingerprint_method TEXT NOT NULL,  -- 'cecil-il', 'babel-ast', 'asm-bytecode', 'python-ast'
+
+    -- Summary statistics
+    total_methods_vuln INTEGER NOT NULL DEFAULT 0,
+    total_methods_fixed INTEGER NOT NULL DEFAULT 0,
+    changed_method_count INTEGER NOT NULL DEFAULT 0,
+
+    -- DSSE attestation (optional)
+    attestation_digest TEXT,
+
+    -- Indexes for lookups
+    CONSTRAINT uq_vuln_surface_key UNIQUE (tenant_id, cve_id, package_ecosystem, package_name, vuln_version)
+);
+
+-- Indexes for common queries
+CREATE INDEX idx_vuln_surfaces_cve ON scanner.vuln_surfaces(tenant_id, cve_id);
+CREATE INDEX idx_vuln_surfaces_package ON scanner.vuln_surfaces(tenant_id, package_ecosystem, package_name);
+CREATE INDEX idx_vuln_surfaces_computed_at ON scanner.vuln_surfaces(computed_at DESC);
+
+COMMENT ON TABLE scanner.vuln_surfaces IS 'Computed vulnerability surfaces identifying which methods changed between vulnerable and fixed versions';
+
+-- =============================================================================
+-- VULN_SURFACE_SINKS: Individual trigger methods for a vulnerability surface
+-- =============================================================================
+CREATE TABLE scanner.vuln_surface_sinks (
+    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    surface_id UUID NOT NULL REFERENCES scanner.vuln_surfaces(id) ON DELETE CASCADE,
+
+    -- Method identity
+    method_key TEXT NOT NULL,          -- Normalized method signature (FQN)
+    method_name TEXT NOT NULL,         -- Simple method name
+    declaring_type TEXT NOT NULL,      -- Containing class/module
+    namespace TEXT,                    -- Namespace/package
+
+    -- Change classification
+    change_type TEXT NOT NULL CHECK (change_type IN ('added', 'removed', 'modified')),
+
+    -- Fingerprints for comparison
+    vuln_fingerprint TEXT,             -- Hash in vulnerable version (null if added in fix)
+    fixed_fingerprint TEXT,            -- Hash in fixed version (null if removed in fix)
+
+    -- Metadata
+    is_public BOOLEAN NOT NULL DEFAULT true,
+    parameter_count INTEGER,
+    return_type TEXT,
+
+    -- Source location (if available from debug symbols)
+    source_file TEXT,
+    start_line INTEGER,
+    end_line INTEGER,
+
+    -- Indexes for lookups
+    CONSTRAINT uq_surface_sink_key UNIQUE (surface_id, method_key)
+);
+
+-- Indexes for common queries
+CREATE INDEX idx_vuln_surface_sinks_surface ON scanner.vuln_surface_sinks(surface_id);
+CREATE INDEX idx_vuln_surface_sinks_method ON scanner.vuln_surface_sinks(method_name);
+CREATE INDEX idx_vuln_surface_sinks_type ON scanner.vuln_surface_sinks(declaring_type);
+
+COMMENT ON TABLE scanner.vuln_surface_sinks IS 'Individual methods that changed between vulnerable and fixed package versions';
+
+-- =============================================================================
+-- VULN_SURFACE_TRIGGERS: Links sinks to call graph nodes where they are invoked
+-- =============================================================================
+CREATE TABLE scanner.vuln_surface_triggers (
+    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    sink_id UUID NOT NULL REFERENCES scanner.vuln_surface_sinks(id) ON DELETE CASCADE,
+    scan_id UUID NOT NULL,             -- References scanner.scans
+
+    -- Caller identity
+    caller_node_id TEXT NOT NULL,      -- Call graph node ID
+    caller_method_key TEXT NOT NULL,   -- FQN of calling method
+    caller_file TEXT,                  -- Source file of caller
+    caller_line INTEGER,               -- Line number of call
+
+    -- Reachability analysis
+    reachability_bucket TEXT NOT NULL DEFAULT 'unknown',  -- 'entrypoint', 'direct', 'runtime', 'unknown', 'unreachable'
+    path_length INTEGER,               -- Shortest path from entrypoint
+    confidence REAL NOT NULL DEFAULT 0.5,
+
+    -- Evidence
+    call_type TEXT NOT NULL DEFAULT 'direct',  -- 'direct', 'virtual', 'interface', 'reflection'
+    is_conditional BOOLEAN NOT NULL DEFAULT false,
+
+    -- Indexes for lookups
+    CONSTRAINT uq_trigger_key UNIQUE (sink_id, scan_id, caller_node_id)
+);
+
+-- Indexes for common queries
+CREATE INDEX idx_vuln_surface_triggers_sink ON scanner.vuln_surface_triggers(sink_id);
+CREATE INDEX idx_vuln_surface_triggers_scan ON scanner.vuln_surface_triggers(scan_id);
+CREATE INDEX idx_vuln_surface_triggers_bucket ON scanner.vuln_surface_triggers(reachability_bucket);
+
+COMMENT ON TABLE scanner.vuln_surface_triggers IS 'Links between vulnerability sink methods and their callers in analyzed code';
+
+-- =============================================================================
+-- RLS (Row Level Security)
+-- =============================================================================
+ALTER TABLE scanner.vuln_surfaces ENABLE ROW LEVEL SECURITY;
+
+-- Tenant isolation policy
+CREATE POLICY vuln_surfaces_tenant_isolation ON scanner.vuln_surfaces
+    USING (tenant_id = current_setting('app.tenant_id', true)::uuid);
+
+-- Note: vuln_surface_sinks and triggers inherit isolation through FK to surfaces
+
+-- =============================================================================
+-- FUNCTIONS
+-- =============================================================================
+
+-- Get surface statistics for a CVE
+CREATE OR REPLACE FUNCTION scanner.get_vuln_surface_stats(
+    p_tenant_id UUID,
+    p_cve_id TEXT
+)
+RETURNS TABLE (
+    package_ecosystem TEXT,
+    package_name TEXT,
+    vuln_version TEXT,
+    fixed_version TEXT,
+    changed_method_count INTEGER,
+    trigger_count BIGINT
+) AS $$
+BEGIN
+    RETURN QUERY
+    SELECT
+        vs.package_ecosystem,
+        vs.package_name,
+        vs.vuln_version,
+        vs.fixed_version,
+        vs.changed_method_count,
+        COUNT(DISTINCT vst.id)::BIGINT AS trigger_count
+    FROM scanner.vuln_surfaces vs
+    LEFT JOIN scanner.vuln_surface_sinks vss ON vss.surface_id = vs.id
+    LEFT JOIN scanner.vuln_surface_triggers vst ON vst.sink_id = vss.id
+    WHERE vs.tenant_id = p_tenant_id
+      AND vs.cve_id = p_cve_id
+    GROUP BY vs.id, vs.package_ecosystem, vs.package_name, vs.vuln_version, vs.fixed_version, vs.changed_method_count
+    ORDER BY vs.package_ecosystem, vs.package_name;
+END;
+$$ LANGUAGE plpgsql STABLE;
+
+COMMIT;

src/Scanner/__Libraries/StellaOps.Scanner.Storage/Postgres/Migrations/MigrationIds.cs

@@ -15,4 +15,6 @@ internal static class MigrationIds
     public const string EpssRawLayer = "011_epss_raw_layer.sql";
     public const string EpssSignalLayer = "012_epss_signal_layer.sql";
     public const string WitnessStorage = "013_witness_storage.sql";
+    public const string EpssTriageColumns = "014_epss_triage_columns.sql";
 }
+

src/Scanner/__Libraries/StellaOps.Scanner.Storage/Postgres/PostgresEpssRawRepository.cs

@@ -0,0 +1,228 @@
+// -----------------------------------------------------------------------------
+// PostgresEpssRawRepository.cs
+// Sprint: SPRINT_3413_0001_0001_epss_live_enrichment
+// Task: R1-R4 - EPSS Raw Feed Layer
+// Description: PostgreSQL implementation of IEpssRawRepository.
+// -----------------------------------------------------------------------------
+
+using Dapper;
+using StellaOps.Scanner.Storage.Repositories;
+
+namespace StellaOps.Scanner.Storage.Postgres;
+
+/// <summary>
+/// PostgreSQL implementation of <see cref="IEpssRawRepository"/>.
+/// </summary>
+public sealed class PostgresEpssRawRepository : IEpssRawRepository
+{
+    private readonly ScannerDataSource _dataSource;
+
+    private string SchemaName => _dataSource.SchemaName ?? ScannerDataSource.DefaultSchema;
+    private string RawTable => $"{SchemaName}.epss_raw";
+
+    public PostgresEpssRawRepository(ScannerDataSource dataSource)
+    {
+        _dataSource = dataSource ?? throw new ArgumentNullException(nameof(dataSource));
+    }
+
+    public async Task<EpssRaw> CreateAsync(EpssRaw raw, CancellationToken cancellationToken = default)
+    {
+        ArgumentNullException.ThrowIfNull(raw);
+
+        var sql = $"""
+            INSERT INTO {RawTable} (
+                source_uri, asof_date, payload, payload_sha256,
+                header_comment, model_version, published_date,
+                row_count, compressed_size, decompressed_size, import_run_id
+            )
+            VALUES (
+                @SourceUri, @AsOfDate, @Payload::jsonb, @PayloadSha256,
+                @HeaderComment, @ModelVersion, @PublishedDate,
+                @RowCount, @CompressedSize, @DecompressedSize, @ImportRunId
+            )
+            ON CONFLICT (source_uri, asof_date, payload_sha256) DO NOTHING
+            RETURNING raw_id, ingestion_ts
+            """;
+
+        await using var connection = await _dataSource.OpenConnectionAsync(cancellationToken);
+
+        var result = await connection.QueryFirstOrDefaultAsync<(long raw_id, DateTimeOffset ingestion_ts)?>(sql, new
+        {
+            raw.SourceUri,
+            AsOfDate = raw.AsOfDate.ToDateTime(TimeOnly.MinValue),
+            raw.Payload,
+            raw.PayloadSha256,
+            raw.HeaderComment,
+            raw.ModelVersion,
+            PublishedDate = raw.PublishedDate?.ToDateTime(TimeOnly.MinValue),
+            raw.RowCount,
+            raw.CompressedSize,
+            raw.DecompressedSize,
+            raw.ImportRunId
+        });
+
+        if (result.HasValue)
+        {
+            return raw with
+            {
+                RawId = result.Value.raw_id,
+                IngestionTs = result.Value.ingestion_ts
+            };
+        }
+
+        // Record already exists (idempotency), fetch existing
+        var existing = await GetByDateAsync(raw.AsOfDate, cancellationToken);
+        return existing ?? raw;
+    }
+
+    public async Task<EpssRaw?> GetByDateAsync(DateOnly asOfDate, CancellationToken cancellationToken = default)
+    {
+        var sql = $"""
+            SELECT
+                raw_id, source_uri, asof_date, ingestion_ts,
+                payload, payload_sha256, header_comment, model_version, published_date,
+                row_count, compressed_size, decompressed_size, import_run_id
+            FROM {RawTable}
+            WHERE asof_date = @AsOfDate
+            ORDER BY ingestion_ts DESC
+            LIMIT 1
+            """;
+
+        await using var connection = await _dataSource.OpenConnectionAsync(cancellationToken);
+        var row = await connection.QueryFirstOrDefaultAsync<RawRow?>(sql, new
+        {
+            AsOfDate = asOfDate.ToDateTime(TimeOnly.MinValue)
+        });
+
+        return row.HasValue ? MapToRaw(row.Value) : null;
+    }
+
+    public async Task<IReadOnlyList<EpssRaw>> GetByDateRangeAsync(
+        DateOnly startDate,
+        DateOnly endDate,
+        CancellationToken cancellationToken = default)
+    {
+        var sql = $"""
+            SELECT
+                raw_id, source_uri, asof_date, ingestion_ts,
+                payload, payload_sha256, header_comment, model_version, published_date,
+                row_count, compressed_size, decompressed_size, import_run_id
+            FROM {RawTable}
+            WHERE asof_date >= @StartDate AND asof_date <= @EndDate
+            ORDER BY asof_date DESC
+            """;
+
+        await using var connection = await _dataSource.OpenConnectionAsync(cancellationToken);
+        var rows = await connection.QueryAsync<RawRow>(sql, new
+        {
+            StartDate = startDate.ToDateTime(TimeOnly.MinValue),
+            EndDate = endDate.ToDateTime(TimeOnly.MinValue)
+        });
+
+        return rows.Select(MapToRaw).ToList();
+    }
+
+    public async Task<EpssRaw?> GetLatestAsync(CancellationToken cancellationToken = default)
+    {
+        var sql = $"""
+            SELECT
+                raw_id, source_uri, asof_date, ingestion_ts,
+                payload, payload_sha256, header_comment, model_version, published_date,
+                row_count, compressed_size, decompressed_size, import_run_id
+            FROM {RawTable}
+            ORDER BY asof_date DESC, ingestion_ts DESC
+            LIMIT 1
+            """;
+
+        await using var connection = await _dataSource.OpenConnectionAsync(cancellationToken);
+        var row = await connection.QueryFirstOrDefaultAsync<RawRow?>(sql);
+
+        return row.HasValue ? MapToRaw(row.Value) : null;
+    }
+
+    public async Task<bool> ExistsAsync(DateOnly asOfDate, byte[] payloadSha256, CancellationToken cancellationToken = default)
+    {
+        var sql = $"""
+            SELECT EXISTS (
+                SELECT 1 FROM {RawTable}
+                WHERE asof_date = @AsOfDate AND payload_sha256 = @PayloadSha256
+            )
+            """;
+
+        await using var connection = await _dataSource.OpenConnectionAsync(cancellationToken);
+        return await connection.ExecuteScalarAsync<bool>(sql, new
+        {
+            AsOfDate = asOfDate.ToDateTime(TimeOnly.MinValue),
+            PayloadSha256 = payloadSha256
+        });
+    }
+
+    public async Task<IReadOnlyList<EpssRaw>> GetByModelVersionAsync(
+        string modelVersion,
+        int limit = 100,
+        CancellationToken cancellationToken = default)
+    {
+        var sql = $"""
+            SELECT
+                raw_id, source_uri, asof_date, ingestion_ts,
+                payload, payload_sha256, header_comment, model_version, published_date,
+                row_count, compressed_size, decompressed_size, import_run_id
+            FROM {RawTable}
+            WHERE model_version = @ModelVersion
+            ORDER BY asof_date DESC
+            LIMIT @Limit
+            """;
+
+        await using var connection = await _dataSource.OpenConnectionAsync(cancellationToken);
+        var rows = await connection.QueryAsync<RawRow>(sql, new
+        {
+            ModelVersion = modelVersion,
+            Limit = limit
+        });
+
+        return rows.Select(MapToRaw).ToList();
+    }
+
+    public async Task<int> PruneAsync(int retentionDays = 365, CancellationToken cancellationToken = default)
+    {
+        var sql = $"SELECT {SchemaName}.prune_epss_raw(@RetentionDays)";
+
+        await using var connection = await _dataSource.OpenConnectionAsync(cancellationToken);
+        return await connection.ExecuteScalarAsync<int>(sql, new { RetentionDays = retentionDays });
+    }
+
+    private static EpssRaw MapToRaw(RawRow row)
+    {
+        return new EpssRaw
+        {
+            RawId = row.raw_id,
+            SourceUri = row.source_uri,
+            AsOfDate = DateOnly.FromDateTime(row.asof_date),
+            IngestionTs = row.ingestion_ts,
+            Payload = row.payload,
+            PayloadSha256 = row.payload_sha256,
+            HeaderComment = row.header_comment,
+            ModelVersion = row.model_version,
+            PublishedDate = row.published_date.HasValue ? DateOnly.FromDateTime(row.published_date.Value) : null,
+            RowCount = row.row_count,
+            CompressedSize = row.compressed_size,
+            DecompressedSize = row.decompressed_size,
+            ImportRunId = row.import_run_id
+        };
+    }
+
+    private readonly record struct RawRow(
+        long raw_id,
+        string source_uri,
+        DateTime asof_date,
+        DateTimeOffset ingestion_ts,
+        string payload,
+        byte[] payload_sha256,
+        string? header_comment,
+        string? model_version,
+        DateTime? published_date,
+        int row_count,
+        long? compressed_size,
+        long? decompressed_size,
+        Guid? import_run_id);
+}

src/Scanner/__Libraries/StellaOps.Scanner.Storage/Postgres/PostgresEpssRepository.cs

@@ -9,6 +9,7 @@ using System.Data;
 using Dapper;
 using Npgsql;
 using NpgsqlTypes;
+using StellaOps.Scanner.Core.Epss;
 using StellaOps.Scanner.Storage.Epss;
 using StellaOps.Scanner.Storage.Repositories;
 
@@ -481,6 +482,61 @@ public sealed class PostgresEpssRepository : IEpssRepository
             cancellationToken: cancellationToken)).ConfigureAwait(false);
     }
 
+    /// <inheritdoc />
+    public async Task<IReadOnlyList<EpssChangeRecord>> GetChangesAsync(
+        DateOnly modelDate,
+        Core.Epss.EpssChangeFlags? flags = null,
+        int limit = 100000,
+        CancellationToken cancellationToken = default)
+    {
+        var sql = $"""
+            SELECT
+                cve_id,
+                flags,
+                prev_score,
+                new_score,
+                new_percentile,
+                prev_band,
+                model_date
+            FROM {ChangesTable}
+            WHERE model_date = @ModelDate
+            {(flags.HasValue ? "AND (flags & @Flags) != 0" : "")}
+            ORDER BY new_score DESC
+            LIMIT @Limit
+            """;
+
+        await using var connection = await _dataSource.OpenConnectionAsync(cancellationToken);
+
+        var rows = await connection.QueryAsync<ChangeRow>(sql, new
+        {
+            ModelDate = modelDate,
+            Flags = flags.HasValue ? (int)flags.Value : 0,
+            Limit = limit
+        });
+
+        return rows.Select(r => new EpssChangeRecord
+        {
+            CveId = r.cve_id,
+            Flags = (Core.Epss.EpssChangeFlags)r.flags,
+            PreviousScore = r.prev_score,
+            NewScore = r.new_score,
+            NewPercentile = r.new_percentile,
+            PreviousBand = (Core.Epss.EpssPriorityBand)r.prev_band,
+            ModelDate = r.model_date
+        }).ToList();
+    }
+
+    private sealed class ChangeRow
+    {
+        public string cve_id { get; set; } = "";
+        public int flags { get; set; }
+        public double? prev_score { get; set; }
+        public double new_score { get; set; }
+        public double new_percentile { get; set; }
+        public int prev_band { get; set; }
+        public DateOnly model_date { get; set; }
+    }
+
     private sealed class StageCounts
     {
         public int distinct_count { get; set; }

src/Scanner/__Libraries/StellaOps.Scanner.Storage/Postgres/PostgresEpssSignalRepository.cs

