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src/Policy/StellaOps.Policy.Engine/EffectiveDecisionMap/MessagingEffectiveDecisionMap.cs

@@ -0,0 +1,428 @@
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Options;
+using StellaOps.Messaging;
+using StellaOps.Messaging.Abstractions;
+using StellaOps.Policy.Engine.Options;
+using StellaOps.Policy.Engine.Telemetry;
+
+namespace StellaOps.Policy.Engine.EffectiveDecisionMap;
+
+/// <summary>
+/// Transport-agnostic effective decision map using StellaOps.Messaging abstractions.
+/// Works with any configured transport (Valkey, PostgreSQL, InMemory).
+/// </summary>
+internal sealed class MessagingEffectiveDecisionMap : IEffectiveDecisionMap
+{
+    private readonly IDistributedCache<string, EffectiveDecisionEntry> _entryCache;
+    private readonly ISortedIndex<string, string> _assetIndex;
+    private readonly IDistributedCache<string, long> _versionCache;
+    private readonly ILogger<MessagingEffectiveDecisionMap> _logger;
+    private readonly EffectiveDecisionMapOptions _options;
+    private readonly TimeProvider _timeProvider;
+
+    private const string EntryKeyPrefix = "edm:entry";
+    private const string IndexKeyPrefix = "edm:index";
+    private const string VersionKeyPrefix = "edm:version";
+
+    public MessagingEffectiveDecisionMap(
+        IDistributedCacheFactory cacheFactory,
+        ISortedIndexFactory sortedIndexFactory,
+        ILogger<MessagingEffectiveDecisionMap> logger,
+        IOptions<PolicyEngineOptions> options,
+        TimeProvider timeProvider)
+    {
+        ArgumentNullException.ThrowIfNull(cacheFactory);
+        ArgumentNullException.ThrowIfNull(sortedIndexFactory);
+
+        _entryCache = cacheFactory.Create<string, EffectiveDecisionEntry>(new CacheOptions { KeyPrefix = "edm:entries" });
+        _assetIndex = sortedIndexFactory.Create<string, string>("edm-asset-index");
+        _versionCache = cacheFactory.Create<string, long>(new CacheOptions { KeyPrefix = "edm:versions" });
+        _logger = logger ?? throw new ArgumentNullException(nameof(logger));
+        _options = options?.Value.EffectiveDecisionMap ?? new EffectiveDecisionMapOptions();
+        _timeProvider = timeProvider ?? throw new ArgumentNullException(nameof(timeProvider));
+    }
+
+    public async Task SetAsync(
+        string tenantId,
+        string snapshotId,
+        EffectiveDecisionEntry entry,
+        CancellationToken cancellationToken = default)
+    {
+        ArgumentNullException.ThrowIfNull(entry);
+
+        var entryKey = GetEntryKey(tenantId, snapshotId, entry.AssetId);
+        var indexKey = GetIndexKey(tenantId, snapshotId);
+        var now = _timeProvider.GetUtcNow();
+
+        var ttl = entry.ExpiresAt - now;
+        if (ttl <= TimeSpan.Zero)
+        {
+            ttl = TimeSpan.FromMinutes(_options.DefaultTtlMinutes);
+        }
+
+        var cacheOptions = new CacheEntryOptions { TimeToLive = ttl };
+
+        // Store entry with TTL
+        await _entryCache.SetAsync(entryKey, entry, cacheOptions, cancellationToken).ConfigureAwait(false);
+
+        // Add to sorted index by evaluated_at timestamp
+        var score = entry.EvaluatedAt.ToUnixTimeMilliseconds();
+        await _assetIndex.AddAsync(indexKey, entry.AssetId, score, cancellationToken).ConfigureAwait(false);
+
+        // Set TTL on index (slightly longer than entries)
+        await _assetIndex.SetExpirationAsync(indexKey, ttl.Add(TimeSpan.FromMinutes(5)), cancellationToken).ConfigureAwait(false);
+
+        PolicyEngineTelemetry.EffectiveDecisionMapOperations.Add(1,
+            new KeyValuePair<string, object?>("operation", "set"),
+            new KeyValuePair<string, object?>("tenant_id", tenantId));
+    }
+
+    public async Task SetBatchAsync(
+        string tenantId,
+        string snapshotId,
+        IEnumerable<EffectiveDecisionEntry> entries,
+        CancellationToken cancellationToken = default)
+    {
+        var now = _timeProvider.GetUtcNow();
+        var indexKey = GetIndexKey(tenantId, snapshotId);
+        var count = 0;
+        var maxTtl = TimeSpan.Zero;
+
+        var indexElements = new List<ScoredElement<string>>();
+
+        foreach (var entry in entries)
+        {
+            var entryKey = GetEntryKey(tenantId, snapshotId, entry.AssetId);
+            var ttl = entry.ExpiresAt - now;
+            if (ttl <= TimeSpan.Zero)
+            {
+                ttl = TimeSpan.FromMinutes(_options.DefaultTtlMinutes);
+            }
+
+            if (ttl > maxTtl) maxTtl = ttl;
+
+            var cacheOptions = new CacheEntryOptions { TimeToLive = ttl };
+            await _entryCache.SetAsync(entryKey, entry, cacheOptions, cancellationToken).ConfigureAwait(false);
+
+            indexElements.Add(new ScoredElement<string>(entry.AssetId, entry.EvaluatedAt.ToUnixTimeMilliseconds()));
+            count++;
+        }
+
+        if (indexElements.Count > 0)
+        {
+            await _assetIndex.AddRangeAsync(indexKey, indexElements, cancellationToken).ConfigureAwait(false);
+            await _assetIndex.SetExpirationAsync(indexKey, maxTtl.Add(TimeSpan.FromMinutes(5)), cancellationToken).ConfigureAwait(false);
+        }
+
+        // Increment version after batch write
+        await IncrementVersionAsync(tenantId, snapshotId, cancellationToken).ConfigureAwait(false);
+
+        PolicyEngineTelemetry.EffectiveDecisionMapOperations.Add(count,
+            new KeyValuePair<string, object?>("operation", "set_batch"),
+            new KeyValuePair<string, object?>("tenant_id", tenantId));
+
+        _logger.LogDebug("Set {Count} effective decisions for snapshot {SnapshotId}", count, snapshotId);
+    }
+
+    public async Task<EffectiveDecisionEntry?> GetAsync(
+        string tenantId,
+        string snapshotId,
+        string assetId,
+        CancellationToken cancellationToken = default)
+    {
+        var entryKey = GetEntryKey(tenantId, snapshotId, assetId);
+        var result = await _entryCache.GetAsync(entryKey, cancellationToken).ConfigureAwait(false);
+
+        PolicyEngineTelemetry.EffectiveDecisionMapOperations.Add(1,
+            new KeyValuePair<string, object?>("operation", "get"),
+            new KeyValuePair<string, object?>("tenant_id", tenantId),
+            new KeyValuePair<string, object?>("cache_hit", result.HasValue));
+
+        return result.HasValue ? result.Value : null;
+    }
+
+    public async Task<EffectiveDecisionQueryResult> GetBatchAsync(
+        string tenantId,
+        string snapshotId,
+        IReadOnlyList<string> assetIds,
+        CancellationToken cancellationToken = default)
+    {
+        var entries = new Dictionary<string, EffectiveDecisionEntry>();
+        var notFound = new List<string>();
+
+        foreach (var assetId in assetIds)
+        {
+            var entryKey = GetEntryKey(tenantId, snapshotId, assetId);
+            var result = await _entryCache.GetAsync(entryKey, cancellationToken).ConfigureAwait(false);
+
+            if (result.HasValue && result.Value is not null)
+            {
+                entries[assetId] = result.Value;
+            }
+            else
+            {
+                notFound.Add(assetId);
+            }
+        }
+
+        var version = await GetVersionAsync(tenantId, snapshotId, cancellationToken).ConfigureAwait(false);
+
+        PolicyEngineTelemetry.EffectiveDecisionMapOperations.Add(assetIds.Count,
+            new KeyValuePair<string, object?>("operation", "get_batch"),
+            new KeyValuePair<string, object?>("tenant_id", tenantId));
+
+        return new EffectiveDecisionQueryResult
+        {
+            Entries = entries,
+            NotFound = notFound,
+            MapVersion = version,
+            FromCache = true,
+        };
+    }
+
+    public async Task<IReadOnlyList<EffectiveDecisionEntry>> GetAllForSnapshotAsync(
+        string tenantId,
+        string snapshotId,
+        EffectiveDecisionFilter? filter = null,
+        CancellationToken cancellationToken = default)
+    {
+        var indexKey = GetIndexKey(tenantId, snapshotId);
+
+        // Get all asset IDs from index, ordered by score (evaluated_at) descending
+        var assetElements = await _assetIndex.GetByRankAsync(
+            indexKey, 0, -1, SortOrder.Descending, cancellationToken).ConfigureAwait(false);
+
+        if (assetElements.Count == 0)
+        {
+            return Array.Empty<EffectiveDecisionEntry>();
+        }
+
+        var entries = new List<EffectiveDecisionEntry>();
+
+        foreach (var element in assetElements)
+        {
+            var entryKey = GetEntryKey(tenantId, snapshotId, element.Element);
+            var result = await _entryCache.GetAsync(entryKey, cancellationToken).ConfigureAwait(false);
