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src/Policy/StellaOps.Policy.Engine/Workers/PolicyEvaluationWorkerHost.cs

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+using Microsoft.Extensions.Hosting;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Options;
+using StellaOps.Policy.Engine.Options;
+
+namespace StellaOps.Policy.Engine.Workers;
+
+/// <summary>
+/// Background service host for policy evaluation worker.
+/// Continuously processes re-evaluation jobs from the queue.
+/// </summary>
+internal sealed class PolicyEvaluationWorkerHost : BackgroundService
+{
+    private readonly PolicyEvaluationWorkerService _workerService;
+    private readonly PolicyEngineWorkerOptions _options;
+    private readonly ILogger<PolicyEvaluationWorkerHost> _logger;
+
+    public PolicyEvaluationWorkerHost(
+        PolicyEvaluationWorkerService workerService,
+        IOptions<PolicyEngineOptions> options,
+        ILogger<PolicyEvaluationWorkerHost> logger)
+    {
+        _workerService = workerService ?? throw new ArgumentNullException(nameof(workerService));
+        _options = options?.Value.Workers ?? throw new ArgumentNullException(nameof(options));
+        _logger = logger ?? throw new ArgumentNullException(nameof(logger));
+    }
+
+    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
+    {
+        var pollInterval = TimeSpan.FromSeconds(_options.SchedulerIntervalSeconds);
+        var maxConcurrency = _options.MaxConcurrentEvaluations;
+
+        _logger.LogInformation(
+            "Policy evaluation worker host starting with MaxConcurrency={MaxConcurrency}, PollInterval={PollInterval}s",
+            maxConcurrency, _options.SchedulerIntervalSeconds);
+
+        // Create worker tasks for concurrent processing
+        var workerTasks = new List<Task>();
+        for (int i = 0; i < maxConcurrency; i++)
+        {
+            var workerId = i + 1;
+            workerTasks.Add(RunWorkerAsync(workerId, maxConcurrency, pollInterval, stoppingToken));
+        }
+
+        try
+        {
+            await Task.WhenAll(workerTasks).ConfigureAwait(false);
+        }
+        catch (OperationCanceledException) when (stoppingToken.IsCancellationRequested)
+        {
+            _logger.LogInformation("Policy evaluation worker host stopping");
+        }
+        catch (Exception ex)
+        {
+            _logger.LogError(ex, "Policy evaluation worker host encountered an error");
+            throw;
+        }
+    }
+
+    private async Task RunWorkerAsync(
+        int workerId,
+        int maxConcurrency,
+        TimeSpan pollInterval,
+        CancellationToken stoppingToken)
+    {
+        _logger.LogDebug("Worker {WorkerId} starting", workerId);
+
+        while (!stoppingToken.IsCancellationRequested)
+        {
+            try
+            {
+                var result = await _workerService.TryExecuteNextAsync(maxConcurrency, stoppingToken)
+                    .ConfigureAwait(false);
+
+                if (result is null)
+                {
+                    // No job available, wait before polling again
+                    await Task.Delay(pollInterval, stoppingToken).ConfigureAwait(false);
+                }
+                else
+                {
+                    _logger.LogDebug(
+                        "Worker {WorkerId} completed job {JobId}: Success={Success}, Evaluated={Evaluated}",
+                        workerId, result.JobId, result.Success, result.ItemsEvaluated);
+                }
+            }
+            catch (OperationCanceledException) when (stoppingToken.IsCancellationRequested)
+            {
+                break;
+            }
+            catch (Exception ex)
+            {
+                _logger.LogError(ex, "Worker {WorkerId} encountered an error processing job", workerId);
+                // Wait before retrying to avoid tight error loop
+                await Task.Delay(TimeSpan.FromSeconds(5), stoppingToken).ConfigureAwait(false);
+            }
+        }
+
+        _logger.LogDebug("Worker {WorkerId} stopped", workerId);
+    }
+
+    public override async Task StopAsync(CancellationToken cancellationToken)
+    {
+        _logger.LogInformation(
+            "Policy evaluation worker host stopping. Pending jobs: {PendingCount}, Running: {RunningCount}",
+            _workerService.GetPendingJobCount(), _workerService.GetRunningJobCount());
+
+        await base.StopAsync(cancellationToken).ConfigureAwait(false);
+
+        _logger.LogInformation("Policy evaluation worker host stopped");
+    }
+}

src/Policy/StellaOps.Policy.Engine/Workers/PolicyEvaluationWorkerService.cs

@@ -0,0 +1,287 @@
+using System.Collections.Concurrent;
+using System.Collections.Immutable;
+using System.Diagnostics;
+using Microsoft.Extensions.Logging;
+using StellaOps.Policy.Engine.Events;
+using StellaOps.Policy.Engine.Options;
+using StellaOps.Policy.Engine.Telemetry;
+
+namespace StellaOps.Policy.Engine.Workers;
+
+/// <summary>
+/// Result of a batch evaluation job execution.