@@ -0,0 +1,395 @@
+// -----------------------------------------------------------------------------
+// PostgresEpssSignalRepository.cs
+// Sprint: SPRINT_3413_0001_0001_epss_live_enrichment
+// Task: S3 - Implement PostgresEpssSignalRepository
+// Description: PostgreSQL implementation of IEpssSignalRepository.
+// -----------------------------------------------------------------------------
+
+using System.Text.Json;
+using Dapper;
+using StellaOps.Scanner.Storage.Repositories;
+
+namespace StellaOps.Scanner.Storage.Postgres;
+
+/// <summary>
+/// PostgreSQL implementation of <see cref="IEpssSignalRepository"/>.
+/// </summary>
+public sealed class PostgresEpssSignalRepository : IEpssSignalRepository
+{
+    private readonly ScannerDataSource _dataSource;
+
+    private string SchemaName => _dataSource.SchemaName ?? ScannerDataSource.DefaultSchema;
+    private string SignalTable => $"{SchemaName}.epss_signal";
+    private string ConfigTable => $"{SchemaName}.epss_signal_config";
+
+    public PostgresEpssSignalRepository(ScannerDataSource dataSource)
+    {
+        _dataSource = dataSource ?? throw new ArgumentNullException(nameof(dataSource));
+    }
+
+    public async Task<EpssSignal> CreateAsync(EpssSignal signal, CancellationToken cancellationToken = default)
+    {
+        ArgumentNullException.ThrowIfNull(signal);
+
+        var sql = $"""
+            INSERT INTO {SignalTable} (
+                tenant_id, model_date, cve_id, event_type, risk_band,
+                epss_score, epss_delta, percentile, percentile_delta,
+                is_model_change, model_version, dedupe_key, explain_hash, payload
+            )
+            VALUES (
+                @TenantId, @ModelDate, @CveId, @EventType, @RiskBand,
+                @EpssScore, @EpssDelta, @Percentile, @PercentileDelta,
+                @IsModelChange, @ModelVersion, @DedupeKey, @ExplainHash, @Payload::jsonb
+            )
+            ON CONFLICT (tenant_id, dedupe_key) DO NOTHING
+            RETURNING signal_id, created_at
+            """;
+
+        await using var connection = await _dataSource.OpenConnectionAsync(cancellationToken);
+
+        var result = await connection.QueryFirstOrDefaultAsync<(long signal_id, DateTimeOffset created_at)?>(sql, new
+        {
+            signal.TenantId,
+            ModelDate = signal.ModelDate.ToDateTime(TimeOnly.MinValue),
+            signal.CveId,
+            signal.EventType,
+            signal.RiskBand,
+            signal.EpssScore,
+            signal.EpssDelta,
+            signal.Percentile,
+            signal.PercentileDelta,
+            signal.IsModelChange,
+            signal.ModelVersion,
+            signal.DedupeKey,
+            signal.ExplainHash,
+            signal.Payload
+        });
+
+        if (result.HasValue)
+        {
+            return signal with
+            {
+                SignalId = result.Value.signal_id,
+                CreatedAt = result.Value.created_at
+            };
+        }
+
+        // Signal already exists (dedupe), fetch existing
+        var existing = await GetByDedupeKeyAsync(signal.TenantId, signal.DedupeKey, cancellationToken);
+        return existing ?? signal;
+    }
+
+    public async Task<int> CreateBulkAsync(IEnumerable<EpssSignal> signals, CancellationToken cancellationToken = default)
+    {
+        ArgumentNullException.ThrowIfNull(signals);
+
+        var signalList = signals.ToList();
+        if (signalList.Count == 0)
+        {
+            return 0;
+        }
+
+        var sql = $"""
+            INSERT INTO {SignalTable} (
+                tenant_id, model_date, cve_id, event_type, risk_band,
+                epss_score, epss_delta, percentile, percentile_delta,
+                is_model_change, model_version, dedupe_key, explain_hash, payload
+            )
+            VALUES (
+                @TenantId, @ModelDate, @CveId, @EventType, @RiskBand,
+                @EpssScore, @EpssDelta, @Percentile, @PercentileDelta,
+                @IsModelChange, @ModelVersion, @DedupeKey, @ExplainHash, @Payload::jsonb
+            )
+            ON CONFLICT (tenant_id, dedupe_key) DO NOTHING
+            """;
+
+        await using var connection = await _dataSource.OpenConnectionAsync(cancellationToken);
+        await using var transaction = await connection.BeginTransactionAsync(cancellationToken);
+
+        var inserted = 0;
+        foreach (var signal in signalList)
+        {
+            var affected = await connection.ExecuteAsync(sql, new
+            {
+                signal.TenantId,
+                ModelDate = signal.ModelDate.ToDateTime(TimeOnly.MinValue),
+                signal.CveId,
+                signal.EventType,
+                signal.RiskBand,
+                signal.EpssScore,
+                signal.EpssDelta,
+                signal.Percentile,
+                signal.PercentileDelta,
+                signal.IsModelChange,
+                signal.ModelVersion,
+                signal.DedupeKey,
+                signal.ExplainHash,
+                signal.Payload
+            }, transaction);
+
+            inserted += affected;
+        }
+
+        await transaction.CommitAsync(cancellationToken);
+        return inserted;
+    }
+
+    public async Task<IReadOnlyList<EpssSignal>> GetByTenantAsync(
+        Guid tenantId,
+        DateOnly startDate,
+        DateOnly endDate,
+        IEnumerable<string>? eventTypes = null,
+        CancellationToken cancellationToken = default)
+    {
+        var eventTypeList = eventTypes?.ToList();
+        var hasEventTypeFilter = eventTypeList?.Count > 0;
+
+        var sql = $"""
+            SELECT
+                signal_id, tenant_id, model_date, cve_id, event_type, risk_band,
+                epss_score, epss_delta, percentile, percentile_delta,
+                is_model_change, model_version, dedupe_key, explain_hash, payload, created_at
+            FROM {SignalTable}
+            WHERE tenant_id = @TenantId
+              AND model_date >= @StartDate
+              AND model_date <= @EndDate
+              {(hasEventTypeFilter ? "AND event_type = ANY(@EventTypes)" : "")}
+            ORDER BY model_date DESC, created_at DESC
+            LIMIT 10000
+            """;
+
+        await using var connection = await _dataSource.OpenConnectionAsync(cancellationToken);
+
+        var rows = await connection.QueryAsync<SignalRow>(sql, new
+        {
+            TenantId = tenantId,
+            StartDate = startDate.ToDateTime(TimeOnly.MinValue),
+            EndDate = endDate.ToDateTime(TimeOnly.MinValue),
+            EventTypes = eventTypeList?.ToArray()
+        });
+
+        return rows.Select(MapToSignal).ToList();
+    }
+
+    public async Task<IReadOnlyList<EpssSignal>> GetByCveAsync(
+        Guid tenantId,
+        string cveId,
+        int limit = 100,
+        CancellationToken cancellationToken = default)
+    {
+        var sql = $"""
+            SELECT
+                signal_id, tenant_id, model_date, cve_id, event_type, risk_band,
+                epss_score, epss_delta, percentile, percentile_delta,
+                is_model_change, model_version, dedupe_key, explain_hash, payload, created_at
+            FROM {SignalTable}
+            WHERE tenant_id = @TenantId
+              AND cve_id = @CveId
+            ORDER BY model_date DESC, created_at DESC
+            LIMIT @Limit
+            """;
+
+        await using var connection = await _dataSource.OpenConnectionAsync(cancellationToken);
+
+        var rows = await connection.QueryAsync<SignalRow>(sql, new
+        {
+            TenantId = tenantId,
+            CveId = cveId,
+            Limit = limit
+        });
+
+        return rows.Select(MapToSignal).ToList();
+    }
+
+    public async Task<IReadOnlyList<EpssSignal>> GetHighPriorityAsync(
+        Guid tenantId,
+        DateOnly startDate,
+        DateOnly endDate,
+        CancellationToken cancellationToken = default)
+    {
+        var sql = $"""
+            SELECT
+                signal_id, tenant_id, model_date, cve_id, event_type, risk_band,
+                epss_score, epss_delta, percentile, percentile_delta,
+                is_model_change, model_version, dedupe_key, explain_hash, payload, created_at
+            FROM {SignalTable}
+            WHERE tenant_id = @TenantId
+              AND model_date >= @StartDate
+              AND model_date <= @EndDate
+              AND risk_band IN ('CRITICAL', 'HIGH')
+            ORDER BY model_date DESC, created_at DESC
+            LIMIT 10000
+            """;
+
+        await using var connection = await _dataSource.OpenConnectionAsync(cancellationToken);
+
+        var rows = await connection.QueryAsync<SignalRow>(sql, new
+        {
+            TenantId = tenantId,
+            StartDate = startDate.ToDateTime(TimeOnly.MinValue),
+            EndDate = endDate.ToDateTime(TimeOnly.MinValue)
+        });
+
+        return rows.Select(MapToSignal).ToList();
+    }
+
+    public async Task<EpssSignalConfig?> GetConfigAsync(Guid tenantId, CancellationToken cancellationToken = default)
+    {
+        var sql = $"""
+            SELECT
+                config_id, tenant_id,
+                critical_percentile, high_percentile, medium_percentile,
+                big_jump_delta, suppress_on_model_change, enabled_event_types,
+                created_at, updated_at
+            FROM {ConfigTable}
+            WHERE tenant_id = @TenantId
+            """;
+
+        await using var connection = await _dataSource.OpenConnectionAsync(cancellationToken);
+
+        var row = await connection.QueryFirstOrDefaultAsync<ConfigRow?>(sql, new { TenantId = tenantId });
+
+        return row.HasValue ? MapToConfig(row.Value) : null;
+    }
+
+    public async Task<EpssSignalConfig> UpsertConfigAsync(EpssSignalConfig config, CancellationToken cancellationToken = default)
+    {
+        ArgumentNullException.ThrowIfNull(config);
+
+        var sql = $"""
+            INSERT INTO {ConfigTable} (
+                tenant_id, critical_percentile, high_percentile, medium_percentile,
+                big_jump_delta, suppress_on_model_change, enabled_event_types
+            )
+            VALUES (
+                @TenantId, @CriticalPercentile, @HighPercentile, @MediumPercentile,
+                @BigJumpDelta, @SuppressOnModelChange, @EnabledEventTypes
+            )
+            ON CONFLICT (tenant_id) DO UPDATE SET
+                critical_percentile = EXCLUDED.critical_percentile,
+                high_percentile = EXCLUDED.high_percentile,
+                medium_percentile = EXCLUDED.medium_percentile,
+                big_jump_delta = EXCLUDED.big_jump_delta,
+                suppress_on_model_change = EXCLUDED.suppress_on_model_change,
+                enabled_event_types = EXCLUDED.enabled_event_types,
+                updated_at = now()
+            RETURNING config_id, created_at, updated_at
+            """;
+
+        await using var connection = await _dataSource.OpenConnectionAsync(cancellationToken);
+
+        var result = await connection.QueryFirstAsync<(Guid config_id, DateTimeOffset created_at, DateTimeOffset updated_at)>(sql, new
+        {
+            config.TenantId,
+            config.CriticalPercentile,
+            config.HighPercentile,
+            config.MediumPercentile,
+            config.BigJumpDelta,
+            config.SuppressOnModelChange,
+            EnabledEventTypes = config.EnabledEventTypes.ToArray()
+        });
+
+        return config with
+        {
+            ConfigId = result.config_id,
+            CreatedAt = result.created_at,
+            UpdatedAt = result.updated_at
+        };
+    }
+
+    public async Task<int> PruneAsync(int retentionDays = 90, CancellationToken cancellationToken = default)
+    {
+        var sql = $"SELECT {SchemaName}.prune_epss_signals(@RetentionDays)";
+
+        await using var connection = await _dataSource.OpenConnectionAsync(cancellationToken);
+        return await connection.ExecuteScalarAsync<int>(sql, new { RetentionDays = retentionDays });
+    }
+
+    private async Task<EpssSignal?> GetByDedupeKeyAsync(Guid tenantId, string dedupeKey, CancellationToken cancellationToken)
+    {
+        var sql = $"""
+            SELECT
+                signal_id, tenant_id, model_date, cve_id, event_type, risk_band,
+                epss_score, epss_delta, percentile, percentile_delta,
+                is_model_change, model_version, dedupe_key, explain_hash, payload, created_at
+            FROM {SignalTable}
+            WHERE tenant_id = @TenantId AND dedupe_key = @DedupeKey
+            """;
+
+        await using var connection = await _dataSource.OpenConnectionAsync(cancellationToken);
+        var row = await connection.QueryFirstOrDefaultAsync<SignalRow?>(sql, new { TenantId = tenantId, DedupeKey = dedupeKey });
+
+        return row.HasValue ? MapToSignal(row.Value) : null;
+    }
+
+    private static EpssSignal MapToSignal(SignalRow row)
+    {
+        return new EpssSignal
+        {
+            SignalId = row.signal_id,
+            TenantId = row.tenant_id,
+            ModelDate = DateOnly.FromDateTime(row.model_date),
+            CveId = row.cve_id,
+            EventType = row.event_type,
+            RiskBand = row.risk_band,
+            EpssScore = row.epss_score,
+            EpssDelta = row.epss_delta,
+            Percentile = row.percentile,
+            PercentileDelta = row.percentile_delta,
+            IsModelChange = row.is_model_change,
+            ModelVersion = row.model_version,
+            DedupeKey = row.dedupe_key,
+            ExplainHash = row.explain_hash,
+            Payload = row.payload,
+            CreatedAt = row.created_at
+        };
+    }
+
+    private static EpssSignalConfig MapToConfig(ConfigRow row)
+    {
+        return new EpssSignalConfig
+        {
+            ConfigId = row.config_id,
+            TenantId = row.tenant_id,
+            CriticalPercentile = row.critical_percentile,
+            HighPercentile = row.high_percentile,
+            MediumPercentile = row.medium_percentile,
+            BigJumpDelta = row.big_jump_delta,
+            SuppressOnModelChange = row.suppress_on_model_change,
+            EnabledEventTypes = row.enabled_event_types ?? Array.Empty<string>(),
+            CreatedAt = row.created_at,
+            UpdatedAt = row.updated_at
+        };
+    }
+
+    private readonly record struct SignalRow(
+        long signal_id,
+        Guid tenant_id,
+        DateTime model_date,
+        string cve_id,
+        string event_type,
+        string? risk_band,
+        double? epss_score,
+        double? epss_delta,
+        double? percentile,
+        double? percentile_delta,
+        bool is_model_change,
+        string? model_version,
+        string dedupe_key,
+        byte[] explain_hash,
+        string payload,
+        DateTimeOffset created_at);
+
+    private readonly record struct ConfigRow(
+        Guid config_id,
+        Guid tenant_id,
+        double critical_percentile,
+        double high_percentile,
+        double medium_percentile,
+        double big_jump_delta,
+        bool suppress_on_model_change,
+        string[]? enabled_event_types,
+        DateTimeOffset created_at,
+        DateTimeOffset updated_at);
+}

src/Scanner/__Libraries/StellaOps.Scanner.Storage/Postgres/PostgresObservedCveRepository.cs

@@ -0,0 +1,152 @@
+// -----------------------------------------------------------------------------
+// PostgresObservedCveRepository.cs
+// Sprint: SPRINT_3413_0001_0001_epss_live_enrichment
+// Task: S6 - Add observed CVEs filter
+// Description: PostgreSQL implementation of IObservedCveRepository.
+// -----------------------------------------------------------------------------
+
+using Dapper;
+using StellaOps.Scanner.Storage.Repositories;
+
+namespace StellaOps.Scanner.Storage.Postgres;
+
+/// <summary>
+/// PostgreSQL implementation of <see cref="IObservedCveRepository"/>.
+/// Queries vuln_instance_triage to determine which CVEs are observed per tenant.
+/// </summary>
+public sealed class PostgresObservedCveRepository : IObservedCveRepository
+{
+    private readonly ScannerDataSource _dataSource;
+
+    private string SchemaName => _dataSource.SchemaName ?? ScannerDataSource.DefaultSchema;
+    private string TriageTable => $"{SchemaName}.vuln_instance_triage";
+
+    public PostgresObservedCveRepository(ScannerDataSource dataSource)
+    {
+        _dataSource = dataSource ?? throw new ArgumentNullException(nameof(dataSource));
+    }
+
+    public async Task<IReadOnlySet<string>> GetObservedCvesAsync(
+        Guid tenantId,
+        CancellationToken cancellationToken = default)
+    {
+        var sql = $"""
+            SELECT DISTINCT cve_id
+            FROM {TriageTable}
+            WHERE tenant_id = @TenantId
+              AND cve_id IS NOT NULL
+              AND cve_id LIKE 'CVE-%'
+            """;
+
+        await using var connection = await _dataSource.OpenConnectionAsync(cancellationToken);
+        var cves = await connection.QueryAsync<string>(sql, new { TenantId = tenantId });
+
+        return new HashSet<string>(cves, StringComparer.OrdinalIgnoreCase);
+    }
+
+    public async Task<bool> IsObservedAsync(
+        Guid tenantId,
+        string cveId,
+        CancellationToken cancellationToken = default)
+    {
+        var sql = $"""
+            SELECT EXISTS (
+                SELECT 1 FROM {TriageTable}
+                WHERE tenant_id = @TenantId
+                  AND cve_id = @CveId
+            )
+            """;
+
+        await using var connection = await _dataSource.OpenConnectionAsync(cancellationToken);
+        return await connection.ExecuteScalarAsync<bool>(sql, new { TenantId = tenantId, CveId = cveId });
+    }
+
+    public async Task<IReadOnlySet<string>> FilterObservedAsync(
+        Guid tenantId,
+        IEnumerable<string> cveIds,
+        CancellationToken cancellationToken = default)
+    {
+        var cveList = cveIds.ToList();
+        if (cveList.Count == 0)
+        {
+            return new HashSet<string>(StringComparer.OrdinalIgnoreCase);
+        }
+
+        var sql = $"""
+            SELECT DISTINCT cve_id
+            FROM {TriageTable}
+            WHERE tenant_id = @TenantId
+              AND cve_id = ANY(@CveIds)
+            """;
+
+        await using var connection = await _dataSource.OpenConnectionAsync(cancellationToken);
+        var observed = await connection.QueryAsync<string>(sql, new
+        {
+            TenantId = tenantId,
+            CveIds = cveList.ToArray()
+        });
+
+        return new HashSet<string>(observed, StringComparer.OrdinalIgnoreCase);
+    }
+
+    public async Task<IReadOnlyList<Guid>> GetActiveTenantsAsync(
+        CancellationToken cancellationToken = default)
+    {
+        var sql = $"""
+            SELECT DISTINCT tenant_id
+            FROM {TriageTable}
+            WHERE cve_id IS NOT NULL
+              AND cve_id LIKE 'CVE-%'
+            """;
+
+        await using var connection = await _dataSource.OpenConnectionAsync(cancellationToken);
+        var tenants = await connection.QueryAsync<Guid>(sql);
+
+        return tenants.ToList();
+    }
+
+    public async Task<IReadOnlyDictionary<string, IReadOnlyList<Guid>>> GetTenantsObservingCvesAsync(
+        IEnumerable<string> cveIds,
+        CancellationToken cancellationToken = default)
+    {
+        var cveList = cveIds.ToList();
+        if (cveList.Count == 0)
+        {
+            return new Dictionary<string, IReadOnlyList<Guid>>(StringComparer.OrdinalIgnoreCase);
+        }
+
+        var sql = $"""
+            SELECT cve_id, tenant_id
+            FROM {TriageTable}
+            WHERE cve_id = ANY(@CveIds)
+            GROUP BY cve_id, tenant_id
+            """;
+
+        await using var connection = await _dataSource.OpenConnectionAsync(cancellationToken);
+        var rows = await connection.QueryAsync<(string cve_id, Guid tenant_id)>(sql, new
+        {
+            CveIds = cveList.ToArray()
+        });
+
+        var result = new Dictionary<string, List<Guid>>(StringComparer.OrdinalIgnoreCase);
+
+        foreach (var row in rows)
+        {
+            if (!result.TryGetValue(row.cve_id, out var tenants))
+            {
+                tenants = new List<Guid>();
+                result[row.cve_id] = tenants;
+            }
+
+            if (!tenants.Contains(row.tenant_id))
+            {
+                tenants.Add(row.tenant_id);
+            }
+        }
+
+        return result.ToDictionary(
+            kvp => kvp.Key,
+            kvp => (IReadOnlyList<Guid>)kvp.Value,
+            StringComparer.OrdinalIgnoreCase);
+    }
+}

src/Scanner/__Libraries/StellaOps.Scanner.Storage/Repositories/IEpssRawRepository.cs

@@ -0,0 +1,152 @@
+// -----------------------------------------------------------------------------
+// IEpssRawRepository.cs
+// Sprint: SPRINT_3413_0001_0001_epss_live_enrichment
+// Task: R1-R4 - EPSS Raw Feed Layer
+// Description: Repository interface for immutable EPSS raw payload storage.
+// -----------------------------------------------------------------------------
+
+namespace StellaOps.Scanner.Storage.Repositories;
+
+/// <summary>
+/// Repository for immutable EPSS raw payload storage.
+/// Layer 1 of the 3-layer EPSS architecture: stores full CSV payload as JSONB.
+/// </summary>
+public interface IEpssRawRepository
+{
+    /// <summary>
+    /// Stores a raw EPSS payload.
+    /// </summary>
+    /// <param name="raw">The raw payload to store.</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>The stored record with generated ID.</returns>
+    Task<EpssRaw> CreateAsync(EpssRaw raw, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Gets a raw payload by as-of date.
+    /// </summary>
+    /// <param name="asOfDate">The date of the EPSS snapshot.</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>The raw payload, or null if not found.</returns>
+    Task<EpssRaw?> GetByDateAsync(DateOnly asOfDate, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Gets raw payloads within a date range.
+    /// </summary>
+    /// <param name="startDate">Start date (inclusive).</param>
+    /// <param name="endDate">End date (inclusive).</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>List of raw payloads ordered by date descending.</returns>
+    Task<IReadOnlyList<EpssRaw>> GetByDateRangeAsync(
+        DateOnly startDate,
+        DateOnly endDate,
+        CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Gets the most recent raw payload.
+    /// </summary>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>The most recent raw payload, or null if none exist.</returns>
+    Task<EpssRaw?> GetLatestAsync(CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Checks if a raw payload exists for a given date and content hash.
+    /// Used for idempotency checks.
+    /// </summary>
+    /// <param name="asOfDate">The date of the EPSS snapshot.</param>
+    /// <param name="payloadSha256">SHA-256 hash of decompressed content.</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>True if the payload already exists.</returns>
+    Task<bool> ExistsAsync(DateOnly asOfDate, byte[] payloadSha256, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Gets payloads by model version.
+    /// Useful for detecting model version changes.
+    /// </summary>
+    /// <param name="modelVersion">The model version string.</param>
+    /// <param name="limit">Maximum number of records to return.</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>List of raw payloads with the specified model version.</returns>
+    Task<IReadOnlyList<EpssRaw>> GetByModelVersionAsync(
+        string modelVersion,
+        int limit = 100,
+        CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Prunes old raw payloads based on retention policy.
+    /// </summary>
+    /// <param name="retentionDays">Number of days to retain. Default: 365.</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>Number of records deleted.</returns>
+    Task<int> PruneAsync(int retentionDays = 365, CancellationToken cancellationToken = default);
+}
+
+/// <summary>
+/// EPSS raw payload entity.
+/// </summary>
+public sealed record EpssRaw
+{
+    /// <summary>
+    /// Raw record ID (auto-generated).
+    /// </summary>
+    public long RawId { get; init; }
+
+    /// <summary>
+    /// Source URI where the data was retrieved from.
+    /// </summary>
+    public required string SourceUri { get; init; }
+
+    /// <summary>
+    /// Date of the EPSS snapshot.
+    /// </summary>
+    public required DateOnly AsOfDate { get; init; }
+
+    /// <summary>
+    /// Timestamp when the data was ingested.
+    /// </summary>
+    public DateTimeOffset IngestionTs { get; init; }
+
+    /// <summary>
+    /// Full payload as JSON array: [{cve:"CVE-...", epss:0.123, percentile:0.456}, ...].
+    /// </summary>
+    public required string Payload { get; init; }
+
+    /// <summary>
+    /// SHA-256 hash of decompressed content for integrity verification.
+    /// </summary>
+    public required byte[] PayloadSha256 { get; init; }
+
+    /// <summary>
+    /// Raw comment line from CSV header (e.g., "# model: v2025.03.14, published: 2025-03-14").
+    /// </summary>
+    public string? HeaderComment { get; init; }
+
+    /// <summary>
+    /// Extracted model version from header comment.
+    /// </summary>
+    public string? ModelVersion { get; init; }
+
+    /// <summary>
+    /// Extracted publish date from header comment.
+    /// </summary>
+    public DateOnly? PublishedDate { get; init; }
+
+    /// <summary>
+    /// Number of rows in the payload.
+    /// </summary>
+    public required int RowCount { get; init; }
+
+    /// <summary>
+    /// Original compressed file size (bytes).
+    /// </summary>
+    public long? CompressedSize { get; init; }
+
+    /// <summary>
+    /// Decompressed CSV size (bytes).
+    /// </summary>
+    public long? DecompressedSize { get; init; }
+
+    /// <summary>
+    /// Reference to the import run that created this record.
+    /// </summary>
+    public Guid? ImportRunId { get; init; }
+}

src/Scanner/__Libraries/StellaOps.Scanner.Storage/Repositories/IEpssRepository.cs

@@ -5,6 +5,7 @@
 // Description: EPSS persistence contract (import runs, scores/current projection, change log).
 // -----------------------------------------------------------------------------
 
+using StellaOps.Scanner.Core.Epss;
 using StellaOps.Scanner.Storage.Epss;
 
 namespace StellaOps.Scanner.Storage.Repositories;
@@ -54,6 +55,21 @@ public interface IEpssRepository
         string cveId,
         int days,
         CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Gets EPSS change records for a model date, optionally filtered by flags.
+    /// Used by enrichment job to target only CVEs with material changes.
+    /// </summary>
+    /// <param name="modelDate">The EPSS model date.</param>
+    /// <param name="flags">Change flags to filter by. Null returns all changes.</param>
+    /// <param name="limit">Maximum number of records to return.</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>List of change records matching the criteria.</returns>
+    Task<IReadOnlyList<EpssChangeRecord>> GetChangesAsync(
+        DateOnly modelDate,
+        EpssChangeFlags? flags = null,
+        int limit = 100000,
+        CancellationToken cancellationToken = default);
 }
 
 public sealed record EpssImportRun(

src/Scanner/__Libraries/StellaOps.Scanner.Storage/Repositories/IEpssSignalRepository.cs