+
+            if (!result.HasValue || result.Value is null) continue;
+
+            var entry = result.Value;
+
+            // Apply filters
+            if (filter != null)
+            {
+                if (filter.Statuses?.Count > 0 &&
+                    !filter.Statuses.Contains(entry.Status, StringComparer.OrdinalIgnoreCase))
+                {
+                    continue;
+                }
+
+                if (filter.Severities?.Count > 0 &&
+                    (entry.Severity is null || !filter.Severities.Contains(entry.Severity, StringComparer.OrdinalIgnoreCase)))
+                {
+                    continue;
+                }
+
+                if (filter.HasException == true && entry.ExceptionId is null)
+                {
+                    continue;
+                }
+
+                if (filter.HasException == false && entry.ExceptionId is not null)
+                {
+                    continue;
+                }
+
+                if (filter.MinAdvisoryCount.HasValue && entry.AdvisoryCount < filter.MinAdvisoryCount)
+                {
+                    continue;
+                }
+
+                if (filter.MinHighSeverityCount.HasValue && entry.HighSeverityCount < filter.MinHighSeverityCount)
+                {
+                    continue;
+                }
+            }
+
+            entries.Add(entry);
+
+            // Apply limit (accounting for offset)
+            if (filter?.Limit > 0 && entries.Count >= filter.Limit + (filter?.Offset ?? 0))
+            {
+                break;
+            }
+        }
+
+        // Apply offset
+        if (filter?.Offset > 0)
+        {
+            entries = entries.Skip(filter.Offset).ToList();
+        }
+
+        // Apply final limit
+        if (filter?.Limit > 0)
+        {
+            entries = entries.Take(filter.Limit).ToList();
+        }
+
+        PolicyEngineTelemetry.EffectiveDecisionMapOperations.Add(1,
+            new KeyValuePair<string, object?>("operation", "get_all"),
+            new KeyValuePair<string, object?>("tenant_id", tenantId));
+
+        return entries;
+    }
+
+    public async Task<EffectiveDecisionSummary> GetSummaryAsync(
+        string tenantId,
+        string snapshotId,
+        CancellationToken cancellationToken = default)
+    {
+        var entries = await GetAllForSnapshotAsync(tenantId, snapshotId, null, cancellationToken)
+            .ConfigureAwait(false);
+
+        var statusCounts = entries
+            .GroupBy(e => e.Status, StringComparer.OrdinalIgnoreCase)
+            .ToDictionary(g => g.Key, g => g.Count(), StringComparer.OrdinalIgnoreCase);
+
+        var severityCounts = entries
+            .Where(e => e.Severity is not null)
+            .GroupBy(e => e.Severity!, StringComparer.OrdinalIgnoreCase)
+            .ToDictionary(g => g.Key, g => g.Count(), StringComparer.OrdinalIgnoreCase);
+
+        var version = await GetVersionAsync(tenantId, snapshotId, cancellationToken).ConfigureAwait(false);
+
+        return new EffectiveDecisionSummary
+        {
+            SnapshotId = snapshotId,
+            TotalAssets = entries.Count,
+            StatusCounts = statusCounts,
+            SeverityCounts = severityCounts,
+            ExceptionCount = entries.Count(e => e.ExceptionId is not null),
+            MapVersion = version,
+            ComputedAt = _timeProvider.GetUtcNow(),
+        };
+    }
+
+    public async Task InvalidateAsync(
+        string tenantId,
+        string snapshotId,
+        string assetId,
+        CancellationToken cancellationToken = default)
+    {
+        var entryKey = GetEntryKey(tenantId, snapshotId, assetId);
+        var indexKey = GetIndexKey(tenantId, snapshotId);
+
+        await _entryCache.InvalidateAsync(entryKey, cancellationToken).ConfigureAwait(false);
+        await _assetIndex.RemoveAsync(indexKey, assetId, cancellationToken).ConfigureAwait(false);
+
+        await IncrementVersionAsync(tenantId, snapshotId, cancellationToken).ConfigureAwait(false);
+
+        PolicyEngineTelemetry.EffectiveDecisionMapOperations.Add(1,
+            new KeyValuePair<string, object?>("operation", "invalidate"),
+            new KeyValuePair<string, object?>("tenant_id", tenantId));
+    }
+
+    public async Task InvalidateSnapshotAsync(
+        string tenantId,
+        string snapshotId,
+        CancellationToken cancellationToken = default)
+    {
+        var indexKey = GetIndexKey(tenantId, snapshotId);
+
+        // Get all asset IDs from the index
+        var assetElements = await _assetIndex.GetByRankAsync(indexKey, 0, -1, cancellationToken: cancellationToken).ConfigureAwait(false);
+        var count = assetElements.Count;
+
+        foreach (var element in assetElements)
+        {
+            var entryKey = GetEntryKey(tenantId, snapshotId, element.Element);
+            await _entryCache.InvalidateAsync(entryKey, cancellationToken).ConfigureAwait(false);
+        }
+
+        // Delete the index
+        await _assetIndex.DeleteAsync(indexKey, cancellationToken).ConfigureAwait(false);
+
+        // Delete the version
+        var versionKey = GetVersionKey(tenantId, snapshotId);
+        await _versionCache.InvalidateAsync(versionKey, cancellationToken).ConfigureAwait(false);
+
+        PolicyEngineTelemetry.EffectiveDecisionMapOperations.Add(count,
+            new KeyValuePair<string, object?>("operation", "invalidate_snapshot"),
+            new KeyValuePair<string, object?>("tenant_id", tenantId));
+
+        _logger.LogInformation("Invalidated {Count} entries for snapshot {SnapshotId}", count, snapshotId);
+    }
+
+    public async Task InvalidateTenantAsync(
+        string tenantId,
+        CancellationToken cancellationToken = default)
+    {
+        // Invalidate all entries and indexes for the tenant using pattern matching
+        var pattern = $"{EntryKeyPrefix}:{tenantId}:*";
+        var entryCount = await _entryCache.InvalidateByPatternAsync(pattern, cancellationToken).ConfigureAwait(false);
+
+        // Note: ISortedIndex doesn't have pattern-based deletion, so we can't easily clean up indexes
+        // This is a limitation of the abstraction - the Redis implementation handled this with KEYS scan
+
+        PolicyEngineTelemetry.EffectiveDecisionMapOperations.Add(entryCount,
+            new KeyValuePair<string, object?>("operation", "invalidate_tenant"),
+            new KeyValuePair<string, object?>("tenant_id", tenantId));
+
+        _logger.LogInformation("Invalidated {Count} entries for tenant {TenantId}", entryCount, tenantId);
+    }
+
+    public async Task<long> GetVersionAsync(
+        string tenantId,
+        string snapshotId,
+        CancellationToken cancellationToken = default)
+    {
+        var versionKey = GetVersionKey(tenantId, snapshotId);
+        var result = await _versionCache.GetAsync(versionKey, cancellationToken).ConfigureAwait(false);
+        return result.HasValue ? result.Value : 0;
+    }
+
+    public async Task<long> IncrementVersionAsync(
+        string tenantId,
+        string snapshotId,
+        CancellationToken cancellationToken = default)
+    {
+        var versionKey = GetVersionKey(tenantId, snapshotId);
+        var current = await GetVersionAsync(tenantId, snapshotId, cancellationToken).ConfigureAwait(false);
+        var newVersion = current + 1;
+
+        var cacheOptions = new CacheEntryOptions
+        {
+            TimeToLive = TimeSpan.FromMinutes(_options.DefaultTtlMinutes + 10)
+        };
+
+        await _versionCache.SetAsync(versionKey, newVersion, cacheOptions, cancellationToken).ConfigureAwait(false);
+
+        return newVersion;
+    }
+
+    public Task<EffectiveDecisionMapStats> GetStatsAsync(
+        string? tenantId = null,
+        CancellationToken cancellationToken = default)
+    {
+        // Stats require implementation-specific queries that aren't available through abstractions
+        // Return placeholder stats - a complete implementation would need transport-specific code
+        return Task.FromResult(new EffectiveDecisionMapStats
+        {
+            TotalEntries = 0,
+            TotalSnapshots = 0,
+            MemoryUsedBytes = null,
+            ExpiringWithinHour = 0,
+            LastEvictionAt = null,
+            LastEvictionCount = 0,
+        });
+    }
+
+    private static string GetEntryKey(string tenantId, string snapshotId, string assetId) =>
+        $"{EntryKeyPrefix}:{tenantId}:{snapshotId}:{assetId}";
+
+    private static string GetIndexKey(string tenantId, string snapshotId) =>
+        $"{IndexKeyPrefix}:{tenantId}:{snapshotId}";
+
+    private static string GetVersionKey(string tenantId, string snapshotId) =>
+        $"{VersionKeyPrefix}:{tenantId}:{snapshotId}";
+}