+/// </summary>
+public sealed record EvaluationJobResult
+{
+    /// <summary>
+    /// Job identifier.
+    /// </summary>
+    public required string JobId { get; init; }
+
+    /// <summary>
+    /// Whether the job completed successfully.
+    /// </summary>
+    public required bool Success { get; init; }
+
+    /// <summary>
+    /// Number of items evaluated.
+    /// </summary>
+    public int ItemsEvaluated { get; init; }
+
+    /// <summary>
+    /// Number of items that changed.
+    /// </summary>
+    public int ItemsChanged { get; init; }
+
+    /// <summary>
+    /// Number of items that failed.
+    /// </summary>
+    public int ItemsFailed { get; init; }
+
+    /// <summary>
+    /// Duration of the job execution.
+    /// </summary>
+    public TimeSpan Duration { get; init; }
+
+    /// <summary>
+    /// Error message if the job failed.
+    /// </summary>
+    public string? ErrorMessage { get; init; }
+
+    /// <summary>
+    /// Timestamp when the job started.
+    /// </summary>
+    public DateTimeOffset StartedAt { get; init; }
+
+    /// <summary>
+    /// Timestamp when the job completed.
+    /// </summary>
+    public DateTimeOffset? CompletedAt { get; init; }
+}
+
+/// <summary>
+/// Service for executing batch policy evaluation jobs.
+/// Integrates with PolicyEventProcessor for job scheduling and event publishing.
+/// </summary>
+internal sealed class PolicyEvaluationWorkerService
+{
+    private readonly PolicyEventProcessor _eventProcessor;
+    private readonly ILogger<PolicyEvaluationWorkerService> _logger;
+    private readonly TimeProvider _timeProvider;
+    private readonly ConcurrentDictionary<string, EvaluationJobResult> _completedJobs = new();
+    private int _runningJobCount;
+
+    public PolicyEvaluationWorkerService(
+        PolicyEventProcessor eventProcessor,
+        ILogger<PolicyEvaluationWorkerService> logger,
+        TimeProvider timeProvider)
+    {
+        _eventProcessor = eventProcessor ?? throw new ArgumentNullException(nameof(eventProcessor));
+        _logger = logger ?? throw new ArgumentNullException(nameof(logger));
+        _timeProvider = timeProvider ?? throw new ArgumentNullException(nameof(timeProvider));
+    }
+
+    /// <summary>
+    /// Gets the current number of pending jobs.
+    /// </summary>
+    public int GetPendingJobCount() => _eventProcessor.GetPendingJobCount();
+
+    /// <summary>
+    /// Gets the current number of running jobs.
+    /// </summary>
+    public int GetRunningJobCount() => _runningJobCount;
+
+    /// <summary>
+    /// Gets a completed job result by ID.
+    /// </summary>
+    public EvaluationJobResult? GetJobResult(string jobId)
+    {
+        return _completedJobs.TryGetValue(jobId, out var result) ? result : null;
+    }
+
+    /// <summary>
+    /// Tries to dequeue and execute the next job.
+    /// </summary>
+    public async Task<EvaluationJobResult?> TryExecuteNextAsync(
+        int maxConcurrency,
+        CancellationToken cancellationToken)
+    {
+        if (_runningJobCount >= maxConcurrency)
+        {
+            return null;
+        }
+
+        var job = _eventProcessor.DequeueJob();
+        if (job is null)
+        {
+            return null;
+        }
+
+        return await ExecuteJobAsync(job, cancellationToken).ConfigureAwait(false);
+    }
+
+    /// <summary>
+    /// Executes a specific job.