@@ -0,0 +1,242 @@
+// -----------------------------------------------------------------------------
+// IEpssSignalRepository.cs
+// Sprint: SPRINT_3413_0001_0001_epss_live_enrichment
+// Task: S2 - Implement IEpssSignalRepository interface
+// Description: Repository interface for EPSS signal-ready events.
+// -----------------------------------------------------------------------------
+
+namespace StellaOps.Scanner.Storage.Repositories;
+
+/// <summary>
+/// Repository for EPSS signal-ready events (tenant-scoped).
+/// </summary>
+public interface IEpssSignalRepository
+{
+    /// <summary>
+    /// Creates a new EPSS signal.
+    /// </summary>
+    /// <param name="signal">The signal to create.</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>The created signal with generated ID.</returns>
+    Task<EpssSignal> CreateAsync(EpssSignal signal, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Creates multiple EPSS signals in bulk.
+    /// Uses upsert with dedupe_key to prevent duplicates.
+    /// </summary>
+    /// <param name="signals">The signals to create.</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>Number of signals created (excluding duplicates).</returns>
+    Task<int> CreateBulkAsync(IEnumerable<EpssSignal> signals, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Gets signals for a tenant within a date range.
+    /// </summary>
+    /// <param name="tenantId">Tenant identifier.</param>
+    /// <param name="startDate">Start date (inclusive).</param>
+    /// <param name="endDate">End date (inclusive).</param>
+    /// <param name="eventTypes">Optional filter by event types.</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>List of signals ordered by model_date descending.</returns>
+    Task<IReadOnlyList<EpssSignal>> GetByTenantAsync(
+        Guid tenantId,
+        DateOnly startDate,
+        DateOnly endDate,
+        IEnumerable<string>? eventTypes = null,
+        CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Gets signals for a specific CVE within a tenant.
+    /// </summary>
+    /// <param name="tenantId">Tenant identifier.</param>
+    /// <param name="cveId">CVE identifier.</param>
+    /// <param name="limit">Maximum number of signals to return.</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>List of signals ordered by model_date descending.</returns>
+    Task<IReadOnlyList<EpssSignal>> GetByCveAsync(
+        Guid tenantId,
+        string cveId,
+        int limit = 100,
+        CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Gets high-priority signals (CRITICAL/HIGH band) for a tenant.
+    /// </summary>
+    /// <param name="tenantId">Tenant identifier.</param>
+    /// <param name="startDate">Start date (inclusive).</param>
+    /// <param name="endDate">End date (inclusive).</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>List of high-priority signals.</returns>
+    Task<IReadOnlyList<EpssSignal>> GetHighPriorityAsync(
+        Guid tenantId,
+        DateOnly startDate,
+        DateOnly endDate,
+        CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Gets the signal configuration for a tenant.
+    /// </summary>
+    /// <param name="tenantId">Tenant identifier.</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>The configuration, or null if not configured.</returns>
+    Task<EpssSignalConfig?> GetConfigAsync(Guid tenantId, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Upserts the signal configuration for a tenant.
+    /// </summary>
+    /// <param name="config">The configuration to upsert.</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>The upserted configuration.</returns>
+    Task<EpssSignalConfig> UpsertConfigAsync(EpssSignalConfig config, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Prunes old signals based on retention policy.
+    /// </summary>
+    /// <param name="retentionDays">Number of days to retain. Default: 90.</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>Number of signals deleted.</returns>
+    Task<int> PruneAsync(int retentionDays = 90, CancellationToken cancellationToken = default);
+}
+
+/// <summary>
+/// EPSS signal entity.
+/// </summary>
+public sealed record EpssSignal
+{
+    /// <summary>
+    /// Signal ID (auto-generated).
+    /// </summary>
+    public long SignalId { get; init; }
+
+    /// <summary>
+    /// Tenant identifier.
+    /// </summary>
+    public required Guid TenantId { get; init; }
+
+    /// <summary>
+    /// EPSS model date.
+    /// </summary>
+    public required DateOnly ModelDate { get; init; }
+
+    /// <summary>
+    /// CVE identifier.
+    /// </summary>
+    public required string CveId { get; init; }
+
+    /// <summary>
+    /// Event type: RISK_SPIKE, BAND_CHANGE, NEW_HIGH, DROPPED_LOW, MODEL_UPDATED.
+    /// </summary>
+    public required string EventType { get; init; }
+
+    /// <summary>
+    /// Risk band: CRITICAL, HIGH, MEDIUM, LOW.
+    /// </summary>
+    public string? RiskBand { get; init; }
+
+    /// <summary>
+    /// EPSS score at signal time.
+    /// </summary>
+    public double? EpssScore { get; init; }
+
+    /// <summary>
+    /// EPSS score delta from previous day.
+    /// </summary>
+    public double? EpssDelta { get; init; }
+
+    /// <summary>
+    /// EPSS percentile at signal time.
+    /// </summary>
+    public double? Percentile { get; init; }
+
+    /// <summary>
+    /// Percentile delta from previous day.
+    /// </summary>
+    public double? PercentileDelta { get; init; }
+
+    /// <summary>
+    /// Whether this is a model version change day.
+    /// </summary>
+    public bool IsModelChange { get; init; }
+
+    /// <summary>
+    /// EPSS model version.
+    /// </summary>
+    public string? ModelVersion { get; init; }
+
+    /// <summary>
+    /// Deterministic deduplication key.
+    /// </summary>
+    public required string DedupeKey { get; init; }
+
+    /// <summary>
+    /// SHA-256 of signal inputs for audit trail.
+    /// </summary>
+    public required byte[] ExplainHash { get; init; }
+
+    /// <summary>
+    /// Full evidence payload as JSON.
+    /// </summary>
+    public required string Payload { get; init; }
+
+    /// <summary>
+    /// Creation timestamp.
+    /// </summary>
+    public DateTimeOffset CreatedAt { get; init; }
+}
+
+/// <summary>
+/// EPSS signal configuration for a tenant.
+/// </summary>
+public sealed record EpssSignalConfig
+{
+    /// <summary>
+    /// Configuration ID.
+    /// </summary>
+    public Guid ConfigId { get; init; }
+
+    /// <summary>
+    /// Tenant identifier.
+    /// </summary>
+    public required Guid TenantId { get; init; }
+
+    /// <summary>
+    /// Critical percentile threshold. Default: 0.995.
+    /// </summary>
+    public double CriticalPercentile { get; init; } = 0.995;
+
+    /// <summary>
+    /// High percentile threshold. Default: 0.99.
+    /// </summary>
+    public double HighPercentile { get; init; } = 0.99;
+
+    /// <summary>
+    /// Medium percentile threshold. Default: 0.90.
+    /// </summary>
+    public double MediumPercentile { get; init; } = 0.90;
+
+    /// <summary>
+    /// Big jump delta threshold. Default: 0.10.
+    /// </summary>
+    public double BigJumpDelta { get; init; } = 0.10;
+
+    /// <summary>
+    /// Suppress signals on model version change. Default: true.
+    /// </summary>
+    public bool SuppressOnModelChange { get; init; } = true;
+
+    /// <summary>
+    /// Enabled event types.
+    /// </summary>
+    public IReadOnlyList<string> EnabledEventTypes { get; init; } =
+        new[] { "RISK_SPIKE", "BAND_CHANGE", "NEW_HIGH" };
+
+    /// <summary>
+    /// Creation timestamp.
+    /// </summary>
+    public DateTimeOffset CreatedAt { get; init; }
+
+    /// <summary>
+    /// Last update timestamp.
+    /// </summary>
+    public DateTimeOffset UpdatedAt { get; init; }
+}

src/Scanner/__Libraries/StellaOps.Scanner.Storage/Repositories/IObservedCveRepository.cs

@@ -0,0 +1,101 @@
+// -----------------------------------------------------------------------------
+// IObservedCveRepository.cs
+// Sprint: SPRINT_3413_0001_0001_epss_live_enrichment
+// Task: S6 - Add observed CVEs filter
+// Description: Repository interface for tracking observed CVEs per tenant.
+// -----------------------------------------------------------------------------
+
+namespace StellaOps.Scanner.Storage.Repositories;
+
+/// <summary>
+/// Repository for tracking which CVEs are observed (in use) by each tenant.
+/// Used to filter EPSS signals to only relevant CVEs.
+/// </summary>
+public interface IObservedCveRepository
+{
+    /// <summary>
+    /// Gets the set of CVE IDs that are currently observed by a tenant.
+    /// Only CVEs that exist in the tenant's vulnerability inventory.
+    /// </summary>
+    /// <param name="tenantId">Tenant identifier.</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>Set of observed CVE IDs.</returns>
+    Task<IReadOnlySet<string>> GetObservedCvesAsync(
+        Guid tenantId,
+        CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Checks if a CVE is observed by a tenant.
+    /// </summary>
+    /// <param name="tenantId">Tenant identifier.</param>
+    /// <param name="cveId">CVE identifier.</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>True if the CVE is observed.</returns>
+    Task<bool> IsObservedAsync(
+        Guid tenantId,
+        string cveId,
+        CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Filters a set of CVE IDs to only those observed by a tenant.
+    /// </summary>
+    /// <param name="tenantId">Tenant identifier.</param>
+    /// <param name="cveIds">CVE IDs to filter.</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>Filtered set of observed CVE IDs.</returns>
+    Task<IReadOnlySet<string>> FilterObservedAsync(
+        Guid tenantId,
+        IEnumerable<string> cveIds,
+        CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Gets all tenant IDs that have at least one observed CVE.
+    /// </summary>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>List of tenant IDs.</returns>
+    Task<IReadOnlyList<Guid>> GetActiveTenantsAsync(
+        CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Gets tenant IDs that observe specific CVEs.
+    /// Used for targeted signal delivery.
+    /// </summary>
+    /// <param name="cveIds">CVE IDs to check.</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>Dictionary mapping CVE ID to list of tenant IDs observing it.</returns>
+    Task<IReadOnlyDictionary<string, IReadOnlyList<Guid>>> GetTenantsObservingCvesAsync(
+        IEnumerable<string> cveIds,
+        CancellationToken cancellationToken = default);
+}
+
+/// <summary>
+/// Null implementation of IObservedCveRepository for when tenant filtering is disabled.
+/// Returns all CVEs as observed.
+/// </summary>
+public sealed class NullObservedCveRepository : IObservedCveRepository
+{
+    public static readonly NullObservedCveRepository Instance = new();
+
+    private NullObservedCveRepository() { }
+
+    public Task<IReadOnlySet<string>> GetObservedCvesAsync(Guid tenantId, CancellationToken cancellationToken = default)
+        => Task.FromResult<IReadOnlySet<string>>(new HashSet<string>(StringComparer.OrdinalIgnoreCase));
+
+    public Task<bool> IsObservedAsync(Guid tenantId, string cveId, CancellationToken cancellationToken = default)
+        => Task.FromResult(true); // All CVEs are observed when filtering is disabled
+
+    public Task<IReadOnlySet<string>> FilterObservedAsync(Guid tenantId, IEnumerable<string> cveIds, CancellationToken cancellationToken = default)
+        => Task.FromResult<IReadOnlySet<string>>(new HashSet<string>(cveIds, StringComparer.OrdinalIgnoreCase));
+
+    public Task<IReadOnlyList<Guid>> GetActiveTenantsAsync(CancellationToken cancellationToken = default)
+        => Task.FromResult<IReadOnlyList<Guid>>(new[] { Guid.Empty });
+
+    public Task<IReadOnlyDictionary<string, IReadOnlyList<Guid>>> GetTenantsObservingCvesAsync(IEnumerable<string> cveIds, CancellationToken cancellationToken = default)
+    {
+        var result = cveIds.ToDictionary(
+            cve => cve,
+            _ => (IReadOnlyList<Guid>)new[] { Guid.Empty },
+            StringComparer.OrdinalIgnoreCase);
+        return Task.FromResult<IReadOnlyDictionary<string, IReadOnlyList<Guid>>>(result);
+    }
+}

src/Scanner/__Libraries/StellaOps.Scanner.Storage/StellaOps.Scanner.Storage.csproj

@@ -27,5 +27,6 @@
     <ProjectReference Include="..\\StellaOps.Scanner.ReachabilityDrift\\StellaOps.Scanner.ReachabilityDrift.csproj" />
     <ProjectReference Include="..\\StellaOps.Scanner.SmartDiff\\StellaOps.Scanner.SmartDiff.csproj" />
     <ProjectReference Include="..\\..\\..\\__Libraries\\StellaOps.Infrastructure.Postgres\\StellaOps.Infrastructure.Postgres.csproj" />
+    <ProjectReference Include="..\\..\\..\\__Libraries\\StellaOps.Messaging\\StellaOps.Messaging.csproj" />
   </ItemGroup>
 </Project>

src/Scanner/__Libraries/StellaOps.Scanner.VulnSurfaces.Tests/CecilMethodFingerprinterTests.cs

@@ -0,0 +1,197 @@
+// -----------------------------------------------------------------------------
+// CecilMethodFingerprinterTests.cs
+// Sprint: SPRINT_3700_0002_0001_vuln_surfaces_core
+// Description: Unit tests for CecilMethodFingerprinter.
+// -----------------------------------------------------------------------------
+
+using Microsoft.Extensions.Logging.Abstractions;
+using StellaOps.Scanner.VulnSurfaces.Fingerprint;
+using Xunit;
+
+namespace StellaOps.Scanner.VulnSurfaces.Tests;
+
+public class CecilMethodFingerprinterTests
+{
+    private readonly CecilMethodFingerprinter _fingerprinter;
+
+    public CecilMethodFingerprinterTests()
+    {
+        _fingerprinter = new CecilMethodFingerprinter(
+            NullLogger<CecilMethodFingerprinter>.Instance);
+    }
+
+    [Fact]
+    public void Ecosystem_ReturnsNuget()
+    {
+        Assert.Equal("nuget", _fingerprinter.Ecosystem);
+    }
+
+    [Fact]
+    public async Task FingerprintAsync_WithNullRequest_ThrowsArgumentNullException()
+    {
+        await Assert.ThrowsAsync<ArgumentNullException>(
+            () => _fingerprinter.FingerprintAsync(null!));
+    }
+
+    [Fact]
+    public async Task FingerprintAsync_WithNonExistentPath_ReturnsEmptyResult()
+    {
+        // Arrange
+        var request = new FingerprintRequest
+        {
+            PackagePath = "/nonexistent/path/to/package",
+            PackageName = "nonexistent",
+            Version = "1.0.0"
+        };
+
+        // Act
+        var result = await _fingerprinter.FingerprintAsync(request);
+
+        // Assert
+        Assert.NotNull(result);
+        Assert.True(result.Success);
+        Assert.Empty(result.Methods);
+    }
+
+    [Fact]
+    public async Task FingerprintAsync_WithOwnAssembly_FindsMethods()
+    {
+        // Arrange - use the test assembly itself
+        var testAssemblyPath = typeof(CecilMethodFingerprinterTests).Assembly.Location;
+        var assemblyDir = Path.GetDirectoryName(testAssemblyPath)!;
+
+        var request = new FingerprintRequest
+        {
+            PackagePath = assemblyDir,
+            PackageName = "test",
+            Version = "1.0.0",
+            IncludePrivateMethods = false
+        };
+
+        // Act
+        var result = await _fingerprinter.FingerprintAsync(request);
+
+        // Assert
+        Assert.NotNull(result);
+        Assert.True(result.Success);
+        Assert.NotEmpty(result.Methods);
+        
+        // Should find this test class
+        Assert.True(result.Methods.Count > 0, "Should find at least some methods");
+    }
+
+    [Fact]
+    public async Task FingerprintAsync_ComputesDeterministicHashes()
+    {
+        // Arrange - fingerprint twice
+        var testAssemblyPath = typeof(CecilMethodFingerprinterTests).Assembly.Location;
+        var assemblyDir = Path.GetDirectoryName(testAssemblyPath)!;
+
+        var request = new FingerprintRequest
+        {
+            PackagePath = assemblyDir,
+            PackageName = "test",
+            Version = "1.0.0",
+            IncludePrivateMethods = false
+        };
+
+        // Act
+        var result1 = await _fingerprinter.FingerprintAsync(request);
+        var result2 = await _fingerprinter.FingerprintAsync(request);
+
+        // Assert - same methods should produce same hashes
+        Assert.Equal(result1.Methods.Count, result2.Methods.Count);
+
+        foreach (var (key, fp1) in result1.Methods)
+        {
+            Assert.True(result2.Methods.TryGetValue(key, out var fp2));
+            Assert.Equal(fp1.BodyHash, fp2.BodyHash);
+        }
+    }
+
+    [Fact]
+    public async Task FingerprintAsync_WithCancellation_RespectsCancellation()
+    {
+        // Arrange
+        using var cts = new CancellationTokenSource();
+        cts.Cancel();
+
+        var testAssemblyPath = typeof(CecilMethodFingerprinterTests).Assembly.Location;
+        var assemblyDir = Path.GetDirectoryName(testAssemblyPath)!;
+
+        var request = new FingerprintRequest
+        {
+            PackagePath = assemblyDir,
+            PackageName = "test",
+            Version = "1.0.0"
+        };
+
+        // Act - operation may either throw or return early
+        // since the token is already cancelled
+        try
+        {
+            await _fingerprinter.FingerprintAsync(request, cts.Token);
+            // If it doesn't throw, that's also acceptable behavior
+            // The key is that it should respect the cancellation token
+            Assert.True(true, "Method completed without throwing - acceptable if it checks token");
+        }
+        catch (OperationCanceledException)
+        {
+            // Expected behavior
+            Assert.True(true);
+        }
+    }
+
+    [Fact]
+    public async Task FingerprintAsync_MethodKeyFormat_IsValid()
+    {
+        // Arrange
+        var testAssemblyPath = typeof(CecilMethodFingerprinterTests).Assembly.Location;
+        var assemblyDir = Path.GetDirectoryName(testAssemblyPath)!;
+
+        var request = new FingerprintRequest
+        {
+            PackagePath = assemblyDir,
+            PackageName = "test",
+            Version = "1.0.0",
+            IncludePrivateMethods = false
+        };
+
+        // Act
+        var result = await _fingerprinter.FingerprintAsync(request);
+
+        // Assert - keys should not be empty
+        foreach (var key in result.Methods.Keys)
+        {
+            Assert.NotEmpty(key);
+            // Method keys use "::" separator between type and method
+            // Some may be anonymous types like "<>f__AnonymousType0`2"
+            // Just verify they're non-empty and have reasonable format
+            Assert.True(key.Contains("::") || key.Contains("."),
+                $"Method key should contain :: or . separator: {key}");
+        }
+    }
+
+    [Fact]
+    public async Task FingerprintAsync_IncludesSignature()
+    {
+        // Arrange
+        var testAssemblyPath = typeof(CecilMethodFingerprinterTests).Assembly.Location;
+        var assemblyDir = Path.GetDirectoryName(testAssemblyPath)!;
+
+        var request = new FingerprintRequest
+        {
+            PackagePath = assemblyDir,
+            PackageName = "test",
+            Version = "1.0.0",
+            IncludePrivateMethods = false
+        };
+
+        // Act
+        var result = await _fingerprinter.FingerprintAsync(request);
+
+        // Assert - fingerprints should have signatures
+        var anyWithSignature = result.Methods.Values.Any(fp => !string.IsNullOrEmpty(fp.Signature));
+        Assert.True(anyWithSignature, "At least some methods should have signatures");
+    }
+}

src/Scanner/__Libraries/StellaOps.Scanner.VulnSurfaces.Tests/MethodDiffEngineTests.cs

@@ -0,0 +1,348 @@
+// -----------------------------------------------------------------------------
+// MethodDiffEngineTests.cs
+// Sprint: SPRINT_3700_0002_0001_vuln_surfaces_core
+// Description: Unit tests for MethodDiffEngine.
+// -----------------------------------------------------------------------------
+
+using Microsoft.Extensions.Logging.Abstractions;
+using StellaOps.Scanner.VulnSurfaces.Fingerprint;
+using Xunit;
+
+namespace StellaOps.Scanner.VulnSurfaces.Tests;
+
+public class MethodDiffEngineTests
+{
+    private readonly MethodDiffEngine _diffEngine;
+
+    public MethodDiffEngineTests()
+    {
+        _diffEngine = new MethodDiffEngine(
+            NullLogger<MethodDiffEngine>.Instance);
+    }
+
+    [Fact]
+    public async Task DiffAsync_WithNullRequest_ThrowsArgumentNullException()
+    {
+        await Assert.ThrowsAsync<ArgumentNullException>(
+            () => _diffEngine.DiffAsync(null!));
+    }
+
+    [Fact]
+    public async Task DiffAsync_WithIdenticalFingerprints_ReturnsNoChanges()
+    {
+        // Arrange
+        var fingerprint = CreateFingerprint("Test.Class::Method", "sha256:abc123");
+
+        var result1 = new FingerprintResult
+        {
+            Success = true,
+            Methods = new Dictionary<string, MethodFingerprint>
+            {
+                [fingerprint.MethodKey] = fingerprint
+            }
+        };
+
+        var result2 = new FingerprintResult
+        {
+            Success = true,
+            Methods = new Dictionary<string, MethodFingerprint>
+            {
+                [fingerprint.MethodKey] = fingerprint
+            }
+        };
+
+        var request = new MethodDiffRequest
+        {
+            VulnFingerprints = result1,
+            FixedFingerprints = result2
+        };
+
+        // Act
+        var diff = await _diffEngine.DiffAsync(request);
+
+        // Assert
+        Assert.True(diff.Success);
+        Assert.Empty(diff.Modified);
+        Assert.Empty(diff.Added);
+        Assert.Empty(diff.Removed);
+        Assert.Equal(0, diff.TotalChanges);
+    }
+
+    [Fact]
+    public async Task DiffAsync_WithModifiedMethod_ReturnsModified()
+    {
+        // Arrange
+        var vulnFp = CreateFingerprint("Test.Class::Method", "sha256:old_hash");
+        var fixedFp = CreateFingerprint("Test.Class::Method", "sha256:new_hash");
+
+        var vulnResult = new FingerprintResult
+        {
+            Success = true,
+            Methods = new Dictionary<string, MethodFingerprint>
+            {
+                [vulnFp.MethodKey] = vulnFp
+            }
+        };
+
+        var fixedResult = new FingerprintResult
+        {
+            Success = true,
+            Methods = new Dictionary<string, MethodFingerprint>
+            {
+                [fixedFp.MethodKey] = fixedFp
+            }
+        };
+
+        var request = new MethodDiffRequest
+        {
+            VulnFingerprints = vulnResult,
+            FixedFingerprints = fixedResult
+        };
+
+        // Act
+        var diff = await _diffEngine.DiffAsync(request);
+
+        // Assert
+        Assert.True(diff.Success);
+        Assert.Single(diff.Modified);
+        Assert.Equal("Test.Class::Method", diff.Modified[0].MethodKey);
+        Assert.Equal("sha256:old_hash", diff.Modified[0].VulnVersion.BodyHash);
+        Assert.Equal("sha256:new_hash", diff.Modified[0].FixedVersion.BodyHash);
+        Assert.Empty(diff.Added);
+        Assert.Empty(diff.Removed);
+    }
+
+    [Fact]
+    public async Task DiffAsync_WithAddedMethod_ReturnsAdded()
+    {
+        // Arrange
+        var vulnFp = CreateFingerprint("Test.Class::ExistingMethod", "sha256:existing");
+        var newFp = CreateFingerprint("Test.Class::NewMethod", "sha256:new_method");
+
+        var vulnResult = new FingerprintResult
+        {
+            Success = true,
+            Methods = new Dictionary<string, MethodFingerprint>
+            {
+                [vulnFp.MethodKey] = vulnFp
+            }
+        };
+
+        var fixedResult = new FingerprintResult
+        {
+            Success = true,
+            Methods = new Dictionary<string, MethodFingerprint>
+            {
+                [vulnFp.MethodKey] = vulnFp,
+                [newFp.MethodKey] = newFp
+            }
+        };
+
+        var request = new MethodDiffRequest
+        {
+            VulnFingerprints = vulnResult,
+            FixedFingerprints = fixedResult
+        };
+
+        // Act
+        var diff = await _diffEngine.DiffAsync(request);
+
+        // Assert
+        Assert.True(diff.Success);
+        Assert.Empty(diff.Modified);
+        Assert.Single(diff.Added);
+        Assert.Equal("Test.Class::NewMethod", diff.Added[0].MethodKey);
+        Assert.Empty(diff.Removed);
+    }
+
+    [Fact]
+    public async Task DiffAsync_WithRemovedMethod_ReturnsRemoved()
+    {
+        // Arrange
+        var existingFp = CreateFingerprint("Test.Class::ExistingMethod", "sha256:existing");
+        var removedFp = CreateFingerprint("Test.Class::RemovedMethod", "sha256:removed");
+
+        var vulnResult = new FingerprintResult
+        {
+            Success = true,
+            Methods = new Dictionary<string, MethodFingerprint>
+            {
+                [existingFp.MethodKey] = existingFp,
+                [removedFp.MethodKey] = removedFp
+            }
+        };
+
+        var fixedResult = new FingerprintResult
+        {
+            Success = true,
+            Methods = new Dictionary<string, MethodFingerprint>
+            {
+                [existingFp.MethodKey] = existingFp
+            }
+        };
+
+        var request = new MethodDiffRequest
+        {
+            VulnFingerprints = vulnResult,
+            FixedFingerprints = fixedResult
+        };
+
+        // Act
+        var diff = await _diffEngine.DiffAsync(request);
+
+        // Assert
+        Assert.True(diff.Success);
+        Assert.Empty(diff.Modified);
+        Assert.Empty(diff.Added);
+        Assert.Single(diff.Removed);
+        Assert.Equal("Test.Class::RemovedMethod", diff.Removed[0].MethodKey);
+    }
+
+    [Fact]
+    public async Task DiffAsync_WithMultipleChanges_ReturnsAllChanges()
+    {
+        // Arrange - simulate a fix that modifies one method, adds one, removes one
+        var unchangedFp = CreateFingerprint("Test::Unchanged", "h1");
+        var modifiedVuln = CreateFingerprint("Test::Modified", "old");
+        var modifiedFixed = CreateFingerprint("Test::Modified", "new");
+        var removedFp = CreateFingerprint("Test::Removed", "h2");
+        var addedFp = CreateFingerprint("Test::Added", "h3");
+
+        var vulnResult = new FingerprintResult
+        {
+            Success = true,
+            Methods = new Dictionary<string, MethodFingerprint>
+            {
+                [unchangedFp.MethodKey] = unchangedFp,
+                [modifiedVuln.MethodKey] = modifiedVuln,
+                [removedFp.MethodKey] = removedFp
+            }
+        };
+
+        var fixedResult = new FingerprintResult
+        {
+            Success = true,
+            Methods = new Dictionary<string, MethodFingerprint>
+            {
+                [unchangedFp.MethodKey] = unchangedFp,
+                [modifiedFixed.MethodKey] = modifiedFixed,
+                [addedFp.MethodKey] = addedFp
+            }
+        };
+
+        var request = new MethodDiffRequest
+        {
+            VulnFingerprints = vulnResult,
+            FixedFingerprints = fixedResult
+        };
+
+        // Act
+        var diff = await _diffEngine.DiffAsync(request);
+
+        // Assert
+        Assert.True(diff.Success);
+        Assert.Single(diff.Modified);
+        Assert.Single(diff.Added);
+        Assert.Single(diff.Removed);
+        Assert.Equal(3, diff.TotalChanges);
+    }
+
+    [Fact]
+    public async Task DiffAsync_TriggerMethods_AreModifiedOrRemoved()
+    {
+        // This test validates the key insight: 
+        // Trigger methods (the vulnerable entry points) are typically MODIFIED or REMOVED in a fix
+        // They wouldn't be ADDED in the fixed version
+        
+        // Arrange
+        var triggerMethodVuln = CreateFingerprint(
+            "Newtonsoft.Json.JsonConvert::DeserializeObject",
+            "sha256:vulnerable_impl");
+
+        var triggerMethodFixed = CreateFingerprint(
+            "Newtonsoft.Json.JsonConvert::DeserializeObject",
+            "sha256:patched_impl");
+
+        var vulnResult = new FingerprintResult
+        {
+            Success = true,
+            Methods = new Dictionary<string, MethodFingerprint>
+            {
+                [triggerMethodVuln.MethodKey] = triggerMethodVuln
+            }
+        };
+
+        var fixedResult = new FingerprintResult
+        {
+            Success = true,
+            Methods = new Dictionary<string, MethodFingerprint>
+            {
+                [triggerMethodFixed.MethodKey] = triggerMethodFixed
+            }
+        };
+
+        var request = new MethodDiffRequest
+        {
+            VulnFingerprints = vulnResult,
+            FixedFingerprints = fixedResult
+        };
+
+        // Act
+        var diff = await _diffEngine.DiffAsync(request);
+
+        // Assert - the trigger method should show as modified
+        Assert.True(diff.Success);
+        Assert.Single(diff.Modified);
+        Assert.Equal("Newtonsoft.Json.JsonConvert::DeserializeObject", diff.Modified[0].MethodKey);
+        Assert.Empty(diff.Added);
+        Assert.Empty(diff.Removed);
+    }
+
+    [Fact]
+    public async Task DiffAsync_WithEmptyFingerprints_ReturnsNoChanges()
+    {
+        // Arrange
+        var vulnResult = new FingerprintResult
+        {
+            Success = true,
+            Methods = new Dictionary<string, MethodFingerprint>()
+        };
+
+        var fixedResult = new FingerprintResult
+        {
+            Success = true,
+            Methods = new Dictionary<string, MethodFingerprint>()
+        };
+
+        var request = new MethodDiffRequest
+        {
+            VulnFingerprints = vulnResult,
+            FixedFingerprints = fixedResult
+        };
+
+        // Act
+        var diff = await _diffEngine.DiffAsync(request);
+
+        // Assert
+        Assert.True(diff.Success);
+        Assert.Equal(0, diff.TotalChanges);
+    }
+
+    private static MethodFingerprint CreateFingerprint(string methodKey, string bodyHash)
+    {
+        var parts = methodKey.Split("::");
+        var declaringType = parts.Length > 1 ? parts[0] : "Unknown";
+        var name = parts.Length > 1 ? parts[1] : parts[0];
+
+        return new MethodFingerprint
+        {
+            MethodKey = methodKey,
+            DeclaringType = declaringType,
+            Name = name,
+            BodyHash = bodyHash,
+            Signature = $"void {name}()",
+            IsPublic = true,
+            BodySize = 100
+        };
+    }
+}

src/Scanner/__Libraries/StellaOps.Scanner.VulnSurfaces.Tests/NuGetPackageDownloaderTests.cs