src/Policy/StellaOps.Policy.Engine/ExceptionCache/MessagingExceptionEffectiveCache.cs

@@ -0,0 +1,584 @@
+using System.Collections.Immutable;
+using System.Diagnostics;
+using System.Text.Json;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Options;
+using StellaOps.Messaging;
+using StellaOps.Messaging.Abstractions;
+using StellaOps.Policy.Engine.Options;
+using StellaOps.Policy.Engine.Telemetry;
+using StellaOps.Policy.Storage.Postgres.Models;
+using StellaOps.Policy.Storage.Postgres.Repositories;
+
+namespace StellaOps.Policy.Engine.ExceptionCache;
+
+/// <summary>
+/// Transport-agnostic exception effective cache using StellaOps.Messaging abstractions.
+/// Works with any configured transport (Valkey, PostgreSQL, InMemory).
+/// </summary>
+internal sealed class MessagingExceptionEffectiveCache : IExceptionEffectiveCache
+{
+    private readonly IDistributedCache<string, List<ExceptionCacheEntry>> _entryCache;
+    private readonly ISetStore<string, string> _exceptionIndex;
+    private readonly IDistributedCache<string, long> _versionCache;
+    private readonly IDistributedCache<string, Dictionary<string, string>> _statsCache;
+    private readonly IExceptionRepository _repository;
+    private readonly ILogger<MessagingExceptionEffectiveCache> _logger;
+    private readonly ExceptionCacheOptions _options;
+    private readonly TimeProvider _timeProvider;
+
+    private const string EntryKeyPrefix = "exc:entry";
+    private const string IndexKeyPrefix = "exc:index";
+    private const string VersionKeyPrefix = "exc:version";
+    private const string StatsKeyPrefix = "exc:stats";
+
+    public MessagingExceptionEffectiveCache(
+        IDistributedCacheFactory cacheFactory,
+        ISetStoreFactory setStoreFactory,
+        IExceptionRepository repository,
+        ILogger<MessagingExceptionEffectiveCache> logger,
+        IOptions<PolicyEngineOptions> options,
+        TimeProvider timeProvider)
+    {
+        ArgumentNullException.ThrowIfNull(cacheFactory);
+        ArgumentNullException.ThrowIfNull(setStoreFactory);
+
+        _entryCache = cacheFactory.Create<string, List<ExceptionCacheEntry>>(new CacheOptions { KeyPrefix = EntryKeyPrefix });
+        _exceptionIndex = setStoreFactory.Create<string, string>("exc-exception-index");
+        _versionCache = cacheFactory.Create<string, long>(new CacheOptions { KeyPrefix = VersionKeyPrefix });
+        _statsCache = cacheFactory.Create<string, Dictionary<string, string>>(new CacheOptions { KeyPrefix = StatsKeyPrefix });
+        _repository = repository ?? throw new ArgumentNullException(nameof(repository));
+        _logger = logger ?? throw new ArgumentNullException(nameof(logger));
+        _options = options?.Value.ExceptionCache ?? new ExceptionCacheOptions();
+        _timeProvider = timeProvider ?? throw new ArgumentNullException(nameof(timeProvider));
+    }
+
+    public async Task<ExceptionCacheQueryResult> GetForAssetAsync(
+        string tenantId,
+        string assetId,
+        string? advisoryId,
+        DateTimeOffset asOf,
+        CancellationToken cancellationToken = default)
+    {
+        var sw = Stopwatch.StartNew();
+        var entries = new List<ExceptionCacheEntry>();
+        var fromCache = false;
+
+        // Try specific advisory key first
+        if (advisoryId is not null)
+        {
+            var specificKey = GetAssetKey(tenantId, assetId, advisoryId);
+            var specificResult = await _entryCache.GetAsync(specificKey, cancellationToken).ConfigureAwait(false);
+            if (specificResult.HasValue && specificResult.Value is not null)
+            {
+                entries.AddRange(specificResult.Value);
+                fromCache = true;
+            }
+        }
+
+        // Also get "all" entries (exceptions without specific advisory)
+        var allKey = GetAssetKey(tenantId, assetId, null);
+        var allResult = await _entryCache.GetAsync(allKey, cancellationToken).ConfigureAwait(false);
+        if (allResult.HasValue && allResult.Value is not null)
+        {
+            entries.AddRange(allResult.Value);
+            fromCache = true;
+        }
+
+        // Filter by time and sort by priority
+        var validEntries = entries
+            .Where(e => e.EffectiveFrom <= asOf && (e.ExpiresAt is null || e.ExpiresAt > asOf))
+            .OrderByDescending(e => e.Priority)
+            .ToImmutableArray();
+
+        var version = await GetVersionAsync(tenantId, cancellationToken).ConfigureAwait(false);
+
+        sw.Stop();
+
+        PolicyEngineTelemetry.RecordExceptionCacheOperation(tenantId, fromCache ? "hit" : "miss");
+
+        return new ExceptionCacheQueryResult
+        {
+            Entries = validEntries,
+            FromCache = fromCache,
+            CacheVersion = version,
+            QueryDurationMs = sw.ElapsedMilliseconds,
+        };
+    }
+
+    public async Task<IReadOnlyDictionary<string, ExceptionCacheQueryResult>> GetBatchAsync(
+        string tenantId,
+        IReadOnlyList<string> assetIds,
+        DateTimeOffset asOf,
+        CancellationToken cancellationToken = default)
+    {
+        var results = new Dictionary<string, ExceptionCacheQueryResult>(StringComparer.OrdinalIgnoreCase);
+        var version = await GetVersionAsync(tenantId, cancellationToken).ConfigureAwait(false);
+
+        foreach (var assetId in assetIds)
+        {
+            var entries = ImmutableArray<ExceptionCacheEntry>.Empty;
+            var fromCache = false;
+
+            var allKey = GetAssetKey(tenantId, assetId, null);
+            var result = await _entryCache.GetAsync(allKey, cancellationToken).ConfigureAwait(false);
+
+            if (result.HasValue && result.Value is not null)
+            {
+                entries = result.Value
+                    .Where(e => e.EffectiveFrom <= asOf && (e.ExpiresAt is null || e.ExpiresAt > asOf))
+                    .OrderByDescending(e => e.Priority)
+                    .ToImmutableArray();
+                fromCache = true;
+            }
+
+            results[assetId] = new ExceptionCacheQueryResult
+            {
+                Entries = entries,
+                FromCache = fromCache,
+                CacheVersion = version,
+                QueryDurationMs = 0,
+            };
+        }
+
+        PolicyEngineTelemetry.RecordExceptionCacheOperation(tenantId, "batch_get");
+
+        return results;
+    }
+
+    public async Task SetAsync(
+        string tenantId,
+        ExceptionCacheEntry entry,
+        CancellationToken cancellationToken = default)
+    {
+        ArgumentNullException.ThrowIfNull(entry);
+
+        var assetKey = GetAssetKey(tenantId, entry.AssetId, entry.AdvisoryId);
+        var exceptionIndexKey = GetExceptionIndexKey(tenantId, entry.ExceptionId);
+
+        // Get existing entries for this asset
+        var existingResult = await _entryCache.GetAsync(assetKey, cancellationToken).ConfigureAwait(false);
+        var entries = existingResult.HasValue && existingResult.Value is not null
+            ? existingResult.Value
+            : new List<ExceptionCacheEntry>();
+
+        // Remove existing entry for same exception if any
+        entries.RemoveAll(e => e.ExceptionId == entry.ExceptionId);
+
+        // Add new entry
+        entries.Add(entry);
+
+        var ttl = ComputeTtl(entry);
+        var cacheOptions = new CacheEntryOptions { TimeToLive = ttl };
+
+        // Store entry
+        await _entryCache.SetAsync(assetKey, entries, cacheOptions, cancellationToken).ConfigureAwait(false);
+
+        // Update exception index
+        await _exceptionIndex.AddAsync(exceptionIndexKey, assetKey, cancellationToken).ConfigureAwait(false);
+        await _exceptionIndex.SetExpirationAsync(exceptionIndexKey, ttl.Add(TimeSpan.FromMinutes(5)), cancellationToken)
+            .ConfigureAwait(false);
+
+        PolicyEngineTelemetry.RecordExceptionCacheOperation(tenantId, "set");
+    }
+
+    public async Task SetBatchAsync(
+        string tenantId,
+        IEnumerable<ExceptionCacheEntry> entries,
+        CancellationToken cancellationToken = default)
+    {
+        var count = 0;
+
+        // Group entries by asset+advisory
+        var groupedEntries = entries
+            .GroupBy(e => GetAssetKey(tenantId, e.AssetId, e.AdvisoryId))
+            .ToDictionary(g => g.Key, g => g.ToList());
+
+        foreach (var (assetKey, assetEntries) in groupedEntries)
+        {
+            var ttl = assetEntries.Max(ComputeTtl);
+            var cacheOptions = new CacheEntryOptions { TimeToLive = ttl };
+
+            await _entryCache.SetAsync(assetKey, assetEntries, cacheOptions, cancellationToken).ConfigureAwait(false);
+
+            // Update exception indexes
+            foreach (var entry in assetEntries)
+            {
+                var exceptionIndexKey = GetExceptionIndexKey(tenantId, entry.ExceptionId);
+                await _exceptionIndex.AddAsync(exceptionIndexKey, assetKey, cancellationToken).ConfigureAwait(false);
+                await _exceptionIndex.SetExpirationAsync(exceptionIndexKey, ttl.Add(TimeSpan.FromMinutes(5)), cancellationToken)
+                    .ConfigureAwait(false);
+            }
+
+            count += assetEntries.Count;
+        }
+
+        // Increment version
+        await IncrementVersionAsync(tenantId, cancellationToken).ConfigureAwait(false);
+
+        PolicyEngineTelemetry.RecordExceptionCacheOperation(tenantId, "set_batch");
+
+        _logger.LogDebug("Set {Count} exception cache entries for tenant {TenantId}", count, tenantId);
+    }
+
+    public async Task InvalidateExceptionAsync(
+        string tenantId,
+        string exceptionId,
+        CancellationToken cancellationToken = default)
+    {
+        var exceptionIndexKey = GetExceptionIndexKey(tenantId, exceptionId);
+
+        // Get all asset keys affected by this exception
+        var assetKeys = await _exceptionIndex.GetMembersAsync(exceptionIndexKey, cancellationToken).ConfigureAwait(false);
+
+        if (assetKeys.Count > 0)
+        {
+            // For each asset key, remove entries for this exception
+            foreach (var assetKey in assetKeys)
+            {
+                var result = await _entryCache.GetAsync(assetKey, cancellationToken).ConfigureAwait(false);
+                if (result.HasValue && result.Value is not null)
+                {
+                    var entries = result.Value;
+                    entries.RemoveAll(e => e.ExceptionId == exceptionId);
+
+                    if (entries.Count > 0)
+                    {
+                        var cacheOptions = new CacheEntryOptions
+                        {
+                            TimeToLive = TimeSpan.FromMinutes(_options.DefaultTtlMinutes)
+                        };
+                        await _entryCache.SetAsync(assetKey, entries, cacheOptions, cancellationToken).ConfigureAwait(false);
+                    }
+                    else
+                    {
+                        await _entryCache.InvalidateAsync(assetKey, cancellationToken).ConfigureAwait(false);
+                    }
+                }
+            }
+        }
+
+        // Delete the exception index
+        await _exceptionIndex.DeleteAsync(exceptionIndexKey, cancellationToken).ConfigureAwait(false);
+
+        // Increment version
+        await IncrementVersionAsync(tenantId, cancellationToken).ConfigureAwait(false);
+
+        PolicyEngineTelemetry.RecordExceptionCacheOperation(tenantId, "invalidate_exception");
+
+        _logger.LogInformation(
+            "Invalidated exception {ExceptionId} affecting {Count} assets for tenant {TenantId}",
+            exceptionId, assetKeys.Count, tenantId);
+    }
+
+    public async Task InvalidateAssetAsync(
+        string tenantId,
+        string assetId,
+        CancellationToken cancellationToken = default)
+    {
+        // Invalidate all keys for this asset using pattern
+        var pattern = $"{EntryKeyPrefix}:{tenantId}:{assetId}:*";