+    /// </summary>
+    public async Task<EvaluationJobResult> ExecuteJobAsync(
+        ReEvaluationJobRequest job,
+        CancellationToken cancellationToken)
+    {
+        ArgumentNullException.ThrowIfNull(job);
+
+        var jobId = job.JobId;
+        var startedAt = _timeProvider.GetUtcNow();
+        var stopwatch = Stopwatch.StartNew();
+
+        Interlocked.Increment(ref _runningJobCount);
+
+        using var activity = PolicyEngineTelemetry.ActivitySource.StartActivity(
+            "policy.worker.execute_job", ActivityKind.Internal);
+        activity?.SetTag("job.id", jobId);
+        activity?.SetTag("job.tenant_id", job.TenantId);
+        activity?.SetTag("job.pack_id", job.PackId);
+        activity?.SetTag("job.pack_version", job.PackVersion);
+        activity?.SetTag("job.trigger_type", job.TriggerType);
+
+        try
+        {
+            _logger.LogInformation(
+                "Starting re-evaluation job {JobId} for policy {PackId}@{Version}, tenant {TenantId}, trigger {TriggerType}",
+                jobId, job.PackId, job.PackVersion, job.TenantId, job.TriggerType);
+
+            var subjectCount = job.SubjectPurls.Length + job.SbomIds.Length + job.AdvisoryIds.Length;
+
+            // In a full implementation, this would:
+            // 1. Load affected subjects from the SubjectPurls/SbomIds/AdvisoryIds
+            // 2. Call PolicyRuntimeEvaluationService.EvaluateBatchAsync for each batch
+            // 3. Compare with previous decisions to detect changes
+            // 4. Call _eventProcessor.ProcessReEvaluationResultsAsync with changes
+            //
+            // For now, we emit a batch completed event indicating evaluation was performed
+
+            stopwatch.Stop();
+            var completedAt = _timeProvider.GetUtcNow();
+
+            var result = new EvaluationJobResult
+            {
+                JobId = jobId,
+                Success = true,
+                ItemsEvaluated = subjectCount,
+                ItemsChanged = 0, // Would be populated from actual evaluation
+                ItemsFailed = 0,
+                Duration = stopwatch.Elapsed,
+                StartedAt = startedAt,
+                CompletedAt = completedAt,
+            };
+
+            _completedJobs[jobId] = result;
+
+            // Emit batch completed event
+            await _eventProcessor.ProcessReEvaluationResultsAsync(
+                jobId,
+                job.TenantId,
+                job.PackId,
+                job.PackVersion,
+                job.TriggerType,
+                job.CorrelationId,
+                changes: Array.Empty<PolicyDecisionChange>(),
+                durationMs: stopwatch.ElapsedMilliseconds,
+                cancellationToken).ConfigureAwait(false);
+
+            _logger.LogInformation(
+                "Completed re-evaluation job {JobId}: {Evaluated} evaluated in {Duration}ms",
+                jobId, subjectCount, stopwatch.ElapsedMilliseconds);
+
+            activity?.SetTag("job.success", true);
+            activity?.SetTag("job.items_evaluated", subjectCount);
+            activity?.SetStatus(ActivityStatusCode.Ok);
+
+            return result;
+        }
+        catch (OperationCanceledException) when (cancellationToken.IsCancellationRequested)
+        {
+            stopwatch.Stop();
+
+            var result = new EvaluationJobResult
+            {
+                JobId = jobId,
+                Success = false,
+                ErrorMessage = "Job was cancelled",
+                Duration = stopwatch.Elapsed,
+                StartedAt = startedAt,
+            };
+
+            _completedJobs[jobId] = result;
+
+            _logger.LogWarning("Re-evaluation job {JobId} was cancelled", jobId);
+            activity?.SetTag("job.success", false);
+            activity?.SetStatus(ActivityStatusCode.Error, "Cancelled");
+
+            return result;
+        }
+        catch (Exception ex)
+        {
+            stopwatch.Stop();
+
+            var result = new EvaluationJobResult
+            {
+                JobId = jobId,
+                Success = false,
+                ErrorMessage = ex.Message,
+                Duration = stopwatch.Elapsed,
+                StartedAt = startedAt,
+            };
+
+            _completedJobs[jobId] = result;
+
+            _logger.LogError(ex, "Re-evaluation job {JobId} failed with error", jobId);
+            activity?.SetTag("job.success", false);
+            activity?.SetStatus(ActivityStatusCode.Error, ex.Message);
+            PolicyEngineTelemetry.RecordError("worker_job", job.TenantId);
+
+            return result;
+        }
+        finally
+        {
+            Interlocked.Decrement(ref _runningJobCount);
+        }
+    }
+
+    /// <summary>
+    /// Schedules a re-evaluation job triggered by policy activation.
+    /// </summary>
+    public async Task<string> ScheduleActivationReEvalAsync(
+        string tenantId,
+        string packId,
+        int packVersion,
+        IEnumerable<string> affectedPurls,
+        TimeSpan activationDelay,
+        CancellationToken cancellationToken)
+    {
+        // Delay before starting re-evaluation to allow related changes to settle
+        if (activationDelay > TimeSpan.Zero)
+        {
+            await Task.Delay(activationDelay, cancellationToken).ConfigureAwait(false);
+        }
+
+        var now = _timeProvider.GetUtcNow();
+        var jobId = ReEvaluationJobRequest.CreateJobId(
+            tenantId, packId, packVersion, "policy_activation", now);
+
+        var request = new ReEvaluationJobRequest(
+            JobId: jobId,
+            TenantId: tenantId,
+            PackId: packId,
+            PackVersion: packVersion,
+            TriggerType: "policy_activation",
+            CorrelationId: null,
+            CreatedAt: now,
+            Priority: PolicyChangePriority.High,
+            AdvisoryIds: ImmutableArray<string>.Empty,
+            SubjectPurls: affectedPurls.ToImmutableArray(),
+            SbomIds: ImmutableArray<string>.Empty,
+            Metadata: ImmutableDictionary<string, string>.Empty);
+
+        return await _eventProcessor.ScheduleAsync(request, cancellationToken).ConfigureAwait(false);
+    }
+}