@@ -0,0 +1,362 @@
+// -----------------------------------------------------------------------------
+// NuGetPackageDownloaderTests.cs
+// Sprint: SPRINT_3700_0002_0001_vuln_surfaces_core
+// Task: SURF-020
+// Description: Unit tests for NuGetPackageDownloader.
+// -----------------------------------------------------------------------------
+
+using System.Net;
+using System.Text;
+using Microsoft.Extensions.Logging.Abstractions;
+using Microsoft.Extensions.Options;
+using Moq;
+using Moq.Protected;
+using StellaOps.Scanner.VulnSurfaces.Download;
+using Xunit;
+
+namespace StellaOps.Scanner.VulnSurfaces.Tests;
+
+public class NuGetPackageDownloaderTests : IDisposable
+{
+    private readonly string _testOutputDir;
+
+    public NuGetPackageDownloaderTests()
+    {
+        _testOutputDir = Path.Combine(Path.GetTempPath(), $"nuget-test-{Guid.NewGuid():N}");
+        Directory.CreateDirectory(_testOutputDir);
+    }
+
+    public void Dispose()
+    {
+        if (Directory.Exists(_testOutputDir))
+        {
+            try { Directory.Delete(_testOutputDir, recursive: true); }
+            catch { /* ignore cleanup failures */ }
+        }
+    }
+
+    [Fact]
+    public void Ecosystem_ReturnsNuget()
+    {
+        // Arrange
+        var downloader = CreateDownloader();
+
+        // Assert
+        Assert.Equal("nuget", downloader.Ecosystem);
+    }
+
+    [Fact]
+    public async Task DownloadAsync_WithNullRequest_ThrowsArgumentNullException()
+    {
+        // Arrange
+        var downloader = CreateDownloader();
+
+        // Act & Assert
+        await Assert.ThrowsAsync<ArgumentNullException>(
+            () => downloader.DownloadAsync(null!));
+    }
+
+    [Fact]
+    public async Task DownloadAsync_WithHttpError_ReturnsFailResult()
+    {
+        // Arrange
+        var mockHandler = new Mock<HttpMessageHandler>();
+        mockHandler
+            .Protected()
+            .Setup<Task<HttpResponseMessage>>(
+                "SendAsync",
+                ItExpr.IsAny<HttpRequestMessage>(),
+                ItExpr.IsAny<CancellationToken>())
+            .ReturnsAsync(new HttpResponseMessage
+            {
+                StatusCode = HttpStatusCode.NotFound,
+                ReasonPhrase = "Not Found"
+            });
+
+        var httpClient = new HttpClient(mockHandler.Object);
+        var downloader = CreateDownloader(httpClient);
+
+        var request = new PackageDownloadRequest
+        {
+            PackageName = "NonExistent.Package",
+            Version = "1.0.0",
+            OutputDirectory = _testOutputDir,
+            UseCache = false
+        };
+
+        // Act
+        var result = await downloader.DownloadAsync(request);
+
+        // Assert
+        Assert.False(result.Success);
+        Assert.Contains("404", result.Error ?? "");
+        Assert.Null(result.ExtractedPath);
+    }
+
+    [Fact]
+    public async Task DownloadAsync_WithValidNupkg_ReturnsSuccessResult()
+    {
+        // Arrange - create a mock .nupkg (which is just a zip file)
+        var nupkgContent = CreateMinimalNupkg();
+
+        var mockHandler = new Mock<HttpMessageHandler>();
+        mockHandler
+            .Protected()
+            .Setup<Task<HttpResponseMessage>>(
+                "SendAsync",
+                ItExpr.IsAny<HttpRequestMessage>(),
+                ItExpr.IsAny<CancellationToken>())
+            .ReturnsAsync(new HttpResponseMessage
+            {
+                StatusCode = HttpStatusCode.OK,
+                Content = new ByteArrayContent(nupkgContent)
+            });
+
+        var httpClient = new HttpClient(mockHandler.Object);
+        var downloader = CreateDownloader(httpClient);
+
+        var request = new PackageDownloadRequest
+        {
+            PackageName = "TestPackage",
+            Version = "1.0.0",
+            OutputDirectory = _testOutputDir,
+            UseCache = false
+        };
+
+        // Act
+        var result = await downloader.DownloadAsync(request);
+
+        // Assert
+        Assert.True(result.Success);
+        Assert.NotNull(result.ExtractedPath);
+        Assert.NotNull(result.ArchivePath);
+        Assert.True(Directory.Exists(result.ExtractedPath));
+        Assert.True(File.Exists(result.ArchivePath));
+        Assert.False(result.FromCache);
+    }
+
+    [Fact]
+    public async Task DownloadAsync_WithCachedPackage_ReturnsCachedResult()
+    {
+        // Arrange - pre-create the cached directory
+        var packageDir = Path.Combine(_testOutputDir, "testpackage.1.0.0");
+        Directory.CreateDirectory(packageDir);
+        File.WriteAllText(Path.Combine(packageDir, "marker.txt"), "cached");
+
+        var downloader = CreateDownloader();
+
+        var request = new PackageDownloadRequest
+        {
+            PackageName = "TestPackage",
+            Version = "1.0.0",
+            OutputDirectory = _testOutputDir,
+            UseCache = true
+        };
+
+        // Act
+        var result = await downloader.DownloadAsync(request);
+
+        // Assert
+        Assert.True(result.Success);
+        Assert.True(result.FromCache);
+        Assert.Equal(packageDir, result.ExtractedPath);
+    }
+
+    [Fact]
+    public async Task DownloadAsync_WithCacheFalse_BypassesCache()
+    {
+        // Arrange - pre-create the cached directory
+        var packageDir = Path.Combine(_testOutputDir, "testpackage.2.0.0");
+        Directory.CreateDirectory(packageDir);
+
+        // Set up mock to return content (we're bypassing cache)
+        var nupkgContent = CreateMinimalNupkg();
+        var mockHandler = new Mock<HttpMessageHandler>();
+        mockHandler
+            .Protected()
+            .Setup<Task<HttpResponseMessage>>(
+                "SendAsync",
+                ItExpr.IsAny<HttpRequestMessage>(),
+                ItExpr.IsAny<CancellationToken>())
+            .ReturnsAsync(new HttpResponseMessage
+            {
+                StatusCode = HttpStatusCode.OK,
+                Content = new ByteArrayContent(nupkgContent)
+            });
+
+        var httpClient = new HttpClient(mockHandler.Object);
+        var downloader = CreateDownloader(httpClient);
+
+        var request = new PackageDownloadRequest
+        {
+            PackageName = "TestPackage",
+            Version = "2.0.0",
+            OutputDirectory = _testOutputDir,
+            UseCache = false // Bypass cache
+        };
+
+        // Act
+        var result = await downloader.DownloadAsync(request);
+
+        // Assert
+        Assert.True(result.Success);
+        Assert.False(result.FromCache);
+        
+        // Verify HTTP call was made
+        mockHandler.Protected().Verify(
+            "SendAsync",
+            Times.Once(),
+            ItExpr.IsAny<HttpRequestMessage>(),
+            ItExpr.IsAny<CancellationToken>());
+    }
+
+    [Fact]
+    public async Task DownloadAsync_UsesCorrectUrl()
+    {
+        // Arrange
+        HttpRequestMessage? capturedRequest = null;
+
+        var mockHandler = new Mock<HttpMessageHandler>();
+        mockHandler
+            .Protected()
+            .Setup<Task<HttpResponseMessage>>(
+                "SendAsync",
+                ItExpr.IsAny<HttpRequestMessage>(),
+                ItExpr.IsAny<CancellationToken>())
+            .Callback<HttpRequestMessage, CancellationToken>((req, _) => capturedRequest = req)
+            .ReturnsAsync(new HttpResponseMessage
+            {
+                StatusCode = HttpStatusCode.NotFound
+            });
+
+        var httpClient = new HttpClient(mockHandler.Object);
+        var downloader = CreateDownloader(httpClient);
+
+        var request = new PackageDownloadRequest
+        {
+            PackageName = "Newtonsoft.Json",
+            Version = "13.0.3",
+            OutputDirectory = _testOutputDir,
+            UseCache = false
+        };
+
+        // Act
+        await downloader.DownloadAsync(request);
+
+        // Assert
+        Assert.NotNull(capturedRequest);
+        Assert.Contains("newtonsoft.json", capturedRequest.RequestUri!.ToString());
+        Assert.Contains("13.0.3", capturedRequest.RequestUri!.ToString());
+        Assert.EndsWith(".nupkg", capturedRequest.RequestUri!.ToString());
+    }
+
+    [Fact]
+    public async Task DownloadAsync_WithCustomRegistry_UsesCustomUrl()
+    {
+        // Arrange
+        HttpRequestMessage? capturedRequest = null;
+
+        var mockHandler = new Mock<HttpMessageHandler>();
+        mockHandler
+            .Protected()
+            .Setup<Task<HttpResponseMessage>>(
+                "SendAsync",
+                ItExpr.IsAny<HttpRequestMessage>(),
+                ItExpr.IsAny<CancellationToken>())
+            .Callback<HttpRequestMessage, CancellationToken>((req, _) => capturedRequest = req)
+            .ReturnsAsync(new HttpResponseMessage
+            {
+                StatusCode = HttpStatusCode.NotFound
+            });
+
+        var httpClient = new HttpClient(mockHandler.Object);
+        var downloader = CreateDownloader(httpClient);
+
+        var request = new PackageDownloadRequest
+        {
+            PackageName = "TestPackage",
+            Version = "1.0.0",
+            OutputDirectory = _testOutputDir,
+            RegistryUrl = "https://custom.nuget.feed.example.com/v3",
+            UseCache = false
+        };
+
+        // Act
+        await downloader.DownloadAsync(request);
+
+        // Assert
+        Assert.NotNull(capturedRequest);
+        Assert.StartsWith("https://custom.nuget.feed.example.com/v3", capturedRequest.RequestUri!.ToString());
+    }
+
+    [Fact]
+    public async Task DownloadAsync_WithCancellation_HonorsCancellation()
+    {
+        // Arrange
+        using var cts = new CancellationTokenSource();
+        cts.Cancel();
+
+        var mockHandler = new Mock<HttpMessageHandler>();
+        mockHandler
+            .Protected()
+            .Setup<Task<HttpResponseMessage>>(
+                "SendAsync",
+                ItExpr.IsAny<HttpRequestMessage>(),
+                ItExpr.IsAny<CancellationToken>())
+            .ThrowsAsync(new TaskCanceledException());
+
+        var httpClient = new HttpClient(mockHandler.Object);
+        var downloader = CreateDownloader(httpClient);
+
+        var request = new PackageDownloadRequest
+        {
+            PackageName = "TestPackage",
+            Version = "1.0.0",
+            OutputDirectory = _testOutputDir,
+            UseCache = false
+        };
+
+        // Act
+        var result = await downloader.DownloadAsync(request, cts.Token);
+
+        // Assert - should return failure, not throw
+        Assert.False(result.Success);
+        Assert.Contains("cancel", result.Error?.ToLower() ?? "");
+    }
+
+    private NuGetPackageDownloader CreateDownloader(HttpClient? httpClient = null)
+    {
+        var client = httpClient ?? new HttpClient();
+        var options = Options.Create(new NuGetDownloaderOptions());
+
+        return new NuGetPackageDownloader(
+            client,
+            NullLogger<NuGetPackageDownloader>.Instance,
+            options);
+    }
+
+    private static byte[] CreateMinimalNupkg()
+    {
+        // Create a minimal valid ZIP file (which is what a .nupkg is)
+        using var ms = new MemoryStream();
+        using (var archive = new System.IO.Compression.ZipArchive(ms, System.IO.Compression.ZipArchiveMode.Create, leaveOpen: true))
+        {
+            // Add a minimal .nuspec file
+            var nuspecEntry = archive.CreateEntry("test.nuspec");
+            using var writer = new StreamWriter(nuspecEntry.Open());
+            writer.Write("""
+                <?xml version="1.0"?>
+                <package xmlns="http://schemas.microsoft.com/packaging/2013/05/nuspec.xsd">
+                  <metadata>
+                    <id>TestPackage</id>
+                    <version>1.0.0</version>
+                    <authors>Test</authors>
+                    <description>Test package</description>
+                  </metadata>
+                </package>
+                """);
+        }
+
+        return ms.ToArray();
+    }
+}

src/Scanner/__Libraries/StellaOps.Scanner.VulnSurfaces/Builder/VulnSurfaceBuilder.cs

@@ -13,6 +13,7 @@ using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.Extensions.Logging;
 using StellaOps.Scanner.VulnSurfaces.CallGraph;
+using StellaOps.Scanner.VulnSurfaces.Diagnostics;
 using StellaOps.Scanner.VulnSurfaces.Download;
 using StellaOps.Scanner.VulnSurfaces.Fingerprint;
 using StellaOps.Scanner.VulnSurfaces.Models;
@@ -56,6 +57,12 @@ public sealed class VulnSurfaceBuilder : IVulnSurfaceBuilder
         ArgumentNullException.ThrowIfNull(request);
 
         var sw = Stopwatch.StartNew();
+        var tags = new KeyValuePair<string, object?>[]
+        {
+            new("ecosystem", request.Ecosystem.ToLowerInvariant())
+        };
+
+        VulnSurfaceMetrics.BuildRequests.Add(1, tags);
 
         _logger.LogInformation(
             "Building vulnerability surface for {CveId}: {Package} {VulnVersion} → {FixedVersion}",
@@ -87,6 +94,8 @@ public sealed class VulnSurfaceBuilder : IVulnSurfaceBuilder
             Directory.CreateDirectory(workDir);
 
             // 3. Download both versions
+            VulnSurfaceMetrics.DownloadAttempts.Add(2, tags); // Two versions
+
             var vulnDownload = await downloader.DownloadAsync(new PackageDownloadRequest
             {
                 PackageName = request.PackageName,
@@ -98,9 +107,14 @@ public sealed class VulnSurfaceBuilder : IVulnSurfaceBuilder
             if (!vulnDownload.Success)
             {
                 sw.Stop();
+                VulnSurfaceMetrics.DownloadFailures.Add(1, tags);
+                VulnSurfaceMetrics.BuildFailures.Add(1, new KeyValuePair<string, object?>[] { new("ecosystem", request.Ecosystem.ToLowerInvariant()), new("reason", "download_vuln") });
                 return VulnSurfaceBuildResult.Fail($"Failed to download vulnerable version: {vulnDownload.Error}", sw.Elapsed);
             }
 
+            VulnSurfaceMetrics.DownloadSuccesses.Add(1, tags);
+            VulnSurfaceMetrics.DownloadDurationSeconds.Record(vulnDownload.Duration.TotalSeconds, tags);
+
             var fixedDownload = await downloader.DownloadAsync(new PackageDownloadRequest
             {
                 PackageName = request.PackageName,
@@ -112,10 +126,16 @@ public sealed class VulnSurfaceBuilder : IVulnSurfaceBuilder
             if (!fixedDownload.Success)
             {
                 sw.Stop();
+                VulnSurfaceMetrics.DownloadFailures.Add(1, tags);
+                VulnSurfaceMetrics.BuildFailures.Add(1, new KeyValuePair<string, object?>[] { new("ecosystem", request.Ecosystem.ToLowerInvariant()), new("reason", "download_fixed") });
                 return VulnSurfaceBuildResult.Fail($"Failed to download fixed version: {fixedDownload.Error}", sw.Elapsed);
             }
 
+            VulnSurfaceMetrics.DownloadSuccesses.Add(1, tags);
+            VulnSurfaceMetrics.DownloadDurationSeconds.Record(fixedDownload.Duration.TotalSeconds, tags);
+
             // 4. Fingerprint both versions
+            var fpSw = Stopwatch.StartNew();
             var vulnFingerprints = await fingerprinter.FingerprintAsync(new FingerprintRequest
             {
                 PackagePath = vulnDownload.ExtractedPath!,
@@ -126,9 +146,15 @@ public sealed class VulnSurfaceBuilder : IVulnSurfaceBuilder
             if (!vulnFingerprints.Success)
             {
                 sw.Stop();
+                VulnSurfaceMetrics.BuildFailures.Add(1, new KeyValuePair<string, object?>[] { new("ecosystem", request.Ecosystem.ToLowerInvariant()), new("reason", "fingerprint_vuln") });
                 return VulnSurfaceBuildResult.Fail($"Failed to fingerprint vulnerable version: {vulnFingerprints.Error}", sw.Elapsed);
             }
 
+            VulnSurfaceMetrics.FingerprintDurationSeconds.Record(fpSw.Elapsed.TotalSeconds, tags);
+            VulnSurfaceMetrics.MethodsFingerprinted.Add(vulnFingerprints.Methods.Count, tags);
+            VulnSurfaceMetrics.MethodsPerPackage.Record(vulnFingerprints.Methods.Count, tags);
+
+            fpSw.Restart();
             var fixedFingerprints = await fingerprinter.FingerprintAsync(new FingerprintRequest
             {
                 PackagePath = fixedDownload.ExtractedPath!,
@@ -139,10 +165,16 @@ public sealed class VulnSurfaceBuilder : IVulnSurfaceBuilder
             if (!fixedFingerprints.Success)
             {
                 sw.Stop();
+                VulnSurfaceMetrics.BuildFailures.Add(1, new KeyValuePair<string, object?>[] { new("ecosystem", request.Ecosystem.ToLowerInvariant()), new("reason", "fingerprint_fixed") });
                 return VulnSurfaceBuildResult.Fail($"Failed to fingerprint fixed version: {fixedFingerprints.Error}", sw.Elapsed);
             }
 
+            VulnSurfaceMetrics.FingerprintDurationSeconds.Record(fpSw.Elapsed.TotalSeconds, tags);
+            VulnSurfaceMetrics.MethodsFingerprinted.Add(fixedFingerprints.Methods.Count, tags);
+            VulnSurfaceMetrics.MethodsPerPackage.Record(fixedFingerprints.Methods.Count, tags);
+
             // 5. Compute diff
+            var diffSw = Stopwatch.StartNew();
             var diff = await _diffEngine.DiffAsync(new MethodDiffRequest
             {
                 VulnFingerprints = vulnFingerprints,
@@ -152,9 +184,12 @@ public sealed class VulnSurfaceBuilder : IVulnSurfaceBuilder
             if (!diff.Success)
             {
                 sw.Stop();
+                VulnSurfaceMetrics.BuildFailures.Add(1, new KeyValuePair<string, object?>[] { new("ecosystem", request.Ecosystem.ToLowerInvariant()), new("reason", "diff") });
                 return VulnSurfaceBuildResult.Fail($"Failed to compute diff: {diff.Error}", sw.Elapsed);
             }
 
+            VulnSurfaceMetrics.DiffDurationSeconds.Record(diffSw.Elapsed.TotalSeconds, tags);
+
             // 6. Build sinks from diff
             var sinks = BuildSinks(diff);
 
@@ -209,6 +244,13 @@ public sealed class VulnSurfaceBuilder : IVulnSurfaceBuilder
 
             sw.Stop();
 
+            // Record success metrics
+            VulnSurfaceMetrics.BuildSuccesses.Add(1, tags);
+            VulnSurfaceMetrics.BuildDurationSeconds.Record(sw.Elapsed.TotalSeconds, tags);
+            VulnSurfaceMetrics.SinksPerSurface.Record(sinks.Count, tags);
+            VulnSurfaceMetrics.SinksIdentified.Add(sinks.Count, tags);
+            VulnSurfaceMetrics.IncrementEcosystemCount(request.Ecosystem);
+
             _logger.LogInformation(
                 "Built vulnerability surface for {CveId}: {SinkCount} sinks, {TriggerCount} triggers in {Duration}ms",
                 request.CveId, sinks.Count, triggerCount, sw.ElapsedMilliseconds);
@@ -218,6 +260,16 @@ public sealed class VulnSurfaceBuilder : IVulnSurfaceBuilder
         catch (Exception ex)
         {
             sw.Stop();
+
+            // Record failure metrics
+            var failTags = new KeyValuePair<string, object?>[]
+            {
+                new("ecosystem", request.Ecosystem.ToLowerInvariant()),
+                new("reason", "exception")
+            };
+            VulnSurfaceMetrics.BuildFailures.Add(1, failTags);
+            VulnSurfaceMetrics.BuildDurationSeconds.Record(sw.Elapsed.TotalSeconds, tags);
+
             _logger.LogError(ex, "Failed to build vulnerability surface for {CveId}", request.CveId);
             return VulnSurfaceBuildResult.Fail(ex.Message, sw.Elapsed);
         }

src/Scanner/__Libraries/StellaOps.Scanner.VulnSurfaces/Diagnostics/VulnSurfaceMetrics.cs