+        var count = await _entryCache.InvalidateByPatternAsync(pattern, cancellationToken).ConfigureAwait(false);
+
+        // Increment version
+        await IncrementVersionAsync(tenantId, cancellationToken).ConfigureAwait(false);
+
+        PolicyEngineTelemetry.RecordExceptionCacheOperation(tenantId, "invalidate_asset");
+
+        _logger.LogDebug("Invalidated {Count} cache keys for asset {AssetId}", count, assetId);
+    }
+
+    public async Task InvalidateTenantAsync(
+        string tenantId,
+        CancellationToken cancellationToken = default)
+    {
+        // Invalidate all entry keys for tenant
+        var entryPattern = $"{EntryKeyPrefix}:{tenantId}:*";
+        var entryCount = await _entryCache.InvalidateByPatternAsync(entryPattern, cancellationToken).ConfigureAwait(false);
+
+        // Invalidate version and stats
+        var versionKey = GetVersionKey(tenantId);
+        await _versionCache.InvalidateAsync(versionKey, cancellationToken).ConfigureAwait(false);
+
+        var statsKey = GetStatsKey(tenantId);
+        await _statsCache.InvalidateAsync(statsKey, cancellationToken).ConfigureAwait(false);
+
+        PolicyEngineTelemetry.RecordExceptionCacheOperation(tenantId, "invalidate_tenant");
+
+        _logger.LogInformation("Invalidated {Count} cache keys for tenant {TenantId}", entryCount, tenantId);
+    }
+
+    public async Task WarmAsync(
+        string tenantId,
+        CancellationToken cancellationToken = default)
+    {
+        using var activity = PolicyEngineTelemetry.ActivitySource.StartActivity(
+            "exception.cache.warm", ActivityKind.Internal);
+        activity?.SetTag("tenant_id", tenantId);
+
+        var sw = Stopwatch.StartNew();
+        var now = _timeProvider.GetUtcNow();
+
+        _logger.LogInformation("Starting cache warm for tenant {TenantId}", tenantId);
+
+        try
+        {
+            var exceptions = await _repository.GetAllAsync(
+                tenantId,
+                ExceptionStatus.Active,
+                limit: _options.MaxEntriesPerTenant,
+                offset: 0,
+                cancellationToken: cancellationToken).ConfigureAwait(false);
+
+            if (exceptions.Count == 0)
+            {
+                _logger.LogDebug("No active exceptions to warm for tenant {TenantId}", tenantId);
+                return;
+            }
+
+            var entries = new List<ExceptionCacheEntry>();
+
+            foreach (var exception in exceptions)
+            {
+                entries.Add(new ExceptionCacheEntry
+                {
+                    ExceptionId = exception.Id.ToString(),
+                    AssetId = string.IsNullOrWhiteSpace(exception.ProjectId) ? "*" : exception.ProjectId!,
+                    AdvisoryId = null,
+                    CveId = null,
+                    DecisionOverride = "allow",
+                    ExceptionType = "waiver",
+                    Priority = 0,
+                    EffectiveFrom = exception.CreatedAt,
+                    ExpiresAt = exception.ExpiresAt,
+                    CachedAt = now,
+                    ExceptionName = exception.Name,
+                });
+            }
+
+            if (entries.Count > 0)
+            {
+                await SetBatchAsync(tenantId, entries, cancellationToken).ConfigureAwait(false);
+            }
+
+            sw.Stop();
+
+            // Update warm stats
+            await UpdateWarmStatsAsync(tenantId, now, entries.Count, cancellationToken).ConfigureAwait(false);
+
+            PolicyEngineTelemetry.RecordExceptionCacheOperation(tenantId, "warm");
+
+            _logger.LogInformation(
+                "Warmed cache with {Count} entries from {ExceptionCount} exceptions for tenant {TenantId} in {Duration}ms",
+                entries.Count, exceptions.Count, tenantId, sw.ElapsedMilliseconds);
+        }
+        catch (Exception ex)
+        {
+            _logger.LogError(ex, "Failed to warm cache for tenant {TenantId}", tenantId);
+            PolicyEngineTelemetry.RecordError("exception_cache_warm", tenantId);
+            throw;
+        }
+    }
+
+    public async Task<ExceptionCacheSummary> GetSummaryAsync(
+        string tenantId,
+        CancellationToken cancellationToken = default)
+    {
+        var now = _timeProvider.GetUtcNow();
+
+        // Note: Full summary requires scanning keys which isn't efficient with abstractions
+        // Return placeholder data - complete implementation would need transport-specific code
+        var version = await GetVersionAsync(tenantId, cancellationToken).ConfigureAwait(false);
+
+        return new ExceptionCacheSummary
+        {
+            TenantId = tenantId,
+            TotalEntries = 0,
+            UniqueExceptions = 0,
+            UniqueAssets = 0,
+            ByType = new Dictionary<string, int>(),
+            ByDecision = new Dictionary<string, int>(),
+            ExpiringWithinHour = 0,
+            CacheVersion = version,
+            ComputedAt = now,
+        };
+    }
+
+    public Task<ExceptionCacheStats> GetStatsAsync(
+        string? tenantId = null,
+        CancellationToken cancellationToken = default)
+    {
+        // Stats require implementation-specific queries that aren't available through abstractions
+        // Return placeholder stats - a complete implementation would need transport-specific code
+        return Task.FromResult(new ExceptionCacheStats
+        {
+            TotalEntries = 0,
+            TotalTenants = 0,
+            MemoryUsedBytes = null,
+            HitCount = 0,
+            MissCount = 0,
+            LastWarmAt = null,
+            LastInvalidationAt = null,
+        });
+    }
+
+    public async Task<long> GetVersionAsync(
+        string tenantId,
+        CancellationToken cancellationToken = default)
+    {
+        var versionKey = GetVersionKey(tenantId);
+        var result = await _versionCache.GetAsync(versionKey, cancellationToken).ConfigureAwait(false);
+        return result.HasValue ? result.Value : 0;
+    }
+
+    public async Task HandleExceptionEventAsync(
+        ExceptionEvent exceptionEvent,
+        CancellationToken cancellationToken = default)
+    {
+        ArgumentNullException.ThrowIfNull(exceptionEvent);
+
+        using var activity = PolicyEngineTelemetry.ActivitySource.StartActivity(
+            "exception.cache.handle_event", ActivityKind.Internal);
+        activity?.SetTag("tenant_id", exceptionEvent.TenantId);
+        activity?.SetTag("event_type", exceptionEvent.EventType);
+        activity?.SetTag("exception_id", exceptionEvent.ExceptionId);
+
+        _logger.LogDebug(
+            "Handling exception event {EventType} for exception {ExceptionId} tenant {TenantId}",
+            exceptionEvent.EventType, exceptionEvent.ExceptionId, exceptionEvent.TenantId);
+
+        switch (exceptionEvent.EventType.ToLowerInvariant())
+        {
+            case "activated":
+                await WarmExceptionAsync(exceptionEvent.TenantId, exceptionEvent.ExceptionId, cancellationToken)
+                    .ConfigureAwait(false);
+                break;
+
+            case "expired":
+            case "revoked":
+            case "deleted":
+                await InvalidateExceptionAsync(exceptionEvent.TenantId, exceptionEvent.ExceptionId, cancellationToken)
+                    .ConfigureAwait(false);
+                break;
+
+            case "updated":
+                await InvalidateExceptionAsync(exceptionEvent.TenantId, exceptionEvent.ExceptionId, cancellationToken)
+                    .ConfigureAwait(false);
+                await WarmExceptionAsync(exceptionEvent.TenantId, exceptionEvent.ExceptionId, cancellationToken)
+                    .ConfigureAwait(false);
+                break;
+
+            case "created":
+                await WarmExceptionAsync(exceptionEvent.TenantId, exceptionEvent.ExceptionId, cancellationToken)
+                    .ConfigureAwait(false);
+                break;
+
+            default:
+                _logger.LogWarning("Unknown exception event type: {EventType}", exceptionEvent.EventType);
+                break;
+        }
+
+        PolicyEngineTelemetry.RecordExceptionCacheOperation(exceptionEvent.TenantId, $"event_{exceptionEvent.EventType}");
+    }
+
+    private async Task WarmExceptionAsync(string tenantId, string exceptionId, CancellationToken cancellationToken)
+    {
+        if (!Guid.TryParse(exceptionId, out var exceptionGuid))
+        {
+            _logger.LogWarning("Unable to parse exception id {ExceptionId} for tenant {TenantId}", exceptionId, tenantId);
+            return;
+        }
+
+        var exception = await _repository.GetByIdAsync(tenantId, exceptionGuid, cancellationToken)
+            .ConfigureAwait(false);
+
+        if (exception is null || exception.Status != ExceptionStatus.Active)
+        {
+            return;
+        }
+
+        var now = _timeProvider.GetUtcNow();
+        var entries = new List<ExceptionCacheEntry>
+        {
+            new ExceptionCacheEntry
+            {
+                ExceptionId = exception.Id.ToString(),
+                AssetId = string.IsNullOrWhiteSpace(exception.ProjectId) ? "*" : exception.ProjectId!,
+                AdvisoryId = null,
+                CveId = null,
+                DecisionOverride = "allow",
+                ExceptionType = "waiver",
+                Priority = 0,
+                EffectiveFrom = exception.CreatedAt,
+                ExpiresAt = exception.ExpiresAt,
+                CachedAt = now,
+                ExceptionName = exception.Name,
+            }
+        };
+
+        await SetBatchAsync(tenantId, entries, cancellationToken).ConfigureAwait(false);
+
+        _logger.LogDebug(
+            "Warmed cache with {Count} entries for exception {ExceptionId}",
+            entries.Count, exceptionId);
+    }
+
+    private async Task<long> IncrementVersionAsync(string tenantId, CancellationToken cancellationToken)
+    {
+        var versionKey = GetVersionKey(tenantId);
+        var current = await GetVersionAsync(tenantId, cancellationToken).ConfigureAwait(false);
+        var newVersion = current + 1;
+
+        var cacheOptions = new CacheEntryOptions
+        {
+            TimeToLive = TimeSpan.FromMinutes(_options.DefaultTtlMinutes + 10)
+        };
+
+        await _versionCache.SetAsync(versionKey, newVersion, cacheOptions, cancellationToken).ConfigureAwait(false);
+
+        return newVersion;
+    }
+
+    private async Task UpdateWarmStatsAsync(string tenantId, DateTimeOffset warmAt, int count, CancellationToken cancellationToken)
+    {
+        var statsKey = GetStatsKey(tenantId);
+        var stats = new Dictionary<string, string>
+        {
+            ["lastWarmAt"] = warmAt.ToString("O"),
+            ["lastWarmCount"] = count.ToString(),
+        };
+
+        var cacheOptions = new CacheEntryOptions
+        {
+            TimeToLive = TimeSpan.FromMinutes(_options.DefaultTtlMinutes + 30)
+        };
+
+        await _statsCache.SetAsync(statsKey, stats, cacheOptions, cancellationToken).ConfigureAwait(false);
+    }
+
+    private TimeSpan ComputeTtl(ExceptionCacheEntry entry)
+    {
+        if (entry.ExpiresAt.HasValue)
+        {
+            var ttl = entry.ExpiresAt.Value - _timeProvider.GetUtcNow();
+            if (ttl > TimeSpan.Zero)
+            {
+                return ttl;
+            }
+        }
+
+        return TimeSpan.FromMinutes(_options.DefaultTtlMinutes);
+    }
+
+    private static string GetAssetKey(string tenantId, string assetId, string? advisoryId) =>
+        $"{tenantId}:{assetId}:{advisoryId ?? "all"}";
+
+    private static string GetExceptionIndexKey(string tenantId, string exceptionId) =>
+        $"{tenantId}:idx:{exceptionId}";
+
+    private static string GetVersionKey(string tenantId) =>
+        $"{tenantId}";
+
+    private static string GetStatsKey(string tenantId) =>
+        $"{tenantId}";
+}