@@ -0,0 +1,233 @@
+// -----------------------------------------------------------------------------
+// VulnSurfaceMetrics.cs
+// Sprint: SPRINT_3700_0002_0001_vuln_surfaces_core
+// Task: SURF-019
+// Description: Metrics for vulnerability surface computation.
+// -----------------------------------------------------------------------------
+
+using System.Diagnostics.Metrics;
+
+namespace StellaOps.Scanner.VulnSurfaces.Diagnostics;
+
+/// <summary>
+/// Metrics for vulnerability surface computation and caching.
+/// </summary>
+public static class VulnSurfaceMetrics
+{
+    private static readonly Meter Meter = new("StellaOps.Scanner.VulnSurfaces", "1.0.0");
+
+    // ===== BUILD COUNTERS =====
+
+    /// <summary>
+    /// Total surface build requests by ecosystem.
+    /// </summary>
+    public static readonly Counter<long> BuildRequests = Meter.CreateCounter<long>(
+        "stellaops_vulnsurface_build_requests_total",
+        description: "Total vulnerability surface build requests");
+
+    /// <summary>
+    /// Successful surface builds by ecosystem.
+    /// </summary>
+    public static readonly Counter<long> BuildSuccesses = Meter.CreateCounter<long>(
+        "stellaops_vulnsurface_build_successes_total",
+        description: "Total successful vulnerability surface builds");
+
+    /// <summary>
+    /// Failed surface builds by ecosystem and reason.
+    /// </summary>
+    public static readonly Counter<long> BuildFailures = Meter.CreateCounter<long>(
+        "stellaops_vulnsurface_build_failures_total",
+        description: "Total failed vulnerability surface builds");
+
+    /// <summary>
+    /// Cache hits when surface already computed.
+    /// </summary>
+    public static readonly Counter<long> CacheHits = Meter.CreateCounter<long>(
+        "stellaops_vulnsurface_cache_hits_total",
+        description: "Total cache hits for pre-computed surfaces");
+
+    // ===== DOWNLOAD COUNTERS =====
+
+    /// <summary>
+    /// Package downloads attempted by ecosystem.
+    /// </summary>
+    public static readonly Counter<long> DownloadAttempts = Meter.CreateCounter<long>(
+        "stellaops_vulnsurface_downloads_attempted_total",
+        description: "Total package download attempts");
+
+    /// <summary>
+    /// Successful package downloads.
+    /// </summary>
+    public static readonly Counter<long> DownloadSuccesses = Meter.CreateCounter<long>(
+        "stellaops_vulnsurface_downloads_succeeded_total",
+        description: "Total successful package downloads");
+
+    /// <summary>
+    /// Failed package downloads.
+    /// </summary>
+    public static readonly Counter<long> DownloadFailures = Meter.CreateCounter<long>(
+        "stellaops_vulnsurface_downloads_failed_total",
+        description: "Total failed package downloads");
+
+    // ===== FINGERPRINT COUNTERS =====
+
+    /// <summary>
+    /// Methods fingerprinted by ecosystem.
+    /// </summary>
+    public static readonly Counter<long> MethodsFingerprinted = Meter.CreateCounter<long>(
+        "stellaops_vulnsurface_methods_fingerprinted_total",
+        description: "Total methods fingerprinted");
+
+    /// <summary>
+    /// Methods changed (sinks) identified.
+    /// </summary>
+    public static readonly Counter<long> SinksIdentified = Meter.CreateCounter<long>(
+        "stellaops_vulnsurface_sinks_identified_total",
+        description: "Total sink methods (changed methods) identified");
+
+    // ===== TIMING HISTOGRAMS =====
+
+    /// <summary>
+    /// End-to-end surface build duration.
+    /// </summary>
+    public static readonly Histogram<double> BuildDurationSeconds = Meter.CreateHistogram<double>(
+        "stellaops_vulnsurface_build_duration_seconds",
+        unit: "s",
+        description: "Duration of surface build operations",
+        advice: new InstrumentAdvice<double>
+        {
+            HistogramBucketBoundaries = [0.1, 0.5, 1.0, 2.5, 5.0, 10.0, 30.0, 60.0, 120.0]
+        });
+
+    /// <summary>
+    /// Package download duration.
+    /// </summary>
+    public static readonly Histogram<double> DownloadDurationSeconds = Meter.CreateHistogram<double>(
+        "stellaops_vulnsurface_download_duration_seconds",
+        unit: "s",
+        description: "Duration of package download operations",
+        advice: new InstrumentAdvice<double>
+        {
+            HistogramBucketBoundaries = [0.1, 0.5, 1.0, 2.5, 5.0, 10.0, 30.0]
+        });
+
+    /// <summary>
+    /// Fingerprinting duration per package.
+    /// </summary>
+    public static readonly Histogram<double> FingerprintDurationSeconds = Meter.CreateHistogram<double>(
+        "stellaops_vulnsurface_fingerprint_duration_seconds",
+        unit: "s",
+        description: "Duration of fingerprinting operations",
+        advice: new InstrumentAdvice<double>
+        {
+            HistogramBucketBoundaries = [0.05, 0.1, 0.25, 0.5, 1.0, 2.5, 5.0, 10.0]
+        });
+
+    /// <summary>
+    /// Diff computation duration.
+    /// </summary>
+    public static readonly Histogram<double> DiffDurationSeconds = Meter.CreateHistogram<double>(
+        "stellaops_vulnsurface_diff_duration_seconds",
+        unit: "s",
+        description: "Duration of diff computation",
+        advice: new InstrumentAdvice<double>
+        {
+            HistogramBucketBoundaries = [0.001, 0.01, 0.05, 0.1, 0.25, 0.5, 1.0]
+        });
+
+    // ===== SIZE HISTOGRAMS =====
+
+    /// <summary>
+    /// Number of methods per package version.
+    /// </summary>
+    public static readonly Histogram<int> MethodsPerPackage = Meter.CreateHistogram<int>(
+        "stellaops_vulnsurface_methods_per_package",
+        description: "Number of methods per analyzed package version",
+        advice: new InstrumentAdvice<int>
+        {
+            HistogramBucketBoundaries = [10, 50, 100, 250, 500, 1000, 2500, 5000, 10000]
+        });
+
+    /// <summary>
+    /// Number of sinks per surface.
+    /// </summary>
+    public static readonly Histogram<int> SinksPerSurface = Meter.CreateHistogram<int>(
+        "stellaops_vulnsurface_sinks_per_surface",
+        description: "Number of sink methods per vulnerability surface",
+        advice: new InstrumentAdvice<int>
+        {
+            HistogramBucketBoundaries = [1, 2, 5, 10, 25, 50, 100, 250]
+        });
+
+    // ===== ECOSYSTEM DISTRIBUTION =====
+
+    private static int _nugetSurfaces;
+    private static int _npmSurfaces;
+    private static int _mavenSurfaces;
+    private static int _pypiSurfaces;
+
+    /// <summary>
+    /// Current count of NuGet surfaces.
+    /// </summary>
+    public static readonly ObservableGauge<int> NuGetSurfaceCount = Meter.CreateObservableGauge(
+        "stellaops_vulnsurface_nuget_count",
+        () => _nugetSurfaces,
+        description: "Current count of NuGet vulnerability surfaces");
+
+    /// <summary>
+    /// Current count of npm surfaces.
+    /// </summary>
+    public static readonly ObservableGauge<int> NpmSurfaceCount = Meter.CreateObservableGauge(
+        "stellaops_vulnsurface_npm_count",
+        () => _npmSurfaces,
+        description: "Current count of npm vulnerability surfaces");
+
+    /// <summary>
+    /// Current count of Maven surfaces.
+    /// </summary>
+    public static readonly ObservableGauge<int> MavenSurfaceCount = Meter.CreateObservableGauge(
+        "stellaops_vulnsurface_maven_count",
+        () => _mavenSurfaces,
+        description: "Current count of Maven vulnerability surfaces");
+
+    /// <summary>
+    /// Current count of PyPI surfaces.
+    /// </summary>
+    public static readonly ObservableGauge<int> PyPISurfaceCount = Meter.CreateObservableGauge(
+        "stellaops_vulnsurface_pypi_count",
+        () => _pypiSurfaces,
+        description: "Current count of PyPI vulnerability surfaces");
+
+    /// <summary>
+    /// Updates the ecosystem surface counts.
+    /// </summary>
+    public static void SetEcosystemCounts(int nuget, int npm, int maven, int pypi)
+    {
+        Interlocked.Exchange(ref _nugetSurfaces, nuget);
+        Interlocked.Exchange(ref _npmSurfaces, npm);
+        Interlocked.Exchange(ref _mavenSurfaces, maven);
+        Interlocked.Exchange(ref _pypiSurfaces, pypi);
+    }
+
+    /// <summary>
+    /// Increments the surface count for an ecosystem.
+    /// </summary>
+    public static void IncrementEcosystemCount(string ecosystem)
+    {
+        switch (ecosystem.ToLowerInvariant())
+        {
+            case "nuget":
+                Interlocked.Increment(ref _nugetSurfaces);
+                break;
+            case "npm":
+                Interlocked.Increment(ref _npmSurfaces);
+                break;
+            case "maven":
+                Interlocked.Increment(ref _mavenSurfaces);
+                break;
+            case "pypi":
+                Interlocked.Increment(ref _pypiSurfaces);
+                break;
+        }
+    }
+}

src/Scanner/__Libraries/StellaOps.Scanner.VulnSurfaces/Models/VulnSurface.cs

@@ -124,6 +124,12 @@ public sealed record VulnSurfaceSink
     [JsonPropertyName("method_name")]
     public required string MethodName { get; init; }
 
+    /// <summary>
+    /// Namespace/package.
+    /// </summary>
+    [JsonPropertyName("namespace")]
+    public string? Namespace { get; init; }
+
     /// <summary>
     /// Method signature.
     /// </summary>
@@ -153,6 +159,42 @@ public sealed record VulnSurfaceSink
     /// </summary>
     [JsonPropertyName("is_direct_exploit")]
     public bool IsDirectExploit { get; init; }
+
+    /// <summary>
+    /// Whether the method is public.
+    /// </summary>
+    [JsonPropertyName("is_public")]
+    public bool IsPublic { get; init; }
+
+    /// <summary>
+    /// Number of parameters.
+    /// </summary>
+    [JsonPropertyName("parameter_count")]
+    public int? ParameterCount { get; init; }
+
+    /// <summary>
+    /// Return type.
+    /// </summary>
+    [JsonPropertyName("return_type")]
+    public string? ReturnType { get; init; }
+
+    /// <summary>
+    /// Source file path (if available from debug symbols).
+    /// </summary>
+    [JsonPropertyName("source_file")]
+    public string? SourceFile { get; init; }
+
+    /// <summary>
+    /// Start line number.
+    /// </summary>
+    [JsonPropertyName("start_line")]
+    public int? StartLine { get; init; }
+
+    /// <summary>
+    /// End line number.
+    /// </summary>
+    [JsonPropertyName("end_line")]
+    public int? EndLine { get; init; }
 }
 
 /// <summary>

src/Scanner/__Libraries/StellaOps.Scanner.VulnSurfaces/StellaOps.Scanner.VulnSurfaces.csproj

@@ -14,6 +14,7 @@
     <PackageReference Include="Microsoft.Extensions.Logging.Abstractions" Version="10.0.0" />
     <PackageReference Include="Microsoft.Extensions.Options" Version="10.0.0" />
     <PackageReference Include="Mono.Cecil" Version="0.11.6" />
+    <PackageReference Include="Npgsql" Version="9.0.3" />
   </ItemGroup>
 
   <ItemGroup>

src/Scanner/__Libraries/StellaOps.Scanner.VulnSurfaces/Storage/IVulnSurfaceRepository.cs

@@ -0,0 +1,99 @@
+// -----------------------------------------------------------------------------
+// IVulnSurfaceRepository.cs
+// Sprint: SPRINT_3700_0002_0001_vuln_surfaces_core
+// Task: SURF-016
+// Description: Repository interface for vulnerability surfaces.
+// -----------------------------------------------------------------------------
+
+using StellaOps.Scanner.VulnSurfaces.Models;
+
+namespace StellaOps.Scanner.VulnSurfaces.Storage;
+
+/// <summary>
+/// Repository interface for vulnerability surface storage.
+/// </summary>
+public interface IVulnSurfaceRepository
+{
+    /// <summary>
+    /// Creates a new vulnerability surface.
+    /// </summary>
+    Task<Guid> CreateSurfaceAsync(
+        Guid tenantId,
+        string cveId,
+        string ecosystem,
+        string packageName,
+        string vulnVersion,
+        string? fixedVersion,
+        string fingerprintMethod,
+        int totalMethodsVuln,
+        int totalMethodsFixed,
+        int changedMethodCount,
+        int? computationDurationMs,
+        string? attestationDigest,
+        CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Adds a sink method to a vulnerability surface.
+    /// </summary>
+    Task<Guid> AddSinkAsync(
+        Guid surfaceId,
+        string methodKey,
+        string methodName,
+        string declaringType,
+        string changeType,
+        string? vulnHash,
+        string? fixedHash,
+        CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Adds a trigger to a surface.
+    /// </summary>
+    Task<Guid> AddTriggerAsync(
+        Guid surfaceId,
+        string triggerMethodKey,
+        string sinkMethodKey,
+        int depth,
+        double confidence,
+        CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Gets a vulnerability surface by CVE and package.
+    /// </summary>
+    Task<VulnSurface?> GetByCveAndPackageAsync(
+        Guid tenantId,
+        string cveId,
+        string ecosystem,
+        string packageName,
+        string vulnVersion,
+        CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Gets sinks for a vulnerability surface.
+    /// </summary>
+    Task<IReadOnlyList<VulnSurfaceSink>> GetSinksAsync(
+        Guid surfaceId,
+        CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Gets triggers for a vulnerability surface.
+    /// </summary>
+    Task<IReadOnlyList<VulnSurfaceTrigger>> GetTriggersAsync(
+        Guid surfaceId,
+        CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Gets all surfaces for a CVE.
+    /// </summary>
+    Task<IReadOnlyList<VulnSurface>> GetSurfacesByCveAsync(
+        Guid tenantId,
+        string cveId,
+        CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Deletes a vulnerability surface and all related data.
+    /// </summary>
+    Task<bool> DeleteSurfaceAsync(
+        Guid surfaceId,
+        CancellationToken cancellationToken = default);
+}
+

src/Scanner/__Libraries/StellaOps.Scanner.VulnSurfaces/Storage/IVulnSurfaceRepository.cs.bak

@@ -0,0 +1,100 @@
+// -----------------------------------------------------------------------------
+// IVulnSurfaceRepository.cs
+// Sprint: SPRINT_3700_0002_0001_vuln_surfaces_core
+// Task: SURF-016
+// Description: Repository interface for vulnerability surfaces.
+// -----------------------------------------------------------------------------
+
+using StellaOps.Scanner.VulnSurfaces.Models;
+
+namespace StellaOps.Scanner.VulnSurfaces.Storage;
+
+/// <summary>
+/// Repository interface for vulnerability surface storage.
+/// </summary>
+public interface IVulnSurfaceRepository
+{
+    /// <summary>
+    /// Creates a new vulnerability surface.
+    /// </summary>
+    Task<Guid> CreateSurfaceAsync(
+        Guid tenantId,
+        string cveId,
+        string ecosystem,
+        string packageName,
+        string vulnVersion,
+        string? fixedVersion,
+        string fingerprintMethod,
+        int totalMethodsVuln,
+        int totalMethodsFixed,
+        int changedMethodCount,
+        int? computationDurationMs,
+        string? attestationDigest,
+        CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Adds a sink method to a vulnerability surface.
+    /// </summary>
+    Task<Guid> AddSinkAsync(
+        Guid surfaceId,
+        string methodKey,
+        string methodName,
+        string declaringType,
+        string changeType,
+        string? vulnHash,
+        string? fixedHash,
+        CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Adds a trigger to a surface.
+    /// </summary>
+    Task<Guid> AddTriggerAsync(
+        Guid surfaceId,
+        string triggerMethodKey,
+        string sinkMethodKey,
+        int depth,
+        double confidence,
+        CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Gets a vulnerability surface by CVE and package.
+    /// </summary>
+    Task<VulnSurface?> GetByCveAndPackageAsync(
+        Guid tenantId,
+        string cveId,
+        string ecosystem,
+        string packageName,
+        string vulnVersion,
+        CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Gets sinks for a vulnerability surface.
+    /// </summary>
+    Task<IReadOnlyList<VulnSurfaceSink>> GetSinksAsync(
+        Guid surfaceId,
+        CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Gets triggers for a vulnerability surface.
+    /// </summary>
+    Task<IReadOnlyList<VulnSurfaceTrigger>> GetTriggersAsync(
+        Guid surfaceId,
+        CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Gets all surfaces for a CVE.
+    /// </summary>
+    Task<IReadOnlyList<VulnSurface>> GetSurfacesByCveAsync(
+        Guid tenantId,
+        string cveId,
+        CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Deletes a vulnerability surface and all related data.
+    /// </summary>
+    Task<bool> DeleteSurfaceAsync(
+        Guid surfaceId,
+        CancellationToken cancellationToken = default);
+}
+
+

src/Scanner/__Libraries/StellaOps.Scanner.VulnSurfaces/Storage/PostgresVulnSurfaceRepository.cs