src/Policy/StellaOps.Policy.Engine/Gates/PolicyGateDecision.cs

@@ -0,0 +1,332 @@
+using System.Collections.Immutable;
+using System.Text.Json.Serialization;
+
+namespace StellaOps.Policy.Engine.Gates;
+
+/// <summary>
+/// Result of a policy gate evaluation.
+/// </summary>
+public sealed record PolicyGateDecision
+{
+    /// <summary>
+    /// Unique identifier for this gate decision.
+    /// </summary>
+    [JsonPropertyName("gateId")]
+    public required string GateId { get; init; }
+
+    /// <summary>
+    /// The VEX status that was requested.
+    /// </summary>
+    [JsonPropertyName("requestedStatus")]
+    public required string RequestedStatus { get; init; }
+
+    /// <summary>
+    /// Subject of the decision (vuln, purl, symbol).
+    /// </summary>
+    [JsonPropertyName("subject")]
+    public required PolicyGateSubject Subject { get; init; }
+
+    /// <summary>
+    /// Evidence used in the decision.
+    /// </summary>
+    [JsonPropertyName("evidence")]
+    public required PolicyGateEvidence Evidence { get; init; }
+
+    /// <summary>
+    /// Individual gate results.
+    /// </summary>
+    [JsonPropertyName("gates")]
+    public required ImmutableArray<PolicyGateResult> Gates { get; init; }
+
+    /// <summary>
+    /// Overall decision (allow, block, warn).
+    /// </summary>
+    [JsonPropertyName("decision")]
+    public required PolicyGateDecisionType Decision { get; init; }
+
+    /// <summary>
+    /// Advisory message if decision includes warnings.
+    /// </summary>
+    [JsonPropertyName("advisory")]
+    public string? Advisory { get; init; }
+
+    /// <summary>
+    /// Name of the gate that blocked, if blocked.
+    /// </summary>
+    [JsonPropertyName("blockedBy")]
+    public string? BlockedBy { get; init; }
+
+    /// <summary>
+    /// Reason for blocking.
+    /// </summary>
+    [JsonPropertyName("blockReason")]
+    public string? BlockReason { get; init; }
+
+    /// <summary>
+    /// Suggestion for resolving a block.
+    /// </summary>
+    [JsonPropertyName("suggestion")]
+    public string? Suggestion { get; init; }
+
+    /// <summary>
+    /// Timestamp when the decision was made.
+    /// </summary>
+    [JsonPropertyName("decidedAt")]
+    public required DateTimeOffset DecidedAt { get; init; }
+}
+
+/// <summary>
+/// Subject of a policy gate decision.
+/// </summary>
+public sealed record PolicyGateSubject
+{
+    /// <summary>
+    /// Vulnerability identifier.
+    /// </summary>
+    [JsonPropertyName("vulnId")]
+    public string? VulnId { get; init; }
+
+    /// <summary>
+    /// Package URL.
+    /// </summary>
+    [JsonPropertyName("purl")]
+    public string? Purl { get; init; }
+
+    /// <summary>
+    /// Symbol identifier.
+    /// </summary>
+    [JsonPropertyName("symbolId")]
+    public string? SymbolId { get; init; }
+
+    /// <summary>
+    /// Scan identifier.
+    /// </summary>
+    [JsonPropertyName("scanId")]
+    public string? ScanId { get; init; }
+}
+
+/// <summary>
+/// Evidence used in a policy gate decision.
+/// </summary>
+public sealed record PolicyGateEvidence
+{
+    /// <summary>
+    /// v1 lattice state code (U, SR, SU, RO, RU, CR, CU, X).
+    /// </summary>
+    [JsonPropertyName("latticeState")]
+    public string? LatticeState { get; init; }
+
+    /// <summary>
+    /// Uncertainty tier (T1, T2, T3, T4).
+    /// </summary>
+    [JsonPropertyName("uncertaintyTier")]
+    public string? UncertaintyTier { get; init; }
+
+    /// <summary>
+    /// BLAKE3 hash of the callgraph.
+    /// </summary>
+    [JsonPropertyName("graphHash")]
+    public string? GraphHash { get; init; }
+
+    /// <summary>
+    /// Risk score incorporating uncertainty.
+    /// </summary>
+    [JsonPropertyName("riskScore")]
+    public double? RiskScore { get; init; }
+
+    /// <summary>
+    /// Reachability confidence (0-1).
+    /// </summary>
+    [JsonPropertyName("confidence")]
+    public double? Confidence { get; init; }
+
+    /// <summary>
+    /// Whether runtime evidence exists.
+    /// </summary>
+    [JsonPropertyName("hasRuntimeEvidence")]
+    public bool HasRuntimeEvidence { get; init; }
+
+    /// <summary>
+    /// Path length from entry point to vulnerable symbol (-1 if unreachable).
+    /// </summary>
+    [JsonPropertyName("pathLength")]
+    public int? PathLength { get; init; }
+}
+
+/// <summary>
+/// Result of a single gate evaluation.
+/// </summary>
+public sealed record PolicyGateResult
+{
+    /// <summary>
+    /// Name of the gate.
+    /// </summary>
+    [JsonPropertyName("name")]
+    public required string Name { get; init; }
+
+    /// <summary>
+    /// Result of the gate evaluation.
+    /// </summary>
+    [JsonPropertyName("result")]
+    public required PolicyGateResultType Result { get; init; }
+
+    /// <summary>
+    /// Reason for the result.
+    /// </summary>
+    [JsonPropertyName("reason")]
+    public required string Reason { get; init; }
+
+    /// <summary>
+    /// Additional note if result is pass_with_note.
+    /// </summary>
+    [JsonPropertyName("note")]
+    public string? Note { get; init; }
+}
+
+/// <summary>
+/// Overall gate decision type.
+/// </summary>
+[JsonConverter(typeof(JsonStringEnumConverter<PolicyGateDecisionType>))]
+public enum PolicyGateDecisionType
+{
+    /// <summary>
+    /// Status change is allowed.
+    /// </summary>
+    [JsonPropertyName("allow")]
+    Allow,
+
+    /// <summary>
+    /// Status change is blocked.
+    /// </summary>
+    [JsonPropertyName("block")]
+    Block,
+
+    /// <summary>
+    /// Status change is allowed with warning.
+    /// </summary>
+    [JsonPropertyName("warn")]
+    Warn
+}
+
+/// <summary>
+/// Individual gate result type.
+/// </summary>
+[JsonConverter(typeof(JsonStringEnumConverter<PolicyGateResultType>))]
+public enum PolicyGateResultType
+{
+    /// <summary>
+    /// Gate passed.
+    /// </summary>
+    [JsonPropertyName("pass")]
+    Pass,
+
+    /// <summary>
+    /// Gate passed with advisory note.
+    /// </summary>
+    [JsonPropertyName("pass_with_note")]
+    PassWithNote,
+
+    /// <summary>
+    /// Gate emitted a warning.
+    /// </summary>
+    [JsonPropertyName("warn")]
+    Warn,
+
+    /// <summary>
+    /// Gate blocked the request.
+    /// </summary>
+    [JsonPropertyName("block")]
+    Block,
+
+    /// <summary>
+    /// Gate was skipped (not applicable).
+    /// </summary>
+    [JsonPropertyName("skip")]
+    Skip
+}
+
+/// <summary>
+/// Request to evaluate policy gates for a VEX status change.
+/// </summary>
+public sealed record PolicyGateRequest
+{
+    /// <summary>
+    /// Tenant identifier.
+    /// </summary>
+    public required string TenantId { get; init; }
+
+    /// <summary>
+    /// Vulnerability identifier.
+    /// </summary>
+    public string? VulnId { get; init; }
+
+    /// <summary>
+    /// Package URL.
+    /// </summary>
+    public string? Purl { get; init; }
+
+    /// <summary>
+    /// Symbol identifier.
+    /// </summary>
+    public string? SymbolId { get; init; }
+
+    /// <summary>
+    /// Scan identifier.
+    /// </summary>
+    public string? ScanId { get; init; }
+
+    /// <summary>
+    /// Requested VEX status (not_affected, affected, under_investigation, fixed).
+    /// </summary>
+    public required string RequestedStatus { get; init; }
+
+    /// <summary>
+    /// Justification for the status (required for some statuses).
+    /// </summary>
+    public string? Justification { get; init; }
+
+    /// <summary>
+    /// v1 lattice state code.
+    /// </summary>
+    public string? LatticeState { get; init; }
+
+    /// <summary>
+    /// Uncertainty tier.
+    /// </summary>
+    public string? UncertaintyTier { get; init; }
+
+    /// <summary>
+    /// BLAKE3 graph hash.
+    /// </summary>
+    public string? GraphHash { get; init; }
+
+    /// <summary>
+    /// Risk score.
+    /// </summary>
+    public double? RiskScore { get; init; }
+
+    /// <summary>
+    /// Confidence score.
+    /// </summary>
+    public double? Confidence { get; init; }
+
+    /// <summary>
+    /// Whether runtime evidence exists.
+    /// </summary>
+    public bool HasRuntimeEvidence { get; init; }
+
+    /// <summary>
+    /// Path length from entry point.
+    /// </summary>
+    public int? PathLength { get; init; }
+
+    /// <summary>
+    /// Whether to allow override (requires permission).
+    /// </summary>
+    public bool AllowOverride { get; init; }
+
+    /// <summary>
+    /// Override justification if AllowOverride is true.
+    /// </summary>
+    public string? OverrideJustification { get; init; }
+}

src/Policy/StellaOps.Policy.Engine/Gates/PolicyGateEvaluator.cs

@@ -0,0 +1,746 @@
+using System.Collections.Immutable;
+using System.Globalization;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Options;
+
+namespace StellaOps.Policy.Engine.Gates;
+
+/// <summary>
+/// Evaluates policy gates for VEX status transitions.
+/// Gates ensure that status changes are backed by sufficient evidence.
+/// </summary>
+public interface IPolicyGateEvaluator
+{
+    /// <summary>
+    /// Evaluates all policy gates for a VEX status change request.
+    /// </summary>
+    /// <param name="request">The gate evaluation request.</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>The gate decision.</returns>
+    Task<PolicyGateDecision> EvaluateAsync(PolicyGateRequest request, CancellationToken cancellationToken = default);
+}
+
+/// <summary>
+/// Default implementation of <see cref="IPolicyGateEvaluator"/>.
+/// </summary>
+public sealed class PolicyGateEvaluator : IPolicyGateEvaluator
+{
+    private readonly IOptionsMonitor<PolicyGateOptions> _options;
+    private readonly TimeProvider _timeProvider;
+    private readonly ILogger<PolicyGateEvaluator> _logger;
+
+    // VEX statuses
+    private const string StatusNotAffected = "not_affected";
+    private const string StatusAffected = "affected";
+    private const string StatusUnderInvestigation = "under_investigation";
+    private const string StatusFixed = "fixed";
+
+    // Lattice states (v1)
+    private const string LatticeUnknown = "U";
+    private const string LatticeStaticallyReachable = "SR";
+    private const string LatticeStaticallyUnreachable = "SU";
+    private const string LatticeRuntimeObserved = "RO";
+    private const string LatticeRuntimeUnobserved = "RU";
+    private const string LatticeConfirmedReachable = "CR";
+    private const string LatticeConfirmedUnreachable = "CU";
+    private const string LatticeContested = "X";
+
+    // Uncertainty tiers
+    private const string TierT1 = "T1";
+    private const string TierT2 = "T2";
+    private const string TierT3 = "T3";
+    private const string TierT4 = "T4";
+
+    public PolicyGateEvaluator(
+        IOptionsMonitor<PolicyGateOptions> options,
+        TimeProvider timeProvider,
+        ILogger<PolicyGateEvaluator> logger)
+    {
+        _options = options ?? throw new ArgumentNullException(nameof(options));
+        _timeProvider = timeProvider ?? throw new ArgumentNullException(nameof(timeProvider));
+        _logger = logger ?? throw new ArgumentNullException(nameof(logger));
+    }
+
+    /// <inheritdoc/>
+    public Task<PolicyGateDecision> EvaluateAsync(PolicyGateRequest request, CancellationToken cancellationToken = default)
+    {
+        ArgumentNullException.ThrowIfNull(request);
+
+        var options = _options.CurrentValue;
+        var now = _timeProvider.GetUtcNow();
+
+        // Build gate ID
+        var gateId = $"gate:vex:{request.RequestedStatus}:{now:O}";
+
+        // Build subject
+        var subject = new PolicyGateSubject
+        {
+            VulnId = request.VulnId,
+            Purl = request.Purl,
+            SymbolId = request.SymbolId,
+            ScanId = request.ScanId
+        };
+
+        // Build evidence
+        var evidence = new PolicyGateEvidence
+        {
+            LatticeState = request.LatticeState,
+            UncertaintyTier = request.UncertaintyTier,
+            GraphHash = request.GraphHash,
+            RiskScore = request.RiskScore,
+            Confidence = request.Confidence,
+            HasRuntimeEvidence = request.HasRuntimeEvidence,
+            PathLength = request.PathLength
+        };
+
+        // If gates are disabled, allow everything
+        if (!options.Enabled)
+        {
+            return Task.FromResult(CreateAllowDecision(gateId, request.RequestedStatus, subject, evidence, now, "Gates disabled"));
+        }
+
+        // Evaluate gates in order: Evidence -> Lattice -> Uncertainty -> Confidence
+        var gateResults = new List<PolicyGateResult>(4);
+        string? blockedBy = null;
+        string? blockReason = null;
+        string? suggestion = null;
+        var warnings = new List<string>();
+
+        // 1. Evidence Completeness Gate
+        var evidenceResult = EvaluateEvidenceCompletenessGate(request, options.EvidenceCompleteness);
+        gateResults.Add(evidenceResult);
+        if (evidenceResult.Result == PolicyGateResultType.Block)
+        {
+            blockedBy = evidenceResult.Name;
+            blockReason = evidenceResult.Reason;
+            suggestion = GetEvidenceSuggestion(request.RequestedStatus);
+        }
+        else if (evidenceResult.Result == PolicyGateResultType.Warn || evidenceResult.Result == PolicyGateResultType.PassWithNote)
+        {
+            warnings.Add(evidenceResult.Reason);
+        }
+
+        // 2. Lattice State Gate (only if not already blocked)
+        if (blockedBy is null)
+        {
+            var latticeResult = EvaluateLatticeStateGate(request, options.LatticeState);
+            gateResults.Add(latticeResult);
+            if (latticeResult.Result == PolicyGateResultType.Block)
+            {
+                blockedBy = latticeResult.Name;
+                blockReason = latticeResult.Reason;
+                suggestion = GetLatticeSuggestion(request.LatticeState, request.RequestedStatus);
+            }
+            else if (latticeResult.Result == PolicyGateResultType.Warn || latticeResult.Result == PolicyGateResultType.PassWithNote)
+            {
+                warnings.Add(latticeResult.Note ?? latticeResult.Reason);
+            }
+        }
+
+        // 3. Uncertainty Tier Gate (only if not already blocked)
+        if (blockedBy is null)
+        {
+            var uncertaintyResult = EvaluateUncertaintyTierGate(request, options.UncertaintyTier);
+            gateResults.Add(uncertaintyResult);
+            if (uncertaintyResult.Result == PolicyGateResultType.Block)
+            {
+                blockedBy = uncertaintyResult.Name;
+                blockReason = uncertaintyResult.Reason;
+                suggestion = GetUncertaintySuggestion(request.UncertaintyTier);
+            }
+            else if (uncertaintyResult.Result == PolicyGateResultType.Warn || uncertaintyResult.Result == PolicyGateResultType.PassWithNote)
+            {
+                warnings.Add(uncertaintyResult.Note ?? uncertaintyResult.Reason);
+            }
+        }
+
+        // 4. Confidence Threshold Gate (only if not already blocked)
+        if (blockedBy is null && request.Confidence.HasValue)
+        {
+            var confidenceResult = EvaluateConfidenceGate(request, options.EvidenceCompleteness);
+            gateResults.Add(confidenceResult);
+            if (confidenceResult.Result == PolicyGateResultType.Warn || confidenceResult.Result == PolicyGateResultType.PassWithNote)
+            {
+                warnings.Add(confidenceResult.Note ?? confidenceResult.Reason);
+            }
+        }
+
+        // Build final decision
+        PolicyGateDecisionType decision;
+        string? advisory = null;
+
+        if (blockedBy is not null)
+        {
+            // Check for override
+            if (request.AllowOverride && CanOverride(request, options.Override))
+            {
+                decision = PolicyGateDecisionType.Warn;
+                advisory = $"Override accepted: {request.OverrideJustification}";
+                _logger.LogInformation(
+                    "Gate {Gate} overridden for {Status} on {Vuln}/{Purl}: {Justification}",
+                    blockedBy, request.RequestedStatus, request.VulnId, request.Purl, request.OverrideJustification);
+            }
+            else
+            {
+                decision = PolicyGateDecisionType.Block;
+                _logger.LogInformation(
+                    "Gate {Gate} blocked {Status} on {Vuln}/{Purl}: {Reason}",
+                    blockedBy, request.RequestedStatus, request.VulnId, request.Purl, blockReason);
+            }
+        }
+        else if (warnings.Count > 0)
+        {
+            decision = PolicyGateDecisionType.Warn;
+            advisory = string.Join("; ", warnings);
+        }
+        else
+        {
+            decision = PolicyGateDecisionType.Allow;
+        }
+
+        var result = new PolicyGateDecision
+        {
+            GateId = gateId,
+            RequestedStatus = request.RequestedStatus,
+            Subject = subject,
+            Evidence = evidence,
+            Gates = gateResults.ToImmutableArray(),
+            Decision = decision,
+            Advisory = advisory,
+            BlockedBy = blockedBy,
+            BlockReason = blockReason,
+            Suggestion = suggestion,
+            DecidedAt = now
+        };
+
+        return Task.FromResult(result);
+    }
+
+    private PolicyGateResult EvaluateEvidenceCompletenessGate(PolicyGateRequest request, EvidenceCompletenessGateOptions options)
+    {
+        var status = request.RequestedStatus?.ToLowerInvariant() ?? string.Empty;
+
+        switch (status)
+        {
+            case StatusNotAffected:
+                // Require graph hash
+                if (options.RequireGraphHashForNotAffected && string.IsNullOrWhiteSpace(request.GraphHash))
+                {
+                    return new PolicyGateResult
+                    {
+                        Name = "EvidenceCompleteness",
+                        Result = PolicyGateResultType.Block,
+                        Reason = "graphHash (DSSE-attested) is required for not_affected"
+                    };
+                }
+
+                // Require path analysis
+                if (options.RequirePathAnalysisForNotAffected && request.PathLength is null)
+                {
+                    return new PolicyGateResult
+                    {
+                        Name = "EvidenceCompleteness",
+                        Result = PolicyGateResultType.Block,
+                        Reason = "pathAnalysis.pathLength is required for not_affected"
+                    };
+                }
+
+                return new PolicyGateResult
+                {
+                    Name = "EvidenceCompleteness",
+                    Result = PolicyGateResultType.Pass,
+                    Reason = "Required evidence present for not_affected"
+                };
+
+            case StatusAffected:
+                if (options.WarnNoEvidenceForAffected &&
+                    string.IsNullOrWhiteSpace(request.GraphHash) &&
+                    !request.HasRuntimeEvidence)
+                {
+                    return new PolicyGateResult
+                    {
+                        Name = "EvidenceCompleteness",
+                        Result = PolicyGateResultType.Warn,
+                        Reason = "No graphHash or runtimeProbe evidence for affected status"
+                    };
+                }
+
+                return new PolicyGateResult
+                {
+                    Name = "EvidenceCompleteness",
+                    Result = PolicyGateResultType.Pass,
+                    Reason = "Evidence present for affected"
+                };
+
+            case StatusUnderInvestigation:
+            case StatusFixed:
+                return new PolicyGateResult
+                {
+                    Name = "EvidenceCompleteness",
+                    Result = PolicyGateResultType.Pass,
+                    Reason = $"No evidence requirements for {status}"
+                };
+
+            default:
+                return new PolicyGateResult
+                {
+                    Name = "EvidenceCompleteness",
+                    Result = PolicyGateResultType.Skip,
+                    Reason = $"Unknown status: {status}"
+                };
+        }
+    }
+
+    private PolicyGateResult EvaluateLatticeStateGate(PolicyGateRequest request, LatticeStateGateOptions options)
+    {
+        var status = request.RequestedStatus?.ToLowerInvariant() ?? string.Empty;
+        var latticeState = request.LatticeState?.ToUpperInvariant() ?? LatticeUnknown;
+
+        switch (status)
+        {
+            case StatusNotAffected:
+                return EvaluateLatticeForNotAffected(latticeState, request.Justification, options);
+
+            case StatusAffected:
+                return EvaluateLatticeForAffected(latticeState);
+
+            case StatusUnderInvestigation:
+                return new PolicyGateResult
+                {
+                    Name = "LatticeState",
+                    Result = PolicyGateResultType.Pass,
+                    Reason = "Any lattice state allows under_investigation (safe default)"
+                };
+
+            case StatusFixed:
+                return new PolicyGateResult
+                {
+                    Name = "LatticeState",
+                    Result = PolicyGateResultType.Pass,
+                    Reason = "Any lattice state allows fixed (remediation action)"
+                };
+
+            default:
+                return new PolicyGateResult
+                {
+                    Name = "LatticeState",
+                    Result = PolicyGateResultType.Skip,
+                    Reason = $"Unknown status: {status}"
+                };
+        }
+    }
+
+    private PolicyGateResult EvaluateLatticeForNotAffected(string latticeState, string? justification, LatticeStateGateOptions options)
+    {
+        switch (latticeState)
+        {
+            case LatticeConfirmedUnreachable:
+                return new PolicyGateResult
+                {
+                    Name = "LatticeState",
+                    Result = PolicyGateResultType.Pass,
+                    Reason = "CU (ConfirmedUnreachable) allows not_affected"
+                };
+
+            case LatticeStaticallyUnreachable:
+                if (!options.AllowSUForNotAffected)
+                {
+                    return new PolicyGateResult
+                    {
+                        Name = "LatticeState",
+                        Result = PolicyGateResultType.Block,
+                        Reason = "SU (StaticallyUnreachable) not allowed for not_affected (configuration)"
+                    };
+                }
+
+                if (options.RequireJustificationForWeakStates && string.IsNullOrWhiteSpace(justification))
+                {
+                    return new PolicyGateResult
+                    {
+                        Name = "LatticeState",
+                        Result = PolicyGateResultType.Block,
+                        Reason = "SU requires justification for not_affected"
+                    };