@@ -0,0 +1,400 @@
+// -----------------------------------------------------------------------------
+// PostgresVulnSurfaceRepository.cs
+// Sprint: SPRINT_3700_0002_0001_vuln_surfaces_core
+// Task: SURF-016
+// Description: PostgreSQL implementation of vulnerability surface repository.
+// -----------------------------------------------------------------------------
+
+using Microsoft.Extensions.Logging;
+using Npgsql;
+using StellaOps.Scanner.VulnSurfaces.Models;
+
+namespace StellaOps.Scanner.VulnSurfaces.Storage;
+
+/// <summary>
+/// PostgreSQL implementation of vulnerability surface repository.
+/// </summary>
+public sealed class PostgresVulnSurfaceRepository : IVulnSurfaceRepository
+{
+    private readonly NpgsqlDataSource _dataSource;
+    private readonly ILogger<PostgresVulnSurfaceRepository> _logger;
+    private readonly int _commandTimeoutSeconds;
+
+    public PostgresVulnSurfaceRepository(
+        NpgsqlDataSource dataSource,
+        ILogger<PostgresVulnSurfaceRepository> logger,
+        int commandTimeoutSeconds = 30)
+    {
+        _dataSource = dataSource ?? throw new ArgumentNullException(nameof(dataSource));
+        _logger = logger ?? throw new ArgumentNullException(nameof(logger));
+        _commandTimeoutSeconds = commandTimeoutSeconds;
+    }
+
+    public async Task<Guid> CreateSurfaceAsync(
+        Guid tenantId,
+        string cveId,
+        string ecosystem,
+        string packageName,
+        string vulnVersion,
+        string? fixedVersion,
+        string fingerprintMethod,
+        int totalMethodsVuln,
+        int totalMethodsFixed,
+        int changedMethodCount,
+        int? computationDurationMs,
+        string? attestationDigest,
+        CancellationToken cancellationToken = default)
+    {
+        var id = Guid.NewGuid();
+
+        const string sql = """
+            INSERT INTO scanner.vuln_surfaces (
+                id, tenant_id, cve_id, package_ecosystem, package_name,
+                vuln_version, fixed_version, fingerprint_method,
+                total_methods_vuln, total_methods_fixed, changed_method_count,
+                computation_duration_ms, attestation_digest
+            ) VALUES (
+                @id, @tenant_id, @cve_id, @ecosystem, @package_name,
+                @vuln_version, @fixed_version, @fingerprint_method,
+                @total_methods_vuln, @total_methods_fixed, @changed_method_count,
+                @computation_duration_ms, @attestation_digest
+            )
+            ON CONFLICT (tenant_id, cve_id, package_ecosystem, package_name, vuln_version)
+            DO UPDATE SET
+                fixed_version = EXCLUDED.fixed_version,
+                fingerprint_method = EXCLUDED.fingerprint_method,
+                total_methods_vuln = EXCLUDED.total_methods_vuln,
+                total_methods_fixed = EXCLUDED.total_methods_fixed,
+                changed_method_count = EXCLUDED.changed_method_count,
+                computation_duration_ms = EXCLUDED.computation_duration_ms,
+                attestation_digest = EXCLUDED.attestation_digest,
+                computed_at = now()
+            RETURNING id
+            """;
+
+        await using var connection = await _dataSource.OpenConnectionAsync(cancellationToken);
+        await SetTenantContextAsync(connection, tenantId, cancellationToken);
+
+        await using var command = new NpgsqlCommand(sql, connection);
+        command.CommandTimeout = _commandTimeoutSeconds;
+
+        command.Parameters.AddWithValue("id", id);
+        command.Parameters.AddWithValue("tenant_id", tenantId);
+        command.Parameters.AddWithValue("cve_id", cveId);
+        command.Parameters.AddWithValue("ecosystem", ecosystem);
+        command.Parameters.AddWithValue("package_name", packageName);
+        command.Parameters.AddWithValue("vuln_version", vulnVersion);
+        command.Parameters.AddWithValue("fixed_version", (object?)fixedVersion ?? DBNull.Value);
+        command.Parameters.AddWithValue("fingerprint_method", fingerprintMethod);
+        command.Parameters.AddWithValue("total_methods_vuln", totalMethodsVuln);
+        command.Parameters.AddWithValue("total_methods_fixed", totalMethodsFixed);
+        command.Parameters.AddWithValue("changed_method_count", changedMethodCount);
+        command.Parameters.AddWithValue("computation_duration_ms", (object?)computationDurationMs ?? DBNull.Value);
+        command.Parameters.AddWithValue("attestation_digest", (object?)attestationDigest ?? DBNull.Value);
+
+        var result = await command.ExecuteScalarAsync(cancellationToken);
+        return (Guid)result!;
+    }
+
+    public async Task<Guid> AddSinkAsync(
+        Guid surfaceId,
+        string methodKey,
+        string methodName,
+        string declaringType,
+        string changeType,
+        string? vulnHash,
+        string? fixedHash,
+        CancellationToken cancellationToken = default)
+    {
+        var id = Guid.NewGuid();
+
+        const string sql = """
+            INSERT INTO scanner.vuln_surface_sinks (
+                id, surface_id, method_key, method_name, declaring_type,
+                change_type, vuln_fingerprint, fixed_fingerprint
+            ) VALUES (
+                @id, @surface_id, @method_key, @method_name, @declaring_type,
+                @change_type, @vuln_hash, @fixed_hash
+            )
+            ON CONFLICT (surface_id, method_key) DO UPDATE SET
+                change_type = EXCLUDED.change_type,
+                vuln_fingerprint = EXCLUDED.vuln_fingerprint,
+                fixed_fingerprint = EXCLUDED.fixed_fingerprint
+            RETURNING id
+            """;
+
+        await using var connection = await _dataSource.OpenConnectionAsync(cancellationToken);
+        await using var command = new NpgsqlCommand(sql, connection);
+        command.CommandTimeout = _commandTimeoutSeconds;
+
+        command.Parameters.AddWithValue("id", id);
+        command.Parameters.AddWithValue("surface_id", surfaceId);
+        command.Parameters.AddWithValue("method_key", methodKey);
+        command.Parameters.AddWithValue("method_name", methodName);
+        command.Parameters.AddWithValue("declaring_type", declaringType);
+        command.Parameters.AddWithValue("change_type", changeType);
+        command.Parameters.AddWithValue("vuln_hash", (object?)vulnHash ?? DBNull.Value);
+        command.Parameters.AddWithValue("fixed_hash", (object?)fixedHash ?? DBNull.Value);
+
+        var result = await command.ExecuteScalarAsync(cancellationToken);
+        return (Guid)result!;
+    }
+
+    public async Task<Guid> AddTriggerAsync(
+        Guid surfaceId,
+        string triggerMethodKey,
+        string sinkMethodKey,
+        int depth,
+        double confidence,
+        CancellationToken cancellationToken = default)
+    {
+        var id = Guid.NewGuid();
+
+        const string sql = """
+            INSERT INTO scanner.vuln_surface_triggers (
+                id, sink_id, scan_id, caller_node_id, caller_method_key,
+                reachability_bucket, path_length, confidence, call_type, is_conditional
+            ) VALUES (
+                @id, 
+                (SELECT id FROM scanner.vuln_surface_sinks WHERE surface_id = @surface_id AND method_key = @sink_method_key LIMIT 1),
+                @surface_id::uuid,
+                @trigger_method_key,
+                @trigger_method_key,
+                'direct',
+                @depth,
+                @confidence,
+                'direct',
+                false
+            )
+            RETURNING id
+            """;
+
+        await using var connection = await _dataSource.OpenConnectionAsync(cancellationToken);
+        await using var command = new NpgsqlCommand(sql, connection);
+        command.CommandTimeout = _commandTimeoutSeconds;
+
+        command.Parameters.AddWithValue("id", id);
+        command.Parameters.AddWithValue("surface_id", surfaceId);
+        command.Parameters.AddWithValue("trigger_method_key", triggerMethodKey);
+        command.Parameters.AddWithValue("sink_method_key", sinkMethodKey);
+        command.Parameters.AddWithValue("depth", depth);
+        command.Parameters.AddWithValue("confidence", (float)confidence);
+
+        var result = await command.ExecuteScalarAsync(cancellationToken);
+        return result is Guid g ? g : Guid.Empty;
+    }
+
+    public async Task<VulnSurface?> GetByCveAndPackageAsync(
+        Guid tenantId,
+        string cveId,
+        string ecosystem,
+        string packageName,
+        string vulnVersion,
+        CancellationToken cancellationToken = default)
+    {
+        const string sql = """
+            SELECT id, tenant_id, cve_id, package_ecosystem, package_name,
+                   vuln_version, fixed_version, fingerprint_method,
+                   total_methods_vuln, total_methods_fixed, changed_method_count,
+                   computation_duration_ms, attestation_digest, computed_at
+            FROM scanner.vuln_surfaces
+            WHERE tenant_id = @tenant_id
+              AND cve_id = @cve_id
+              AND package_ecosystem = @ecosystem
+              AND package_name = @package_name
+              AND vuln_version = @vuln_version
+            """;
+
+        await using var connection = await _dataSource.OpenConnectionAsync(cancellationToken);
+        await SetTenantContextAsync(connection, tenantId, cancellationToken);
+
+        await using var command = new NpgsqlCommand(sql, connection);
+        command.CommandTimeout = _commandTimeoutSeconds;
+
+        command.Parameters.AddWithValue("tenant_id", tenantId);
+        command.Parameters.AddWithValue("cve_id", cveId);
+        command.Parameters.AddWithValue("ecosystem", ecosystem);
+        command.Parameters.AddWithValue("package_name", packageName);
+        command.Parameters.AddWithValue("vuln_version", vulnVersion);
+
+        await using var reader = await command.ExecuteReaderAsync(cancellationToken);
+        if (!await reader.ReadAsync(cancellationToken))
+        {
+            return null;
+        }
+
+        return MapToVulnSurface(reader);
+    }
+
+    public async Task<IReadOnlyList<VulnSurfaceSink>> GetSinksAsync(
+        Guid surfaceId,
+        CancellationToken cancellationToken = default)
+    {
+        const string sql = """
+            SELECT id, surface_id, method_key, method_name, declaring_type,
+                   change_type, vuln_fingerprint, fixed_fingerprint
+            FROM scanner.vuln_surface_sinks
+            WHERE surface_id = @surface_id
+            ORDER BY declaring_type, method_name
+            """;
+
+        await using var connection = await _dataSource.OpenConnectionAsync(cancellationToken);
+        await using var command = new NpgsqlCommand(sql, connection);
+        command.CommandTimeout = _commandTimeoutSeconds;
+
+        command.Parameters.AddWithValue("surface_id", surfaceId);
+
+        var sinks = new List<VulnSurfaceSink>();
+        await using var reader = await command.ExecuteReaderAsync(cancellationToken);
+        while (await reader.ReadAsync(cancellationToken))
+        {
+            sinks.Add(MapToSink(reader));
+        }
+
+        return sinks;
+    }
+
+    public async Task<IReadOnlyList<VulnSurfaceTrigger>> GetTriggersAsync(
+        Guid surfaceId,
+        CancellationToken cancellationToken = default)
+    {
+        const string sql = """
+            SELECT vst.id, vss.surface_id, vst.caller_method_key, vss.method_key,
+                   vst.path_length, vst.confidence
+            FROM scanner.vuln_surface_triggers vst
+            JOIN scanner.vuln_surface_sinks vss ON vst.sink_id = vss.id
+            WHERE vss.surface_id = @surface_id
+            ORDER BY vst.path_length
+            """;
+
+        await using var connection = await _dataSource.OpenConnectionAsync(cancellationToken);
+        await using var command = new NpgsqlCommand(sql, connection);
+        command.CommandTimeout = _commandTimeoutSeconds;
+
+        command.Parameters.AddWithValue("surface_id", surfaceId);
+
+        var triggers = new List<VulnSurfaceTrigger>();
+        await using var reader = await command.ExecuteReaderAsync(cancellationToken);
+        while (await reader.ReadAsync(cancellationToken))
+        {
+            triggers.Add(MapToTrigger(reader));
+        }
+
+        return triggers;
+    }
+
+    public async Task<IReadOnlyList<VulnSurface>> GetSurfacesByCveAsync(
+        Guid tenantId,
+        string cveId,
+        CancellationToken cancellationToken = default)
+    {
+        const string sql = """
+            SELECT id, tenant_id, cve_id, package_ecosystem, package_name,
+                   vuln_version, fixed_version, fingerprint_method,
+                   total_methods_vuln, total_methods_fixed, changed_method_count,
+                   computation_duration_ms, attestation_digest, computed_at
+            FROM scanner.vuln_surfaces
+            WHERE tenant_id = @tenant_id AND cve_id = @cve_id
+            ORDER BY package_ecosystem, package_name, vuln_version
+            """;
+
+        await using var connection = await _dataSource.OpenConnectionAsync(cancellationToken);
+        await SetTenantContextAsync(connection, tenantId, cancellationToken);
+
+        await using var command = new NpgsqlCommand(sql, connection);
+        command.CommandTimeout = _commandTimeoutSeconds;
+
+        command.Parameters.AddWithValue("tenant_id", tenantId);
+        command.Parameters.AddWithValue("cve_id", cveId);
+
+        var surfaces = new List<VulnSurface>();
+        await using var reader = await command.ExecuteReaderAsync(cancellationToken);
+        while (await reader.ReadAsync(cancellationToken))
+        {
+            surfaces.Add(MapToVulnSurface(reader));
+        }
+
+        return surfaces;
+    }
+
+    public async Task<bool> DeleteSurfaceAsync(
+        Guid surfaceId,
+        CancellationToken cancellationToken = default)
+    {
+        const string sql = """
+            DELETE FROM scanner.vuln_surfaces WHERE id = @id
+            """;
+
+        await using var connection = await _dataSource.OpenConnectionAsync(cancellationToken);
+        await using var command = new NpgsqlCommand(sql, connection);
+        command.CommandTimeout = _commandTimeoutSeconds;
+
+        command.Parameters.AddWithValue("id", surfaceId);
+
+        var rows = await command.ExecuteNonQueryAsync(cancellationToken);
+        return rows > 0;
+    }
+
+    private static async Task SetTenantContextAsync(
+        NpgsqlConnection connection,
+        Guid tenantId,
+        CancellationToken cancellationToken)
+    {
+        await using var command = new NpgsqlCommand(
+            $"SET LOCAL app.tenant_id = '{tenantId}'",
+            connection);
+        await command.ExecuteNonQueryAsync(cancellationToken);
+    }
+
+    private static VulnSurface MapToVulnSurface(NpgsqlDataReader reader)
+    {
+        return new VulnSurface
+        {
+            SurfaceId = reader.GetGuid(0).GetHashCode(),
+            CveId = reader.GetString(2),
+            PackageId = $"pkg:{reader.GetString(3)}/{reader.GetString(4)}@{reader.GetString(5)}",
+            Ecosystem = reader.GetString(3),
+            VulnVersion = reader.GetString(5),
+            FixedVersion = reader.IsDBNull(6) ? string.Empty : reader.GetString(6),
+            Status = VulnSurfaceStatus.Computed,
+            Confidence = 1.0,
+            ComputedAt = reader.GetDateTime(13)
+        };
+    }
+
+    private static VulnSurfaceSink MapToSink(NpgsqlDataReader reader)
+    {
+        return new VulnSurfaceSink
+        {
+            SinkId = reader.GetGuid(0).GetHashCode(),
+            SurfaceId = reader.GetGuid(1).GetHashCode(),
+            MethodKey = reader.GetString(2),
+            MethodName = reader.GetString(3),
+            DeclaringType = reader.GetString(4),
+            ChangeType = ParseChangeType(reader.GetString(5)),
+            VulnHash = reader.IsDBNull(6) ? null : reader.GetString(6),
+            FixedHash = reader.IsDBNull(7) ? null : reader.GetString(7)
+        };
+    }
+
+    private static VulnSurfaceTrigger MapToTrigger(NpgsqlDataReader reader)
+    {
+        return new VulnSurfaceTrigger
+        {
+            SurfaceId = reader.GetGuid(1).GetHashCode(),
+            TriggerMethodKey = reader.GetString(2),
+            SinkMethodKey = reader.GetString(3),
+            Depth = reader.IsDBNull(4) ? 0 : reader.GetInt32(4),
+            Confidence = reader.IsDBNull(5) ? 1.0 : reader.GetFloat(5)
+        };
+    }
+
+    private static MethodChangeType ParseChangeType(string changeType) => changeType switch
+    {
+        "added" => MethodChangeType.Added,
+        "removed" => MethodChangeType.Removed,
+        "modified" => MethodChangeType.Modified,
+        "signaturechanged" => MethodChangeType.SignatureChanged,
+        _ => MethodChangeType.Modified
+    };
+}

src/Scanner/__Tests/StellaOps.Scanner.Reachability.Tests/AttestingRichGraphWriterTests.cs

@@ -0,0 +1,304 @@
+// -----------------------------------------------------------------------------
+// AttestingRichGraphWriterTests.cs
+// Sprint: SPRINT_3620_0001_0001_reachability_witness_dsse
+// Description: Tests for AttestingRichGraphWriter integration.
+// -----------------------------------------------------------------------------
+
+using Microsoft.Extensions.Logging.Abstractions;
+using Microsoft.Extensions.Options;
+using StellaOps.Cryptography;
+using StellaOps.Scanner.Reachability.Attestation;
+using Xunit;
+
+namespace StellaOps.Scanner.Reachability.Tests;
+
+public class AttestingRichGraphWriterTests : IAsyncLifetime
+{
+    private DirectoryInfo _tempDir = null!;
+
+    public Task InitializeAsync()
+    {
+        _tempDir = Directory.CreateTempSubdirectory("attesting-writer-test-");
+        return Task.CompletedTask;
+    }
+
+    public Task DisposeAsync()
+    {
+        try
+        {
+            if (_tempDir.Exists)
+            {
+                _tempDir.Delete(recursive: true);
+            }
+        }
+        catch
+        {
+            // Ignore cleanup errors
+        }
+        return Task.CompletedTask;
+    }
+
+    [Fact]
+    public async Task WriteWithAttestationAsync_WhenEnabled_ProducesAttestationFile()
+    {
+        // Arrange
+        var cryptoHash = new TestCryptoHash();
+        var graphWriter = new RichGraphWriter(cryptoHash);
+        var witnessOptions = Options.Create(new ReachabilityWitnessOptions
+        {
+            Enabled = true,
+            StoreInCas = false,
+            PublishToRekor = false
+        });
+        var witnessPublisher = new ReachabilityWitnessPublisher(
+            witnessOptions,
+            cryptoHash,
+            NullLogger<ReachabilityWitnessPublisher>.Instance);
+
+        var writer = new AttestingRichGraphWriter(
+            graphWriter,
+            witnessPublisher,
+            witnessOptions,
+            NullLogger<AttestingRichGraphWriter>.Instance);
+
+        var graph = CreateTestGraph();
+
+        // Act
+        var result = await writer.WriteWithAttestationAsync(
+            graph,
+            _tempDir.FullName,
+            "test-analysis",
+            "sha256:abc123");
+
+        // Assert
+        Assert.NotNull(result);
+        Assert.True(File.Exists(result.GraphPath));
+        Assert.True(File.Exists(result.MetaPath));
+        Assert.NotNull(result.AttestationPath);
+        Assert.True(File.Exists(result.AttestationPath));
+        Assert.NotNull(result.WitnessResult);
+        Assert.NotEmpty(result.WitnessResult.StatementHash);
+    }
+
+    [Fact]
+    public async Task WriteWithAttestationAsync_WhenDisabled_NoAttestationFile()
+    {
+        // Arrange
+        var cryptoHash = new TestCryptoHash();
+        var graphWriter = new RichGraphWriter(cryptoHash);
+        var witnessOptions = Options.Create(new ReachabilityWitnessOptions
+        {
+            Enabled = false
+        });
+        var witnessPublisher = new ReachabilityWitnessPublisher(
+            witnessOptions,
+            cryptoHash,
+            NullLogger<ReachabilityWitnessPublisher>.Instance);
+
+        var writer = new AttestingRichGraphWriter(
+            graphWriter,
+            witnessPublisher,
+            witnessOptions,
+            NullLogger<AttestingRichGraphWriter>.Instance);
+
+        var graph = CreateTestGraph();
+
+        // Act
+        var result = await writer.WriteWithAttestationAsync(
+            graph,
+            _tempDir.FullName,
+            "test-analysis",
+            "sha256:abc123");
+
+        // Assert
+        Assert.NotNull(result);
+        Assert.True(File.Exists(result.GraphPath));
+        Assert.True(File.Exists(result.MetaPath));
+        Assert.Null(result.AttestationPath);
+        Assert.Null(result.WitnessResult);
+    }
+
+    [Fact]
+    public async Task WriteWithAttestationAsync_AttestationContainsValidDsse()
+    {
+        // Arrange
+        var cryptoHash = new TestCryptoHash();
+        var graphWriter = new RichGraphWriter(cryptoHash);
+        var witnessOptions = Options.Create(new ReachabilityWitnessOptions
+        {
+            Enabled = true,
+            StoreInCas = false,
+            PublishToRekor = false
+        });
+        var witnessPublisher = new ReachabilityWitnessPublisher(
+            witnessOptions,
+            cryptoHash,
+            NullLogger<ReachabilityWitnessPublisher>.Instance);
+
+        var writer = new AttestingRichGraphWriter(
+            graphWriter,
+            witnessPublisher,
+            witnessOptions,
+            NullLogger<AttestingRichGraphWriter>.Instance);
+
+        var graph = CreateTestGraph();
+
+        // Act
+        var result = await writer.WriteWithAttestationAsync(
+            graph,
+            _tempDir.FullName,
+            "test-analysis",
+            "sha256:abc123");
+
+        // Assert
+        Assert.NotNull(result.AttestationPath);
+        var dsseJson = await File.ReadAllTextAsync(result.AttestationPath);
+        Assert.Contains("payloadType", dsseJson);
+        // Note: + may be encoded as \u002B in JSON
+        Assert.True(dsseJson.Contains("application/vnd.in-toto+json") || dsseJson.Contains("application/vnd.in-toto\\u002Bjson"));
+        Assert.Contains("payload", dsseJson);
+    }
+
+    [Fact]
+    public async Task WriteWithAttestationAsync_GraphHashIsDeterministic()
+    {
+        // Arrange
+        var cryptoHash = new TestCryptoHash();
+        var graphWriter = new RichGraphWriter(cryptoHash);
+        var witnessOptions = Options.Create(new ReachabilityWitnessOptions
+        {
+            Enabled = true,
+            StoreInCas = false,
+            PublishToRekor = false
+        });
+        var witnessPublisher = new ReachabilityWitnessPublisher(
+            witnessOptions,
+            cryptoHash,
+            NullLogger<ReachabilityWitnessPublisher>.Instance);
+
+        var writer = new AttestingRichGraphWriter(
+            graphWriter,
+            witnessPublisher,
+            witnessOptions,
+            NullLogger<AttestingRichGraphWriter>.Instance);
+
+        var graph = CreateTestGraph();
+
+        // Act - write twice with same input
+        var result1 = await writer.WriteWithAttestationAsync(
+            graph,
+            _tempDir.FullName,
+            "analysis-1",
+            "sha256:abc123");
+
+        var result2 = await writer.WriteWithAttestationAsync(
+            graph,
+            _tempDir.FullName,
+            "analysis-2",
+            "sha256:abc123");
+
+        // Assert - same graph should produce same hash
+        Assert.Equal(result1.GraphHash, result2.GraphHash);
+    }
+
+    private static RichGraph CreateTestGraph()
+    {
+        return new RichGraph(
+            Nodes: new[]
+            {
+                new RichGraphNode(
+                    Id: "entry-1",
+                    SymbolId: "Handler.handle",
+                    CodeId: null,
+                    Purl: "pkg:maven/com.example/handler@1.0.0",
+                    Lang: "java",
+                    Kind: "http_handler",
+                    Display: "GET /api/users",
+                    BuildId: null,
+                    Evidence: null,
+                    Attributes: null,
+                    SymbolDigest: "sha256:entry1digest"),
+                new RichGraphNode(
+                    Id: "sink-1",
+                    SymbolId: "DB.executeQuery",
+                    CodeId: null,
+                    Purl: "pkg:maven/org.database/driver@2.0.0",
+                    Lang: "java",
+                    Kind: "sql_sink",
+                    Display: "executeQuery(String)",
+                    BuildId: null,
+                    Evidence: null,
+                    Attributes: new Dictionary<string, string> { ["is_sink"] = "true" },
+                    SymbolDigest: "sha256:sink1digest")
+            },
+            Edges: new[]
+            {
+                new RichGraphEdge(
+                    From: "entry-1",
+                    To: "sink-1",
+                    Kind: "call",
+                    Purl: null,
+                    SymbolDigest: null,
+                    Evidence: null,
+                    Confidence: 1.0,
+                    Candidates: null)
+            },
+            Roots: new[]
+            {
+                new RichGraphRoot("entry-1", "runtime", null)
+            },
+            Analyzer: new RichGraphAnalyzer("stellaops.scanner.reachability", "1.0.0", null),
+            Schema: "richgraph-v1"
+        );
+    }
+
+    /// <summary>
+    /// Test crypto hash implementation.
+    /// </summary>
+    private sealed class TestCryptoHash : ICryptoHash
+    {
+        public byte[] ComputeHash(ReadOnlySpan<byte> data, string? algorithmId = null)
+            => System.Security.Cryptography.SHA256.HashData(data);
+
+        public string ComputeHashHex(ReadOnlySpan<byte> data, string? algorithmId = null)
+            => Convert.ToHexString(ComputeHash(data, algorithmId)).ToLowerInvariant();
+
+        public string ComputeHashBase64(ReadOnlySpan<byte> data, string? algorithmId = null)
+            => Convert.ToBase64String(ComputeHash(data, algorithmId));
+
+        public async ValueTask<byte[]> ComputeHashAsync(Stream stream, string? algorithmId = null, CancellationToken cancellationToken = default)
+        {
+            using var buffer = new MemoryStream();
+            await stream.CopyToAsync(buffer, cancellationToken).ConfigureAwait(false);
+            return System.Security.Cryptography.SHA256.HashData(buffer.ToArray());
+        }
+
+        public async ValueTask<string> ComputeHashHexAsync(Stream stream, string? algorithmId = null, CancellationToken cancellationToken = default)
+        {
+            var hash = await ComputeHashAsync(stream, algorithmId, cancellationToken).ConfigureAwait(false);
+            return Convert.ToHexString(hash).ToLowerInvariant();
+        }
+
+        public byte[] ComputeHashForPurpose(ReadOnlySpan<byte> data, string purpose)
+            => ComputeHash(data);
+
+        public string ComputeHashHexForPurpose(ReadOnlySpan<byte> data, string purpose)
+            => ComputeHashHex(data);
+
+        public string ComputeHashBase64ForPurpose(ReadOnlySpan<byte> data, string purpose)
+            => ComputeHashBase64(data);
+
+        public async ValueTask<byte[]> ComputeHashForPurposeAsync(Stream stream, string purpose, CancellationToken cancellationToken = default)
+            => await ComputeHashAsync(stream, null, cancellationToken).ConfigureAwait(false);
+
+        public async ValueTask<string> ComputeHashHexForPurposeAsync(Stream stream, string purpose, CancellationToken cancellationToken = default)
+            => await ComputeHashHexAsync(stream, null, cancellationToken).ConfigureAwait(false);
+
+        public string GetAlgorithmForPurpose(string purpose) => "blake3";
+
+        public string GetHashPrefix(string purpose) => "blake3:";
+
+        public string ComputePrefixedHashForPurpose(ReadOnlySpan<byte> data, string purpose)
+            => $"blake3:{ComputeHashHex(data)}";
+    }
+}

src/Scanner/__Tests/StellaOps.Scanner.Reachability.Tests/Fixtures/graph-only.golden.json

@@ -0,0 +1,32 @@
+{
+  "_type": "https://in-toto.io/Statement/v1",
+  "subject": [
+    {
+      "name": "pkg:oci/test-image@sha256:abc123",
+      "digest": {
+        "sha256": "abc123def456789012345678901234567890123456789012345678901234"
+      }
+    }
+  ],
+  "predicateType": "https://stellaops.io/attestation/reachabilityWitness/v1",
+  "predicate": {
+    "version": "1.0.0",
+    "analysisTimestamp": "2025-01-01T00:00:00.0000000Z",
+    "analyzer": {
+      "name": "stellaops.scanner.reachability",
+      "version": "1.0.0"
+    },
+    "graph": {
+      "schema": "richgraph-v1",
+      "hash": "blake3:0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef",
+      "nodeCount": 3,
+      "edgeCount": 2
+    },
+    "summary": {
+      "sinkCount": 1,
+      "entrypointCount": 1,
+      "pathCount": 1,
+      "gateCoverage": 0.0
+    }
+  }
+}

src/Scanner/__Tests/StellaOps.Scanner.Reachability.Tests/Fixtures/graph-with-runtime.golden.json

@@ -0,0 +1,45 @@
+{
+  "_type": "https://in-toto.io/Statement/v1",
+  "subject": [
+    {
+      "name": "pkg:oci/production-app@sha256:xyz789",
+      "digest": {
+        "sha256": "xyz789abc123def456789012345678901234567890123456789012345678"
+      }
+    }
+  ],
+  "predicateType": "https://stellaops.io/attestation/reachabilityWitness/v1",
+  "predicate": {
+    "version": "1.0.0",
+    "analysisTimestamp": "2025-01-15T12:30:00.0000000Z",
+    "analyzer": {
+      "name": "stellaops.scanner.reachability",
+      "version": "1.0.0"
+    },
+    "graph": {
+      "schema": "richgraph-v1",
+      "hash": "blake3:fedcba9876543210fedcba9876543210fedcba9876543210fedcba9876543210",
+      "nodeCount": 150,
+      "edgeCount": 340,
+      "casUri": "cas://reachability/graphs/fedcba9876543210fedcba9876543210fedcba9876543210fedcba9876543210"
+    },
+    "summary": {
+      "sinkCount": 12,
+      "entrypointCount": 8,
+      "pathCount": 45,
+      "gateCoverage": 0.67
+    },
+    "policy": {
+      "hash": "sha256:policy123456789012345678901234567890123456789012345678901234"
+    },
+    "source": {
+      "commit": "a1b2c3d4e5f6a1b2c3d4e5f6a1b2c3d4e5f6a1b2"
+    },
+    "runtime": {
+      "observedAt": "2025-01-15T12:25:00.0000000Z",
+      "traceCount": 1250,
+      "coveredPaths": 38,
+      "runtimeConfidence": 0.84
+    }
+  }
+}

src/Scanner/__Tests/StellaOps.Scanner.Reachability.Tests/PathExplanationServiceTests.cs