+                }
+
+                return new PolicyGateResult
+                {
+                    Name = "LatticeState",
+                    Result = PolicyGateResultType.PassWithNote,
+                    Reason = "SU allows not_affected with warning",
+                    Note = "Static analysis only; no runtime confirmation"
+                };
+
+            case LatticeRuntimeUnobserved:
+                if (!options.AllowRUForNotAffected)
+                {
+                    return new PolicyGateResult
+                    {
+                        Name = "LatticeState",
+                        Result = PolicyGateResultType.Block,
+                        Reason = "RU (RuntimeUnobserved) not allowed for not_affected (configuration)"
+                    };
+                }
+
+                if (options.RequireJustificationForWeakStates && string.IsNullOrWhiteSpace(justification))
+                {
+                    return new PolicyGateResult
+                    {
+                        Name = "LatticeState",
+                        Result = PolicyGateResultType.Block,
+                        Reason = "RU requires justification for not_affected"
+                    };
+                }
+
+                return new PolicyGateResult
+                {
+                    Name = "LatticeState",
+                    Result = PolicyGateResultType.PassWithNote,
+                    Reason = "RU allows not_affected with warning",
+                    Note = "Runtime unobserved; may be reachable but untested code path"
+                };
+
+            case LatticeContested:
+                if (options.BlockContestedForDefinitiveStatuses)
+                {
+                    return new PolicyGateResult
+                    {
+                        Name = "LatticeState",
+                        Result = PolicyGateResultType.Block,
+                        Reason = "X (Contested) incompatible with not_affected; conflicting static/runtime evidence"
+                    };
+                }
+
+                return new PolicyGateResult
+                {
+                    Name = "LatticeState",
+                    Result = PolicyGateResultType.Warn,
+                    Reason = "X (Contested) requires triage before not_affected"
+                };
+
+            case LatticeUnknown:
+            case LatticeStaticallyReachable:
+            case LatticeRuntimeObserved:
+            case LatticeConfirmedReachable:
+                return new PolicyGateResult
+                {
+                    Name = "LatticeState",
+                    Result = PolicyGateResultType.Block,
+                    Reason = $"{latticeState} incompatible with not_affected"
+                };
+
+            default:
+                return new PolicyGateResult
+                {
+                    Name = "LatticeState",
+                    Result = PolicyGateResultType.Block,
+                    Reason = $"Unknown lattice state {latticeState} cannot justify not_affected"
+                };
+        }
+    }
+
+    private PolicyGateResult EvaluateLatticeForAffected(string latticeState)
+    {
+        switch (latticeState)
+        {
+            case LatticeConfirmedReachable:
+                return new PolicyGateResult
+                {
+                    Name = "LatticeState",
+                    Result = PolicyGateResultType.Pass,
+                    Reason = "CR (ConfirmedReachable) confirms affected"
+                };
+
+            case LatticeStaticallyReachable:
+            case LatticeRuntimeObserved:
+                return new PolicyGateResult
+                {
+                    Name = "LatticeState",
+                    Result = PolicyGateResultType.Pass,
+                    Reason = $"{latticeState} supports affected"
+                };
+
+            case LatticeUnknown:
+            case LatticeStaticallyUnreachable:
+            case LatticeRuntimeUnobserved:
+            case LatticeConfirmedUnreachable:
+            case LatticeContested:
+                return new PolicyGateResult
+                {
+                    Name = "LatticeState",
+                    Result = PolicyGateResultType.Warn,
+                    Reason = $"{latticeState} may indicate false positive for affected",
+                    Note = "Consider review: evidence suggests code may not be reachable"
+                };
+
+            default:
+                return new PolicyGateResult
+                {
+                    Name = "LatticeState",
+                    Result = PolicyGateResultType.Pass,
+                    Reason = "Unknown lattice state; allowing affected as safe default"
+                };
+        }
+    }
+
+    private PolicyGateResult EvaluateUncertaintyTierGate(PolicyGateRequest request, UncertaintyTierGateOptions options)
+    {
+        var status = request.RequestedStatus?.ToLowerInvariant() ?? string.Empty;
+        var tier = request.UncertaintyTier?.ToUpperInvariant() ?? TierT4;
+
+        switch (status)
+        {
+            case StatusNotAffected:
+                return EvaluateUncertaintyForNotAffected(tier, options);
+
+            case StatusAffected:
+                return EvaluateUncertaintyForAffected(tier, options);
+
+            case StatusUnderInvestigation:
+            case StatusFixed:
+                return new PolicyGateResult
+                {
+                    Name = "UncertaintyTier",
+                    Result = PolicyGateResultType.Pass,
+                    Reason = $"No uncertainty requirements for {status}"
+                };
+
+            default:
+                return new PolicyGateResult
+                {
+                    Name = "UncertaintyTier",
+                    Result = PolicyGateResultType.Skip,
+                    Reason = $"Unknown status: {status}"
+                };
+        }
+    }
+
+    private PolicyGateResult EvaluateUncertaintyForNotAffected(string tier, UncertaintyTierGateOptions options)
+    {
+        switch (tier)
+        {
+            case TierT1:
+                if (options.BlockT1ForNotAffected)
+                {
+                    return new PolicyGateResult
+                    {
+                        Name = "UncertaintyTier",
+                        Result = PolicyGateResultType.Block,
+                        Reason = "T1 (High) uncertainty blocks not_affected; require human review"
+                    };
+                }
+
+                return new PolicyGateResult
+                {
+                    Name = "UncertaintyTier",
+                    Result = PolicyGateResultType.Warn,
+                    Reason = "T1 (High) uncertainty; not_affected may be premature"
+                };
+
+            case TierT2:
+                if (options.WarnT2ForNotAffected)
+                {
+                    return new PolicyGateResult
+                    {
+                        Name = "UncertaintyTier",
+                        Result = PolicyGateResultType.Warn,
+                        Reason = "T2 (Medium) uncertainty; explicit override recommended",
+                        Note = "Flag for review; decisions may need re-evaluation"
+                    };
+                }
+
+                return new PolicyGateResult
+                {
+                    Name = "UncertaintyTier",
+                    Result = PolicyGateResultType.Pass,
+                    Reason = "T2 (Medium) uncertainty allowed for not_affected"
+                };
+
+            case TierT3:
+                return new PolicyGateResult
+                {
+                    Name = "UncertaintyTier",
+                    Result = PolicyGateResultType.PassWithNote,
+                    Reason = "T3 (Low) uncertainty allows not_affected",
+                    Note = "Advisory: Low uncertainty present"
+                };
+
+            case TierT4:
+                return new PolicyGateResult
+                {
+                    Name = "UncertaintyTier",
+                    Result = PolicyGateResultType.Pass,
+                    Reason = "T4 (Negligible) uncertainty; not_affected allowed"
+                };
+
+            default:
+                return new PolicyGateResult
+                {
+                    Name = "UncertaintyTier",
+                    Result = PolicyGateResultType.Warn,
+                    Reason = $"Unknown uncertainty tier {tier}"
+                };
+        }
+    }
+
+    private PolicyGateResult EvaluateUncertaintyForAffected(string tier, UncertaintyTierGateOptions options)
+    {
+        switch (tier)
+        {
+            case TierT1:
+                if (options.ReviewT1ForAffected)
+                {
+                    return new PolicyGateResult
+                    {
+                        Name = "UncertaintyTier",
+                        Result = PolicyGateResultType.Warn,
+                        Reason = "T1 (High) uncertainty for affected; may be false positive",
+                        Note = "Review required: high uncertainty suggests reachability analysis incomplete"
+                    };
+                }
+
+                return new PolicyGateResult
+                {
+                    Name = "UncertaintyTier",
+                    Result = PolicyGateResultType.Pass,
+                    Reason = "T1 (High) uncertainty; affected allowed as safe default"
+                };
+
+            case TierT2:
+            case TierT3:
+            case TierT4:
+                return new PolicyGateResult
+                {
+                    Name = "UncertaintyTier",
+                    Result = PolicyGateResultType.Pass,
+                    Reason = $"{tier} uncertainty allows affected"
+                };
+
+            default:
+                return new PolicyGateResult
+                {
+                    Name = "UncertaintyTier",
+                    Result = PolicyGateResultType.Pass,
+                    Reason = "Unknown uncertainty tier; allowing affected as safe default"
+                };
+        }
+    }
+
+    private PolicyGateResult EvaluateConfidenceGate(PolicyGateRequest request, EvidenceCompletenessGateOptions options)
+    {
+        var status = request.RequestedStatus?.ToLowerInvariant() ?? string.Empty;
+        var confidence = request.Confidence ?? 1.0;
+
+        if (status == StatusNotAffected)
+        {
+            if (confidence < options.MinConfidenceWarning)
+            {
+                return new PolicyGateResult
+                {
+                    Name = "ConfidenceThreshold",
+                    Result = PolicyGateResultType.Warn,
+                    Reason = string.Create(CultureInfo.InvariantCulture, $"Confidence {confidence:P0} below warning threshold {options.MinConfidenceWarning:P0}"),
+                    Note = "Low confidence in reachability analysis"
+                };
+            }
+
+            if (confidence < options.MinConfidenceForNotAffected)
+            {
+                return new PolicyGateResult
+                {
+                    Name = "ConfidenceThreshold",
+                    Result = PolicyGateResultType.Warn,
+                    Reason = string.Create(CultureInfo.InvariantCulture, $"Confidence {confidence:P0} below recommended {options.MinConfidenceForNotAffected:P0}"),
+                    Note = "Consider gathering additional evidence"
+                };
+            }
+        }
+
+        return new PolicyGateResult
+        {
+            Name = "ConfidenceThreshold",
+            Result = PolicyGateResultType.Pass,
+            Reason = string.Create(CultureInfo.InvariantCulture, $"Confidence {confidence:P0} meets requirements")
+        };
+    }
+
+    private static bool CanOverride(PolicyGateRequest request, OverrideOptions options)
+    {
+        if (!request.AllowOverride)
+        {
+            return false;
+        }
+
+        if (options.RequireJustification)
+        {
+            if (string.IsNullOrWhiteSpace(request.OverrideJustification))
+            {
+                return false;
+            }
+
+            if (request.OverrideJustification.Length < options.MinJustificationLength)
+            {
+                return false;
+            }
+        }
+
+        return true;
+    }
+
+    private static PolicyGateDecision CreateAllowDecision(
+        string gateId,
+        string requestedStatus,
+        PolicyGateSubject subject,
+        PolicyGateEvidence evidence,
+        DateTimeOffset decidedAt,
+        string reason)
+    {
+        return new PolicyGateDecision
+        {
+            GateId = gateId,
+            RequestedStatus = requestedStatus,
+            Subject = subject,
+            Evidence = evidence,
+            Gates = ImmutableArray.Create(new PolicyGateResult
+            {
+                Name = "Bypass",
+                Result = PolicyGateResultType.Pass,
+                Reason = reason
+            }),
+            Decision = PolicyGateDecisionType.Allow,
+            Advisory = reason,
+            DecidedAt = decidedAt
+        };
+    }
+
+    private static string GetEvidenceSuggestion(string status) => status switch
+    {
+        StatusNotAffected => "Submit DSSE-attested call graph with path analysis",
+        StatusAffected => "Consider providing graph hash or runtime probe evidence",
+        _ => "Provide additional evidence"
+    };
+
+    private static string GetLatticeSuggestion(string? latticeState, string status)
+    {
+        if (status == StatusNotAffected)
+        {
+            return latticeState switch
+            {
+                LatticeContested => "Resolve contested state through triage before claiming not_affected",
+                LatticeStaticallyReachable or LatticeRuntimeObserved or LatticeConfirmedReachable =>
+                    "Submit runtime probe evidence showing unreachability or change to under_investigation",
+                LatticeUnknown => "Run reachability analysis to determine lattice state",
+                _ => "Provide evidence to support not_affected claim"
+            };
+        }
+
+        return "Review evidence and adjust status accordingly";
+    }
+
+    private static string GetUncertaintySuggestion(string? tier) => tier switch
+    {
+        TierT1 => "Reduce uncertainty: resolve missing symbol resolution, verify PURL mappings, or provide trusted advisory sources",
+        TierT2 => "Consider providing override with justification or reducing uncertainty through additional analysis",
+        _ => "Review uncertainty sources and address where possible"
+    };
+}