@@ -206,15 +206,8 @@ public class PathExplanationServiceTests
 
     private static RichGraph CreateSimpleGraph()
     {
-        return new RichGraph
-        {
-            Schema = "stellaops.richgraph.v1",
-            Meta = new RichGraphMeta { Hash = "test-hash" },
-            Roots = new[]
-            {
-                new RichGraphRoot("entry-1", "runtime", null)
-            },
-            Nodes = new[]
+        return new RichGraph(
+            Nodes: new[]
             {
                 new RichGraphNode(
                     Id: "entry-1",
@@ -241,21 +234,23 @@ public class PathExplanationServiceTests
                     Attributes: new Dictionary<string, string> { ["is_sink"] = "true" },
                     SymbolDigest: null)
             },
-            Edges = new[]
+            Edges: new[]
             {
-                new RichGraphEdge("entry-1", "sink-1", "call", null)
-            }
-        };
+                new RichGraphEdge("entry-1", "sink-1", "call", null, null, null, 1.0, null)
+            },
+            Roots: new[]
+            {
+                new RichGraphRoot("entry-1", "runtime", null)
+            },
+            Analyzer: new RichGraphAnalyzer("test", "1.0", null),
+            Schema: "stellaops.richgraph.v1"
+        );
     }
 
     private static RichGraph CreateGraphWithMultipleSinks()
     {
-        return new RichGraph
-        {
-            Schema = "stellaops.richgraph.v1",
-            Meta = new RichGraphMeta { Hash = "test-hash" },
-            Roots = new[] { new RichGraphRoot("entry-1", "runtime", null) },
-            Nodes = new[]
+        return new RichGraph(
+            Nodes: new[]
             {
                 new RichGraphNode("entry-1", "Handler", null, null, "java", "handler", null, null, null, null, null),
                 new RichGraphNode("sink-1", "Sink1", null, null, "java", "sink", null, null, null,
@@ -263,12 +258,15 @@ public class PathExplanationServiceTests
                 new RichGraphNode("sink-2", "Sink2", null, null, "java", "sink", null, null, null,
                     new Dictionary<string, string> { ["is_sink"] = "true" }, null)
             },
-            Edges = new[]
+            Edges: new[]
             {
-                new RichGraphEdge("entry-1", "sink-1", "call", null),
-                new RichGraphEdge("entry-1", "sink-2", "call", null)
-            }
-        };
+                new RichGraphEdge("entry-1", "sink-1", "call", null, null, null, 1.0, null),
+                new RichGraphEdge("entry-1", "sink-2", "call", null, null, null, 1.0, null)
+            },
+            Roots: new[] { new RichGraphRoot("entry-1", "runtime", null) },
+            Analyzer: new RichGraphAnalyzer("test", "1.0", null),
+            Schema: "stellaops.richgraph.v1"
+        );
     }
 
     private static RichGraph CreateGraphWithGates()
@@ -285,22 +283,21 @@ public class PathExplanationServiceTests
             }
         };
 
-        return new RichGraph
-        {
-            Schema = "stellaops.richgraph.v1",
-            Meta = new RichGraphMeta { Hash = "test-hash" },
-            Roots = new[] { new RichGraphRoot("entry-1", "runtime", null) },
-            Nodes = new[]
+        return new RichGraph(
+            Nodes: new[]
             {
                 new RichGraphNode("entry-1", "Handler", null, null, "java", "handler", null, null, null, null, null),
                 new RichGraphNode("sink-1", "Sink", null, null, "java", "sink", null, null, null,
                     new Dictionary<string, string> { ["is_sink"] = "true" }, null)
             },
-            Edges = new[]
+            Edges: new[]
             {
-                new RichGraphEdge("entry-1", "sink-1", "call", gates)
-            }
-        };
+                new RichGraphEdge("entry-1", "sink-1", "call", null, null, null, 1.0, null, gates)
+            },
+            Roots: new[] { new RichGraphRoot("entry-1", "runtime", null) },
+            Analyzer: new RichGraphAnalyzer("test", "1.0", null),
+            Schema: "stellaops.richgraph.v1"
+        );
     }
 
     private static RichGraph CreateDeepGraph(int depth)
@@ -317,18 +314,17 @@ public class PathExplanationServiceTests
 
             if (i > 0)
             {
-                edges.Add(new RichGraphEdge($"node-{i - 1}", $"node-{i}", "call", null));
+                edges.Add(new RichGraphEdge($"node-{i - 1}", $"node-{i}", "call", null, null, null, 1.0, null));
             }
         }
 
-        return new RichGraph
-        {
-            Schema = "stellaops.richgraph.v1",
-            Meta = new RichGraphMeta { Hash = "test-hash" },
-            Roots = new[] { new RichGraphRoot("node-0", "runtime", null) },
-            Nodes = nodes,
-            Edges = edges
-        };
+        return new RichGraph(
+            Nodes: nodes,
+            Edges: edges,
+            Roots: new[] { new RichGraphRoot("node-0", "runtime", null) },
+            Analyzer: new RichGraphAnalyzer("test", "1.0", null),
+            Schema: "stellaops.richgraph.v1"
+        );
     }
 
     private static RichGraph CreateGraphWithMultiplePaths(int pathCount)
@@ -344,17 +340,16 @@ public class PathExplanationServiceTests
         {
             nodes.Add(new RichGraphNode($"sink-{i}", $"Sink{i}", null, null, "java", "sink", null, null, null,
                 new Dictionary<string, string> { ["is_sink"] = "true" }, null));
-            edges.Add(new RichGraphEdge("entry-1", $"sink-{i}", "call", null));
+            edges.Add(new RichGraphEdge("entry-1", $"sink-{i}", "call", null, null, null, 1.0, null));
         }
 
-        return new RichGraph
-        {
-            Schema = "stellaops.richgraph.v1",
-            Meta = new RichGraphMeta { Hash = "test-hash" },
-            Roots = new[] { new RichGraphRoot("entry-1", "runtime", null) },
-            Nodes = nodes,
-            Edges = edges
-        };
+        return new RichGraph(
+            Nodes: nodes,
+            Edges: edges,
+            Roots: new[] { new RichGraphRoot("entry-1", "runtime", null) },
+            Analyzer: new RichGraphAnalyzer("test", "1.0", null),
+            Schema: "stellaops.richgraph.v1"
+        );
     }
 
     private static ExplainedPath CreateTestPath()
@@ -364,7 +359,7 @@ public class PathExplanationServiceTests
             PathId = "entry:sink:0",
             SinkId = "sink-1",
             SinkSymbol = "DB.query",
-            SinkCategory = SinkCategory.SqlRaw,
+            SinkCategory = Explanation.SinkCategory.SqlRaw,
             EntrypointId = "entry-1",
             EntrypointSymbol = "Handler.handle",
             EntrypointType = EntrypointType.HttpEndpoint,
@@ -402,7 +397,7 @@ public class PathExplanationServiceTests
             PathId = "entry:sink:0",
             SinkId = "sink-1",
             SinkSymbol = "DB.query",
-            SinkCategory = SinkCategory.SqlRaw,
+            SinkCategory = Explanation.SinkCategory.SqlRaw,
             EntrypointId = "entry-1",
             EntrypointSymbol = "Handler.handle",
             EntrypointType = EntrypointType.HttpEndpoint,

src/Scanner/__Tests/StellaOps.Scanner.Reachability.Tests/RichGraphWriterTests.cs

@@ -132,6 +132,6 @@ public class RichGraphWriterTests
         
         // Verify meta.json also contains the blake3-prefixed hash
         var metaJson = await File.ReadAllTextAsync(result.MetaPath);
-        Assert.Contains("\"graph_hash\":\"blake3:", metaJson);
+        Assert.Contains("\"graph_hash\": \"blake3:", metaJson);
     }
 }

src/Web/StellaOps.Web/src/app/core/analytics/evidence-panel-metrics.service.spec.ts

@@ -10,14 +10,30 @@ import {
   EvidencePanelMetricsService,
   EvidencePanelAction,
 } from './evidence-panel-metrics.service';
-import { APP_CONFIG } from '../config/app.config';
+import { APP_CONFIG, AppConfig } from '../config/app-config.model';
 
 describe('EvidencePanelMetricsService', () => {
   let service: EvidencePanelMetricsService;
   let httpMock: HttpTestingController;
 
-  const mockConfig = {
-    apiBaseUrl: 'http://localhost:5000/api',
+  const mockConfig: AppConfig = {
+    authority: {
+      issuer: 'https://auth.stellaops.test/',
+      clientId: 'ui-client',
+      authorizeEndpoint: 'https://auth.stellaops.test/connect/authorize',
+      tokenEndpoint: 'https://auth.stellaops.test/connect/token',
+      redirectUri: 'https://ui.stellaops.test/auth/callback',
+      scope: 'openid profile email ui.read',
+      audience: 'https://scanner.stellaops.test',
+    },
+    apiBaseUrls: {
+      gateway: 'http://localhost:5000/api',
+      authority: 'https://auth.stellaops.test',
+      scanner: 'https://scanner.stellaops.test',
+      policy: 'https://policy.stellaops.test',
+      concelier: 'https://concelier.stellaops.test',
+      attestor: 'https://attestor.stellaops.test',
+    },
   };
 
   beforeEach(() => {
@@ -197,7 +213,7 @@ describe('EvidencePanelMetricsService', () => {
       }
 
       // Expect POST to metrics endpoint
-      const req = httpMock.expectOne(`${mockConfig.apiBaseUrl}/metrics/evidence-panel`);
+      const req = httpMock.expectOne(`${mockConfig.apiBaseUrls.gateway}/metrics/evidence-panel`);
       expect(req.request.method).toBe('POST');
       expect(req.request.body.sessions.length).toBe(10);
 
@@ -213,7 +229,7 @@ describe('EvidencePanelMetricsService', () => {
         service.endSession();
       }
 
-      const req = httpMock.expectOne(`${mockConfig.apiBaseUrl}/metrics/evidence-panel`);
+      const req = httpMock.expectOne(`${mockConfig.apiBaseUrls.gateway}/metrics/evidence-panel`);
       const sessions = req.request.body.sessions;
 
       expect(sessions[0]).toEqual(jasmine.objectContaining({

src/Web/StellaOps.Web/src/app/core/analytics/evidence-panel-metrics.service.ts

@@ -11,7 +11,7 @@
 
 import { Injectable, signal, computed, inject } from '@angular/core';
 import { HttpClient } from '@angular/common/http';
-import { APP_CONFIG, AppConfig } from '../config/app.config';
+import { APP_CONFIG, AppConfig } from '../config/app-config.model';
 
 /**
  * Types of actions tracked in the Evidence Panel
@@ -243,7 +243,7 @@ export class EvidencePanelMetricsService {
 
     // Fire-and-forget POST to metrics endpoint
     this.http.post(
-      `${this.config.apiBaseUrl}/metrics/evidence-panel`,
+      `${this.resolveMetricsBaseUrl()}/metrics/evidence-panel`,
       {
         sessions: sessions.map(s => ({
           sessionId: s.sessionId,
@@ -264,6 +264,10 @@ export class EvidencePanelMetricsService {
     });
   }
 
+  private resolveMetricsBaseUrl(): string {
+    return this.config.apiBaseUrls.gateway ?? this.config.apiBaseUrls.scanner;
+  }
+
   /**
    * Get current metrics summary for debugging/display
    */

src/Web/StellaOps.Web/src/app/core/api/triage-evidence.client.ts

@@ -194,11 +194,11 @@ export class TriageEvidenceHttpClient implements TriageEvidenceApi {
     }
   }
 
-  private buildParams(options?: Record<string, unknown>): HttpParams {
+  private buildParams(options?: object): HttpParams {
     let params = new HttpParams();
 
     if (options) {
-      for (const [key, value] of Object.entries(options)) {
+      for (const [key, value] of Object.entries(options as Record<string, unknown>)) {
         if (value !== undefined && value !== null && key !== 'tenantId' && key !== 'traceId') {
           params = params.set(key, String(value));
         }

src/Web/StellaOps.Web/src/app/core/telemetry/telemetry-sampler.service.ts

@@ -83,13 +83,15 @@ export class TelemetrySamplerService {
   }
 
   private createSessionId(): string {
-    if (typeof crypto !== 'undefined' && 'randomUUID' in crypto) {
-      return crypto.randomUUID();
+    const cryptoApi = this.getCryptoApi();
+
+    if (cryptoApi?.randomUUID) {
+      return cryptoApi.randomUUID();
     }
 
-    if (typeof crypto !== 'undefined' && 'getRandomValues' in crypto) {
+    if (cryptoApi?.getRandomValues) {
       const bytes = new Uint8Array(16);
-      crypto.getRandomValues(bytes);
+      cryptoApi.getRandomValues(bytes);
       return Array.from(bytes, (b) => b.toString(16).padStart(2, '0')).join('');
     }
 
@@ -97,13 +99,21 @@ export class TelemetrySamplerService {
   }
 
   private createSampleValue(): number {
-    if (typeof crypto !== 'undefined' && 'getRandomValues' in crypto) {
+    const cryptoApi = this.getCryptoApi();
+
+    if (cryptoApi?.getRandomValues) {
       const bytes = new Uint32Array(1);
-      crypto.getRandomValues(bytes);
+      cryptoApi.getRandomValues(bytes);
       return bytes[0] / 0x1_0000_0000;
     }
 
     return Math.random();
   }
-}
 
+  private getCryptoApi(): Crypto | null {
+    if (typeof globalThis === 'undefined') return null;
+
+    const value = (globalThis as unknown as { crypto?: Crypto }).crypto;
+    return value ?? null;
+  }
+}

src/Web/StellaOps.Web/src/app/features/evidence/evidence-panel.component.spec.ts

@@ -1,8 +1,10 @@
 import { ComponentFixture, TestBed } from '@angular/core/testing';
+import { HttpClientTestingModule } from '@angular/common/http/testing';
 
 import type { EvidenceApi } from '../../core/api/evidence.client';
 import { EVIDENCE_API } from '../../core/api/evidence.client';
 import type { EvidenceData, VexDecision, VexStatus } from '../../core/api/evidence.models';
+import { APP_CONFIG, type AppConfig } from '../../core/config/app-config.model';
 import { EvidencePanelComponent } from './evidence-panel.component';
 
 function createVexDecision(status: VexStatus, id: string): VexDecision {
@@ -32,8 +34,31 @@ describe('EvidencePanelComponent', () => {
     ]);
 
     await TestBed.configureTestingModule({
-      imports: [EvidencePanelComponent],
-      providers: [{ provide: EVIDENCE_API, useValue: api }],
+      imports: [HttpClientTestingModule, EvidencePanelComponent],
+      providers: [
+        { provide: EVIDENCE_API, useValue: api },
+        {
+          provide: APP_CONFIG,
+          useValue: {
+            authority: {
+              issuer: 'https://auth.stellaops.test/',
+              clientId: 'ui-client',
+              authorizeEndpoint: 'https://auth.stellaops.test/connect/authorize',
+              tokenEndpoint: 'https://auth.stellaops.test/connect/token',
+              redirectUri: 'https://ui.stellaops.test/auth/callback',
+              scope: 'openid profile email ui.read',
+              audience: 'https://scanner.stellaops.test',
+            },
+            apiBaseUrls: {
+              authority: 'https://auth.stellaops.test',
+              scanner: 'https://scanner.stellaops.test',
+              policy: 'https://policy.stellaops.test',
+              concelier: 'https://concelier.stellaops.test',
+              attestor: 'https://attestor.stellaops.test',
+            },
+          } satisfies AppConfig,
+        },
+      ],
     }).compileComponents();
 
     fixture = TestBed.createComponent(EvidencePanelComponent);

src/Web/StellaOps.Web/src/app/features/reachability/components/path-viewer/index.ts

@@ -0,0 +1,4 @@
+/**
+ * PathViewerComponent barrel export
+ */
+export * from './path-viewer.component';

src/Web/StellaOps.Web/src/app/features/reachability/components/path-viewer/path-viewer.component.html

@@ -0,0 +1,110 @@
+<!--
+  PathViewerComponent Template
+  Sprint: SPRINT_3600_0004_0001_ui_evidence_chain
+  Task: UI-003
+-->
+<div class="path-viewer" [class.path-viewer--collapsed]="collapsed()">
+  <!-- Header -->
+  <div class="path-viewer__header">
+    <span class="path-viewer__title">{{ title() }}</span>
+    <div class="path-viewer__actions">
+      @if (hiddenNodeCount() > 0) {
+        <button
+          type="button"
+          class="path-viewer__btn path-viewer__btn--expand"
+          (click)="toggleExpand()"
+          [attr.aria-expanded]="isExpanded()">
+          @if (isExpanded()) {
+            Collapse ({{ hiddenNodeCount() }} hidden)
+          } @else {
+            Expand (+{{ hiddenNodeCount() }} nodes)
+          }
+        </button>
+      }
+      @if (collapsible()) {
+        <button
+          type="button"
+          class="path-viewer__btn path-viewer__btn--collapse"
+          (click)="toggleCollapse()"
+          [attr.aria-expanded]="!collapsed()">
+          {{ collapsed() ? 'Show' : 'Hide' }}
+        </button>
+      }
+    </div>
+  </div>
+
+  <!-- Content -->
+  @if (!collapsed()) {
+    <div class="path-viewer__content">
+      <!-- Path visualization -->
+      <ol class="path-viewer__nodes" role="list">
+        @for (node of displayNodes(); track node.nodeId; let i = $index; let last = $last) {
+          <!-- Node -->
+          <li
+            [class]="getNodeClass(node)"
+            (click)="onNodeClick(node)"
+            (keydown.enter)="onNodeClick(node)"
+            tabindex="0"
+            role="listitem"
+            [attr.aria-label]="node.symbol">
+            <span class="path-node__icon" [attr.aria-hidden]="true">
+              {{ getNodeIcon(node) }}
+            </span>
+            <div class="path-node__details">
+              <span class="path-node__symbol">{{ node.symbol }}</span>
+              @if (node.file) {
+                <span class="path-node__location">
+                  {{ node.file }}@if (node.line) {:{{ node.line }}}
+                </span>
+              }
+              @if (node.package) {
+                <span class="path-node__package">{{ node.package }}</span>
+              }
+              @if (showConfidence() && node.confidence !== undefined) {
+                <span class="path-node__confidence">
+                  {{ formatConfidence(node.confidence) }}
+                </span>
+              }
+              @if (highlightChanges() && node.isChanged && node.changeKind) {
+                <span class="path-node__change-badge" [class]="'path-node__change-badge--' + node.changeKind">
+                  {{ formatChangeKind(node.changeKind) }}
+                </span>
+              }
+              @if (node.nodeType === 'entrypoint') {
+                <span class="path-node__type-badge path-node__type-badge--entrypoint">
+                  ENTRYPOINT
+                </span>
+              }
+              @if (node.nodeType === 'sink') {
+                <span class="path-node__type-badge path-node__type-badge--sink">
+                  SINK
+                </span>
+              }
+              @if (node.nodeType === 'gate') {
+                <span class="path-node__type-badge path-node__type-badge--gate">
+                  GATE
+                </span>
+              }
+            </div>
+          </li>
+
+          <!-- Connector -->
+          @if (!last) {
+            <li class="path-viewer__connector" role="presentation" aria-hidden="true">
+              <span class="path-viewer__connector-line"></span>
+            </li>
+          }
+        }
+      </ol>
+
+      <!-- Hidden nodes indicator -->
+      @if (hiddenNodeCount() > 0 && !isExpanded()) {
+        <div class="path-viewer__hidden-indicator">
+          <span class="path-viewer__hidden-text">
+            … {{ hiddenNodeCount() }} intermediate node(s) hidden …
+          </span>
+        </div>
+      }
+    </div>
+  }
+</div>

src/Web/StellaOps.Web/src/app/features/reachability/components/path-viewer/path-viewer.component.scss

@@ -0,0 +1,296 @@
+/**
+ * PathViewerComponent Styles
+ * Sprint: SPRINT_3600_0004_0001_ui_evidence_chain
+ * Task: UI-004
+ */
+
+// Variables
+$color-entrypoint: #10b981; // Green
+$color-sink: #ef4444; // Red
+$color-gate: #f59e0b; // Amber
+$color-changed: #8b5cf6; // Purple
+$color-added: #22c55e;
+$color-removed: #ef4444;
+$color-modified: #f59e0b;
+$color-border: #e5e7eb;
+$color-bg: #ffffff;
+$color-bg-hover: #f9fafb;
+$color-text: #111827;
+$color-text-muted: #6b7280;
+
+.path-viewer {
+  font-family: var(--font-family-sans, system-ui, sans-serif);
+  background: $color-bg;
+  border: 1px solid $color-border;
+  border-radius: 8px;
+  overflow: hidden;
+
+  &--collapsed {
+    .path-viewer__content {
+      display: none;
+    }
+  }
+
+  &__header {
+    display: flex;
+    justify-content: space-between;
+    align-items: center;
+    padding: 12px 16px;
+    border-bottom: 1px solid $color-border;
+    background: #f9fafb;
+  }
+
+  &__title {
+    font-weight: 600;
+    font-size: 14px;
+    color: $color-text;
+  }
+
+  &__actions {
+    display: flex;
+    gap: 8px;
+  }
+
+  &__btn {
+    padding: 4px 12px;
+    font-size: 12px;
+    font-weight: 500;
+    border: 1px solid $color-border;
+    border-radius: 4px;
+    background: $color-bg;
+    color: $color-text-muted;
+    cursor: pointer;
+    transition: all 0.15s ease;
+
+    &:hover {
+      background: $color-bg-hover;
+      color: $color-text;
+    }
+
+    &:focus-visible {
+      outline: 2px solid #3b82f6;
+      outline-offset: 2px;
+    }
+
+    &--expand {
+      color: #3b82f6;
+      border-color: #3b82f6;
+
+      &:hover {
+        background: #eff6ff;
+      }
+    }
+  }
+
+  &__content {
+    padding: 16px;
+  }
+
+  &__nodes {
+    list-style: none;
+    margin: 0;
+    padding: 0;
+  }
+
+  &__connector {
+    display: flex;
+    justify-content: center;
+    padding: 4px 0;
+
+    &-line {
+      width: 2px;
+      height: 16px;
+      background: $color-border;
+    }
+  }
+
+  &__hidden-indicator {
+    display: flex;
+    justify-content: center;
+    padding: 8px 0;
+  }
+
+  &__hidden-text {
+    font-size: 12px;
+    font-style: italic;
+    color: $color-text-muted;
+  }
+}
+
+.path-node {
+  display: flex;
+  align-items: flex-start;
+  gap: 12px;
+  padding: 12px;
+  border: 1px solid $color-border;
+  border-radius: 6px;
+  background: $color-bg;
+  cursor: pointer;
+  transition: all 0.15s ease;
+
+  &:hover {
+    background: $color-bg-hover;
+    border-color: #d1d5db;
+  }
+
+  &:focus-visible {
+    outline: 2px solid #3b82f6;
+    outline-offset: 2px;
+  }
+
+  &__icon {
+    flex-shrink: 0;
+    width: 24px;
+    height: 24px;
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    font-size: 14px;
+    border-radius: 50%;
+    background: #f3f4f6;
+    color: $color-text-muted;
+  }
+
+  &__details {
+    flex: 1;
+    display: flex;
+    flex-direction: column;
+    gap: 4px;
+  }
+
+  &__symbol {
+    font-weight: 500;
+    font-size: 14px;
+    font-family: var(--font-family-mono, 'SF Mono', Consolas, monospace);
+    color: $color-text;
+    word-break: break-word;
+  }
+
+  &__location {
+    font-size: 12px;
+    color: $color-text-muted;
+    font-family: var(--font-family-mono, 'SF Mono', Consolas, monospace);
+  }
+
+  &__package {
+    font-size: 11px;
+    color: $color-text-muted;
+    background: #f3f4f6;
+    padding: 2px 6px;
+    border-radius: 4px;
+    width: fit-content;
+  }
+
+  &__confidence {
+    font-size: 11px;
+    color: $color-text-muted;
+    background: #e0e7ff;
+    padding: 2px 6px;
+    border-radius: 4px;
+    width: fit-content;
+  }
+
+  &__change-badge {
+    font-size: 10px;
+    font-weight: 600;
+    text-transform: uppercase;
+    letter-spacing: 0.05em;
+    padding: 2px 6px;
+    border-radius: 4px;
+    width: fit-content;
+
+    &--added {
+      background: #dcfce7;
+      color: #166534;
+    }
+
+    &--removed {
+      background: #fee2e2;
+      color: #991b1b;
+    }
+
+    &--modified {
+      background: #fef3c7;
+      color: #92400e;
+    }
+  }
+
+  &__type-badge {
+    font-size: 10px;
+    font-weight: 600;
+    text-transform: uppercase;
+    letter-spacing: 0.05em;
+    padding: 2px 6px;
+    border-radius: 4px;
+    width: fit-content;
+
+    &--entrypoint {
+      background: #d1fae5;
+      color: #065f46;
+    }
+
+    &--sink {
+      background: #fee2e2;
+      color: #991b1b;
+    }
+
+    &--gate {
+      background: #fef3c7;
+      color: #92400e;
+    }
+  }
+
+  // Node type variants
+  &--entrypoint {
+    border-color: $color-entrypoint;
+
+    .path-node__icon {
+      background: #d1fae5;
+      color: $color-entrypoint;
+    }
+  }
+
+  &--sink {
+    border-color: $color-sink;
+
+    .path-node__icon {
+      background: #fee2e2;
+      color: $color-sink;
+    }
+  }
+
+  &--gate {
+    border-color: $color-gate;
+
+    .path-node__icon {
+      background: #fef3c7;
+      color: $color-gate;
+    }
+  }
+
+  // Changed state
+  &--changed {
+    border-color: $color-changed;
+    background: #faf5ff;
+
+    .path-node__icon {
+      background: #ede9fe;
+      color: $color-changed;
+    }
+  }
+
+  &--added {
+    border-color: $color-added;
+    background: #f0fdf4;
+  }
+
+  &--removed {
+    border-color: $color-removed;
+    background: #fef2f2;
+  }
+
+  &--modified {
+    border-color: $color-modified;
+    background: #fffbeb;
+  }
+}

src/Web/StellaOps.Web/src/app/features/reachability/components/path-viewer/path-viewer.component.ts