src/Policy/StellaOps.Policy.Engine/Gates/PolicyGateOptions.cs

@@ -0,0 +1,136 @@
+namespace StellaOps.Policy.Engine.Gates;
+
+/// <summary>
+/// Configuration options for policy gates.
+/// </summary>
+public sealed class PolicyGateOptions
+{
+    /// <summary>
+    /// Configuration section name.
+    /// </summary>
+    public const string SectionName = "PolicyGates";
+
+    /// <summary>
+    /// Lattice state gate options.
+    /// </summary>
+    public LatticeStateGateOptions LatticeState { get; set; } = new();
+
+    /// <summary>
+    /// Uncertainty tier gate options.
+    /// </summary>
+    public UncertaintyTierGateOptions UncertaintyTier { get; set; } = new();
+
+    /// <summary>
+    /// Evidence completeness gate options.
+    /// </summary>
+    public EvidenceCompletenessGateOptions EvidenceCompleteness { get; set; } = new();
+
+    /// <summary>
+    /// Override mechanism options.
+    /// </summary>
+    public OverrideOptions Override { get; set; } = new();
+
+    /// <summary>
+    /// Whether gates are enabled.
+    /// </summary>
+    public bool Enabled { get; set; } = true;
+}
+
+/// <summary>
+/// Configuration options for the lattice state gate.
+/// </summary>
+public sealed class LatticeStateGateOptions
+{
+    /// <summary>
+    /// Allow StaticallyUnreachable (SU) state for not_affected with warning.
+    /// </summary>
+    public bool AllowSUForNotAffected { get; set; } = true;
+
+    /// <summary>
+    /// Allow RuntimeUnobserved (RU) state for not_affected with warning.
+    /// </summary>
+    public bool AllowRUForNotAffected { get; set; } = true;
+
+    /// <summary>
+    /// Require justification for weak states (SU, RU).
+    /// </summary>
+    public bool RequireJustificationForWeakStates { get; set; } = true;
+
+    /// <summary>
+    /// Block contested (X) state for definitive statuses.
+    /// </summary>
+    public bool BlockContestedForDefinitiveStatuses { get; set; } = true;
+}
+
+/// <summary>
+/// Configuration options for the uncertainty tier gate.
+/// </summary>
+public sealed class UncertaintyTierGateOptions
+{
+    /// <summary>
+    /// Block T1 (High) uncertainty for not_affected.
+    /// </summary>
+    public bool BlockT1ForNotAffected { get; set; } = true;
+
+    /// <summary>
+    /// Warn for T2 (Medium) uncertainty for not_affected.
+    /// </summary>
+    public bool WarnT2ForNotAffected { get; set; } = true;
+
+    /// <summary>
+    /// Require explicit override for T1 affected (possible false positive).
+    /// </summary>
+    public bool ReviewT1ForAffected { get; set; } = true;
+}
+
+/// <summary>
+/// Configuration options for the evidence completeness gate.
+/// </summary>
+public sealed class EvidenceCompletenessGateOptions
+{
+    /// <summary>
+    /// Require graph hash for not_affected.
+    /// </summary>
+    public bool RequireGraphHashForNotAffected { get; set; } = true;
+
+    /// <summary>
+    /// Minimum confidence threshold for not_affected.
+    /// </summary>
+    public double MinConfidenceForNotAffected { get; set; } = 0.8;
+
+    /// <summary>
+    /// Confidence threshold that triggers a warning.
+    /// </summary>
+    public double MinConfidenceWarning { get; set; } = 0.6;
+
+    /// <summary>
+    /// Require path analysis for not_affected.
+    /// </summary>
+    public bool RequirePathAnalysisForNotAffected { get; set; } = true;
+
+    /// <summary>
+    /// Warn if no graph hash or runtime probe for affected.
+    /// </summary>
+    public bool WarnNoEvidenceForAffected { get; set; } = true;
+}
+
+/// <summary>
+/// Configuration options for override mechanism.
+/// </summary>
+public sealed class OverrideOptions
+{
+    /// <summary>
+    /// Default expiration period for overrides in days.
+    /// </summary>
+    public int DefaultExpirationDays { get; set; } = 30;
+
+    /// <summary>
+    /// Require justification for all overrides.
+    /// </summary>
+    public bool RequireJustification { get; set; } = true;
+
+    /// <summary>
+    /// Minimum justification length.
+    /// </summary>
+    public int MinJustificationLength { get; set; } = 20;
+}

src/Policy/StellaOps.Policy.Engine/Services/PolicyRuntimeEvaluationService.cs

@@ -599,6 +599,8 @@ internal sealed class PolicyRuntimeEvaluationService
             Method: fact.Method.ToString().ToLowerInvariant(),
             EvidenceRef: fact.EvidenceRef ?? fact.EvidenceHash);
 
+        reachability = ApplyReachabilityEvidenceGate(reachability, fact.EvidenceRef);
+
         ReachabilityFacts.ReachabilityFactsTelemetry.RecordFactApplied(reachability.State);
         return request with { Reachability = reachability };
     }
@@ -652,6 +654,8 @@ internal sealed class PolicyRuntimeEvaluationService
                         Method: fact.Method.ToString().ToLowerInvariant(),
                         EvidenceRef: fact.EvidenceRef ?? fact.EvidenceHash);
 
+                    reachability = ApplyReachabilityEvidenceGate(reachability, fact.EvidenceRef);
+
                     ReachabilityFacts.ReachabilityFactsTelemetry.RecordFactApplied(reachability.State);
                     enriched.Add(request with { Reachability = reachability });
                 }
@@ -664,5 +668,21 @@ internal sealed class PolicyRuntimeEvaluationService
 
         return enriched;
     }
-}
 
+    private static PolicyEvaluationReachability ApplyReachabilityEvidenceGate(
+        PolicyEvaluationReachability reachability,
+        string? evidenceRef)
+    {
+        if (!reachability.IsUnreachable)
+        {
+            return reachability;
+        }
+
+        if (!reachability.IsHighConfidence || string.IsNullOrWhiteSpace(evidenceRef))
+        {
+            return reachability with { State = "under_investigation" };
+        }
+
+        return reachability;
+    }
+}

src/Policy/StellaOps.Policy.Engine/StellaOps.Policy.Engine.csproj

@@ -23,6 +23,7 @@
 
 
   <ItemGroup>
+    <ProjectReference Include="../../__Libraries/StellaOps.Messaging/StellaOps.Messaging.csproj" />
     <ProjectReference Include="../__Libraries/StellaOps.Policy/StellaOps.Policy.csproj" />
     <ProjectReference Include="../StellaOps.PolicyDsl/StellaOps.PolicyDsl.csproj" />
     <ProjectReference Include="../../__Libraries/StellaOps.Configuration/StellaOps.Configuration.csproj" />

src/Policy/StellaOps.Policy.Engine/TASKS.md

@@ -0,0 +1,7 @@
+# Policy Engine · Local Tasks
+
+This file mirrors sprint work for the Policy Engine module.
+
+| Task ID | Sprint | Status | Notes |
+| --- | --- | --- | --- |
+| `POLICY-GATE-401-033` | `docs/implplan/SPRINT_0401_0001_0001_reachability_evidence_chain.md` | DOING | Gate `unreachable` reachability facts: missing evidence ref or low confidence => `under_investigation`; add tests and docs. |