@@ -0,0 +1,155 @@
+/**
+ * PathViewerComponent - Call Path Visualization
+ * Sprint: SPRINT_3600_0004_0001_ui_evidence_chain
+ * Task: UI-003
+ */
+
+import { Component, input, output, computed, signal } from '@angular/core';
+import { CommonModule } from '@angular/common';
+import { CompressedPath, PathNode, ExpandedPath, PathEdge } from '../../models/path-viewer.models';
+
+/**
+ * Visualizes reachability call paths from entrypoint to sink.
+ * Supports both compressed and expanded views.
+ *
+ * @example
+ * ```html
+ * <app-path-viewer
+ *   [path]="compressedPath"
+ *   [collapsible]="true"
+ *   [showConfidence]="true"
+ *   (nodeClick)="onNodeClick($event)"
+ *   (expandRequest)="onExpandPath($event)">
+ * </app-path-viewer>
+ * ```
+ */
+@Component({
+  selector: 'app-path-viewer',
+  standalone: true,
+  imports: [CommonModule],
+  templateUrl: './path-viewer.component.html',
+  styleUrl: './path-viewer.component.scss'
+})
+export class PathViewerComponent {
+  /** The compressed path to display */
+  path = input.required<CompressedPath>();
+
+  /** Optional title for the path viewer */
+  title = input<string>('Reachability Path');
+
+  /** Whether the viewer can be collapsed */
+  collapsible = input<boolean>(true);
+
+  /** Whether to show confidence scores */
+  showConfidence = input<boolean>(false);
+
+  /** Whether to highlight changed nodes */
+  highlightChanges = input<boolean>(true);
+
+  /** Maximum depth to show before collapsing */
+  maxVisibleDepth = input<number>(5);
+
+  /** Emits when a node is clicked */
+  nodeClick = output<PathNode>();
+
+  /** Emits when path expansion is requested */
+  expandRequest = output<string>();
+
+  /** Internal collapsed state */
+  collapsed = signal<boolean>(false);
+
+  /** Whether the full path is expanded */
+  isExpanded = signal<boolean>(false);
+
+  /** Computed: effective nodes to display */
+  displayNodes = computed(() => {
+    const p = this.path();
+    if (this.isExpanded()) {
+      return this.buildFullNodeList(p);
+    }
+    return [p.entrypoint, ...p.keyNodes, p.sink];
+  });
+
+  /** Computed: count of hidden nodes */
+  hiddenNodeCount = computed(() => {
+    const p = this.path();
+    if (this.isExpanded()) {
+      return 0;
+    }
+    return Math.max(0, p.intermediateCount - p.keyNodes.length);
+  });
+
+  /** Toggle collapsed state */
+  toggleCollapse(): void {
+    this.collapsed.update(v => !v);
+  }
+
+  /** Toggle expanded state */
+  toggleExpand(): void {
+    const p = this.path();
+    if (!this.isExpanded() && p.fullPath && p.fullPath.length > 0) {
+      this.expandRequest.emit(p.fullPath[0]);
+    }
+    this.isExpanded.update(v => !v);
+  }
+
+  /** Handle node click */
+  onNodeClick(node: PathNode): void {
+    this.nodeClick.emit(node);
+  }
+
+  /** Get CSS class for node type */
+  getNodeClass(node: PathNode): string {
+    const classes: string[] = ['path-node'];
+
+    if (node.nodeType) {
+      classes.push(`path-node--${node.nodeType}`);
+    }
+
+    if (this.highlightChanges() && node.isChanged) {
+      classes.push('path-node--changed');
+      if (node.changeKind) {
+        classes.push(`path-node--${node.changeKind}`);
+      }
+    }
+
+    return classes.join(' ');
+  }
+
+  /** Get icon for node type */
+  getNodeIcon(node: PathNode): string {
+    if (node.isChanged) {
+      return '●';
+    }
+
+    switch (node.nodeType) {
+      case 'entrypoint':
+        return '▶';
+      case 'sink':
+        return '⚠';
+      case 'gate':
+        return '◆';
+      default:
+        return '○';
+    }
+  }
+
+  /** Format change kind for display */
+  formatChangeKind(kind?: string): string {
+    if (!kind) return '';
+    return kind.charAt(0).toUpperCase() + kind.slice(1);
+  }
+
+  /** Format confidence as percentage */
+  formatConfidence(confidence?: number): string {
+    if (confidence === undefined) return '';
+    return `${Math.round(confidence * 100)}%`;
+  }
+
+  /** Build full node list from path */
+  private buildFullNodeList(path: CompressedPath): PathNode[] {
+    // For now, return compressed representation
+    // Full expansion requires additional data
+    return [path.entrypoint, ...path.keyNodes, path.sink];
+  }
+}

src/Web/StellaOps.Web/src/app/features/reachability/components/risk-drift-card/index.ts

@@ -0,0 +1,4 @@
+/**
+ * RiskDriftCardComponent barrel export
+ */
+export * from './risk-drift-card.component';

src/Web/StellaOps.Web/src/app/features/reachability/components/risk-drift-card/risk-drift-card.component.html

@@ -0,0 +1,136 @@
+<!--
+  RiskDriftCardComponent Template
+  Sprint: SPRINT_3600_0004_0001_ui_evidence_chain
+  Task: UI-007
+-->
+<article class="risk-drift-card" [class.risk-drift-card--compact]="compact()">
+  <!-- Header -->
+  <header class="risk-drift-card__header">
+    <div class="risk-drift-card__title">
+      <h3 class="risk-drift-card__heading">Reachability Drift</h3>
+      @if (showAttestation() && isSigned()) {
+        <span class="risk-drift-card__attestation-badge" title="Signed with DSSE">
+          ✓ Attested
+        </span>
+      }
+    </div>
+    <time class="risk-drift-card__time" [attr.datetime]="drift().comparedAt">
+      {{ formatTime(drift().comparedAt) }}
+    </time>
+  </header>
+
+  <!-- Summary metrics -->
+  <div class="risk-drift-card__summary">
+    <!-- Risk trend -->
+    <div class="risk-drift-card__metric risk-drift-card__metric--trend">
+      <span class="risk-drift-card__trend" [class]="trendClass()">
+        <span class="risk-drift-card__trend-icon">{{ trendIcon() }}</span>
+        <span class="risk-drift-card__trend-label">
+          {{ summary().riskTrend | titlecase }}
+        </span>
+      </span>
+      <span class="risk-drift-card__delta" [class.positive]="summary().netRiskDelta > 0" [class.negative]="summary().netRiskDelta < 0">
+        {{ formatRiskDelta(summary().netRiskDelta) }}
+      </span>
+    </div>
+
+    <!-- Key stats -->
+    @if (!compact()) {
+      <div class="risk-drift-card__stats">
+        <div class="risk-drift-card__stat">
+          <span class="risk-drift-card__stat-value">{{ summary().increasedReachability }}</span>
+          <span class="risk-drift-card__stat-label">Increased</span>
+        </div>
+        <div class="risk-drift-card__stat">
+          <span class="risk-drift-card__stat-value">{{ summary().decreasedReachability }}</span>
+          <span class="risk-drift-card__stat-label">Decreased</span>
+        </div>
+        <div class="risk-drift-card__stat">
+          <span class="risk-drift-card__stat-value">{{ summary().newSinks }}</span>
+          <span class="risk-drift-card__stat-label">New</span>
+        </div>
+        <div class="risk-drift-card__stat">
+          <span class="risk-drift-card__stat-value">{{ summary().removedSinks }}</span>
+          <span class="risk-drift-card__stat-label">Removed</span>
+        </div>
+      </div>
+    }
+
+    <!-- Severity breakdown -->
+    <div class="risk-drift-card__severity-bar">
+      @if (summary().bySeverity.critical > 0) {
+        <span class="risk-drift-card__severity risk-drift-card__severity--critical" [title]="'Critical: ' + summary().bySeverity.critical">
+          {{ summary().bySeverity.critical }}
+        </span>
+      }
+      @if (summary().bySeverity.high > 0) {
+        <span class="risk-drift-card__severity risk-drift-card__severity--high" [title]="'High: ' + summary().bySeverity.high">
+          {{ summary().bySeverity.high }}
+        </span>
+      }
+      @if (summary().bySeverity.medium > 0) {
+        <span class="risk-drift-card__severity risk-drift-card__severity--medium" [title]="'Medium: ' + summary().bySeverity.medium">
+          {{ summary().bySeverity.medium }}
+        </span>
+      }
+      @if (summary().bySeverity.low > 0) {
+        <span class="risk-drift-card__severity risk-drift-card__severity--low" [title]="'Low: ' + summary().bySeverity.low">
+          {{ summary().bySeverity.low }}
+        </span>
+      }
+    </div>
+  </div>
+
+  <!-- Preview sinks -->
+  @if (!compact() && previewSinks().length > 0) {
+    <div class="risk-drift-card__preview">
+      <h4 class="risk-drift-card__preview-title">Top Drifted Sinks</h4>
+      <ul class="risk-drift-card__sink-list">
+        @for (sink of previewSinks(); track sink.sink.nodeId) {
+          <li
+            class="risk-drift-card__sink-item"
+            (click)="onSinkClick(sink)"
+            (keydown.enter)="onSinkClick(sink)"
+            tabindex="0"
+            role="button">
+            <span class="risk-drift-card__sink-icon" [class]="getSeverityClass(sink.severity)">
+              @if (sink.isRiskIncrease) { ↑ } @else { ↓ }
+            </span>
+            <div class="risk-drift-card__sink-details">
+              <span class="risk-drift-card__sink-name">{{ sink.sink.symbol }}</span>
+              @if (sink.cveId) {
+                <span class="risk-drift-card__sink-cve">{{ sink.cveId }}</span>
+              }
+              <span class="risk-drift-card__sink-bucket">
+                {{ getBucketLabel(sink.previousBucket) }} → {{ getBucketLabel(sink.currentBucket) }}
+              </span>
+            </div>
+            <span class="risk-drift-card__sink-delta" [class.positive]="sink.riskDelta > 0" [class.negative]="sink.riskDelta < 0">
+              {{ formatRiskDelta(sink.riskDelta) }}
+            </span>
+          </li>
+        }
+      </ul>
+      @if (additionalSinksCount() > 0) {
+        <p class="risk-drift-card__more">
+          +{{ additionalSinksCount() }} more sinks
+        </p>
+      }
+    </div>
+  }
+
+  <!-- Actions -->
+  <footer class="risk-drift-card__footer">
+    @if (drift().pullRequestNumber) {
+      <span class="risk-drift-card__pr">
+        PR #{{ drift().pullRequestNumber }}
+      </span>
+    }
+    <button
+      type="button"
+      class="risk-drift-card__btn"
+      (click)="onViewDetails()">
+      View Details
+    </button>
+  </footer>
+</article>

src/Web/StellaOps.Web/src/app/features/reachability/components/risk-drift-card/risk-drift-card.component.scss

@@ -0,0 +1,348 @@
+/**
+ * RiskDriftCardComponent Styles
+ * Sprint: SPRINT_3600_0004_0001_ui_evidence_chain
+ * Task: UI-008
+ */
+
+// Variables
+$color-critical: #dc2626;
+$color-high: #ea580c;
+$color-medium: #d97706;
+$color-low: #ca8a04;
+$color-info: #6b7280;
+$color-positive: #dc2626; // risk increase is bad
+$color-negative: #16a34a; // risk decrease is good
+$color-border: #e5e7eb;
+$color-bg: #ffffff;
+$color-bg-hover: #f9fafb;
+$color-text: #111827;
+$color-text-muted: #6b7280;
+
+.risk-drift-card {
+  font-family: var(--font-family-sans, system-ui, sans-serif);
+  background: $color-bg;
+  border: 1px solid $color-border;
+  border-radius: 12px;
+  overflow: hidden;
+  box-shadow: 0 1px 3px rgba(0, 0, 0, 0.1);
+
+  &--compact {
+    .risk-drift-card__preview,
+    .risk-drift-card__stats {
+      display: none;
+    }
+  }
+
+  &__header {
+    display: flex;
+    justify-content: space-between;
+    align-items: center;
+    padding: 16px 20px;
+    border-bottom: 1px solid $color-border;
+    background: #fafafa;
+  }
+
+  &__title {
+    display: flex;
+    align-items: center;
+    gap: 12px;
+  }
+
+  &__heading {
+    margin: 0;
+    font-size: 16px;
+    font-weight: 600;
+    color: $color-text;
+  }
+
+  &__attestation-badge {
+    font-size: 11px;
+    font-weight: 500;
+    color: #059669;
+    background: #d1fae5;
+    padding: 2px 8px;
+    border-radius: 9999px;
+  }
+
+  &__time {
+    font-size: 12px;
+    color: $color-text-muted;
+  }
+
+  &__summary {
+    padding: 20px;
+    display: flex;
+    flex-direction: column;
+    gap: 16px;
+  }
+
+  &__metric--trend {
+    display: flex;
+    justify-content: space-between;
+    align-items: center;
+  }
+
+  &__trend {
+    display: flex;
+    align-items: center;
+    gap: 8px;
+    font-weight: 600;
+    font-size: 18px;
+
+    &--increasing {
+      color: $color-positive;
+    }
+
+    &--decreasing {
+      color: $color-negative;
+    }
+
+    &--stable {
+      color: $color-text-muted;
+    }
+  }
+
+  &__trend-icon {
+    font-size: 24px;
+  }
+
+  &__delta {
+    font-size: 24px;
+    font-weight: 700;
+    font-family: var(--font-family-mono, 'SF Mono', Consolas, monospace);
+
+    &.positive {
+      color: $color-positive;
+    }
+
+    &.negative {
+      color: $color-negative;
+    }
+  }
+
+  &__stats {
+    display: grid;
+    grid-template-columns: repeat(4, 1fr);
+    gap: 16px;
+    padding-top: 16px;
+    border-top: 1px solid $color-border;
+  }
+
+  &__stat {
+    display: flex;
+    flex-direction: column;
+    align-items: center;
+    text-align: center;
+  }
+
+  &__stat-value {
+    font-size: 20px;
+    font-weight: 600;
+    color: $color-text;
+  }
+
+  &__stat-label {
+    font-size: 11px;
+    color: $color-text-muted;
+    text-transform: uppercase;
+    letter-spacing: 0.05em;
+  }
+
+  &__severity-bar {
+    display: flex;
+    gap: 8px;
+  }
+
+  &__severity {
+    font-size: 12px;
+    font-weight: 600;
+    padding: 4px 10px;
+    border-radius: 9999px;
+    color: white;
+
+    &--critical {
+      background: $color-critical;
+    }
+
+    &--high {
+      background: $color-high;
+    }
+
+    &--medium {
+      background: $color-medium;
+    }
+
+    &--low {
+      background: $color-low;
+    }
+
+    &--info {
+      background: $color-info;
+    }
+  }
+
+  &__preview {
+    padding: 0 20px 20px;
+  }
+
+  &__preview-title {
+    margin: 0 0 12px;
+    font-size: 12px;
+    font-weight: 600;
+    text-transform: uppercase;
+    letter-spacing: 0.05em;
+    color: $color-text-muted;
+  }
+
+  &__sink-list {
+    list-style: none;
+    margin: 0;
+    padding: 0;
+    display: flex;
+    flex-direction: column;
+    gap: 8px;
+  }
+
+  &__sink-item {
+    display: flex;
+    align-items: center;
+    gap: 12px;
+    padding: 12px;
+    border: 1px solid $color-border;
+    border-radius: 8px;
+    cursor: pointer;
+    transition: all 0.15s ease;
+
+    &:hover {
+      background: $color-bg-hover;
+      border-color: #d1d5db;
+    }
+
+    &:focus-visible {
+      outline: 2px solid #3b82f6;
+      outline-offset: 2px;
+    }
+  }
+
+  &__sink-icon {
+    flex-shrink: 0;
+    width: 28px;
+    height: 28px;
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    font-size: 14px;
+    font-weight: 600;
+    border-radius: 50%;
+    background: #f3f4f6;
+    color: $color-text-muted;
+
+    &.risk-drift-card__severity--critical {
+      background: #fee2e2;
+      color: $color-critical;
+    }
+
+    &.risk-drift-card__severity--high {
+      background: #ffedd5;
+      color: $color-high;
+    }
+
+    &.risk-drift-card__severity--medium {
+      background: #fef3c7;
+      color: $color-medium;
+    }
+
+    &.risk-drift-card__severity--low {
+      background: #fef9c3;
+      color: $color-low;
+    }
+  }
+
+  &__sink-details {
+    flex: 1;
+    display: flex;
+    flex-direction: column;
+    gap: 2px;
+    min-width: 0;
+  }
+
+  &__sink-name {
+    font-weight: 500;
+    font-size: 14px;
+    font-family: var(--font-family-mono, 'SF Mono', Consolas, monospace);
+    color: $color-text;
+    white-space: nowrap;
+    overflow: hidden;
+    text-overflow: ellipsis;
+  }
+
+  &__sink-cve {
+    font-size: 12px;
+    color: $color-critical;
+    font-weight: 500;
+  }
+
+  &__sink-bucket {
+    font-size: 11px;
+    color: $color-text-muted;
+  }
+
+  &__sink-delta {
+    font-size: 14px;
+    font-weight: 600;
+    font-family: var(--font-family-mono, 'SF Mono', Consolas, monospace);
+
+    &.positive {
+      color: $color-positive;
+    }
+
+    &.negative {
+      color: $color-negative;
+    }
+  }
+
+  &__more {
+    margin: 8px 0 0;
+    font-size: 12px;
+    color: $color-text-muted;
+    text-align: center;
+  }
+
+  &__footer {
+    display: flex;
+    justify-content: space-between;
+    align-items: center;
+    padding: 12px 20px;
+    border-top: 1px solid $color-border;
+    background: #fafafa;
+  }
+
+  &__pr {
+    font-size: 12px;
+    color: $color-text-muted;
+    background: #f3f4f6;
+    padding: 4px 10px;
+    border-radius: 4px;
+  }
+
+  &__btn {
+    padding: 8px 16px;
+    font-size: 14px;
+    font-weight: 500;
+    color: #3b82f6;
+    background: transparent;
+    border: 1px solid #3b82f6;
+    border-radius: 6px;
+    cursor: pointer;
+    transition: all 0.15s ease;
+
+    &:hover {
+      background: #eff6ff;
+    }
+
+    &:focus-visible {
+      outline: 2px solid #3b82f6;
+      outline-offset: 2px;
+    }
+  }
+}

src/Web/StellaOps.Web/src/app/features/reachability/components/risk-drift-card/risk-drift-card.component.ts

@@ -0,0 +1,137 @@
+/**
+ * RiskDriftCardComponent - Drift Summary Card
+ * Sprint: SPRINT_3600_0004_0001_ui_evidence_chain
+ * Task: UI-007
+ */
+
+import { Component, input, output, computed } from '@angular/core';
+import { CommonModule } from '@angular/common';
+import { DriftResult, DriftSummary, DriftedSink } from '../../models/drift.models';
+
+/**
+ * Summary card showing reachability drift results.
+ * Displays risk trend, key metrics, and links to details.
+ *
+ * @example
+ * ```html
+ * <app-risk-drift-card
+ *   [drift]="driftResult"
+ *   [compact]="true"
+ *   (viewDetails)="onViewDetails()"
+ *   (sinkClick)="onSinkClick($event)">
+ * </app-risk-drift-card>
+ * ```
+ */
+@Component({
+  selector: 'app-risk-drift-card',
+  standalone: true,
+  imports: [CommonModule],
+  templateUrl: './risk-drift-card.component.html',
+  styleUrl: './risk-drift-card.component.scss'
+})
+export class RiskDriftCardComponent {
+  /** The drift result to display */
+  drift = input.required<DriftResult>();
+
+  /** Compact mode (less detail) */
+  compact = input<boolean>(false);
+
+  /** Whether to show attestation badge */
+  showAttestation = input<boolean>(true);
+
+  /** Maximum sinks to show in preview */
+  maxPreviewSinks = input<number>(3);
+
+  /** Emits when "View Details" is clicked */
+  viewDetails = output<void>();
+
+  /** Emits when a specific sink is clicked */
+  sinkClick = output<DriftedSink>();
+
+  /** Computed: summary from drift */
+  summary = computed<DriftSummary>(() => this.drift().summary);
+
+  /** Computed: is signed with DSSE */
+  isSigned = computed(() => !!this.drift().attestationDigest);
+
+  /** Computed: risk trend icon */
+  trendIcon = computed(() => {
+    const trend = this.summary().riskTrend;
+    switch (trend) {
+      case 'increasing':
+        return '↑';
+      case 'decreasing':
+        return '↓';
+      default:
+        return '→';
+    }
+  });
+
+  /** Computed: risk trend CSS class */
+  trendClass = computed(() => {
+    const trend = this.summary().riskTrend;
+    return `risk-drift-card__trend--${trend}`;
+  });
+
+  /** Computed: top drifted sinks to preview */
+  previewSinks = computed(() => {
+    const sinks = this.drift().driftedSinks;
+    const max = this.maxPreviewSinks();
+    // Sort by risk delta (highest first), then severity
+    return sinks
+      .slice()
+      .sort((a, b) => {
+        const severityOrder = { critical: 0, high: 1, medium: 2, low: 3, info: 4 };
+        const aSev = severityOrder[a.severity ?? 'info'];
+        const bSev = severityOrder[b.severity ?? 'info'];
+        if (aSev !== bSev) return aSev - bSev;
+        return b.riskDelta - a.riskDelta;
+      })
+      .slice(0, max);
+  });
+
+  /** Computed: additional sinks count */
+  additionalSinksCount = computed(() => {
+    return Math.max(0, this.drift().driftedSinks.length - this.maxPreviewSinks());
+  });
+
+  /** Handle view details click */
+  onViewDetails(): void {
+    this.viewDetails.emit();
+  }
+
+  /** Handle sink click */
+  onSinkClick(sink: DriftedSink): void {
+    this.sinkClick.emit(sink);
+  }
+
+  /** Format risk delta */
+  formatRiskDelta(delta: number): string {
+    if (delta > 0) return `+${delta}`;
+    return delta.toString();
+  }
+
+  /** Get severity badge class */
+  getSeverityClass(severity?: string): string {
+    return severity ? `risk-drift-card__severity--${severity}` : '';
+  }
+
+  /** Format timestamp */
+  formatTime(iso: string): string {
+    const date = new Date(iso);
+    return date.toLocaleString();
+  }
+
+  /** Get bucket label */
+  getBucketLabel(bucket: string | null): string {
+    if (!bucket) return 'N/A';
+    const labels: Record<string, string> = {
+      entrypoint: 'Entry Point',
+      direct: 'Direct',
+      runtime: 'Runtime',
+      unknown: 'Unknown',
+      unreachable: 'Unreachable'
+    };
+    return labels[bucket] ?? bucket;
+  }
+}