# Replayable Verdict Evaluation

## Module
Policy

## Status
IMPLEMENTED

## Description
Full replay engine that re-evaluates verdicts using stored snapshot inputs, producing match/mismatch reports with delta explanations when results differ. Exposed via API endpoints.

## Implementation Details
- **ReplayEngine**: `src/Policy/__Libraries/StellaOps.Policy/Replay/ReplayEngine.cs` (sealed class implements `IReplayEngine`)
  - `ReplayAsync(ReplayRequest)` -- full replay pipeline: load snapshot, resolve inputs, execute, compare, report
  - Uses frozen inputs from KnowledgeSnapshotManifest to ensure deterministic re-evaluation
  - Comparison with VerdictComparer produces ExactMatch, MatchWithinTolerance, or Mismatch
  - Delta report with FieldDeltas, FindingDeltas, and SuspectedCauses
- **ReplayRequest**: `src/Policy/__Libraries/StellaOps.Policy/Replay/ReplayRequest.cs`
  - ArtifactDigest, SnapshotId, OriginalVerdictId
  - ReplayOptions: CompareWithOriginal, AllowNetworkFetch=false, GenerateDetailedReport, ScoreTolerance=0.001
- **ReplayResult**: `src/Policy/__Libraries/StellaOps.Policy/Replay/ReplayResult.cs`
  - MatchStatus: ExactMatch, MatchWithinTolerance, Mismatch, NoComparison, ReplayFailed
  - ReplayedVerdict with Decision (Pass/Fail/PassWithExceptions/Indeterminate), Score, FindingIds
  - Duration tracking for performance monitoring
- **VerdictComparer**: `src/Policy/__Libraries/StellaOps.Policy/Replay/VerdictComparer.cs` -- deterministic comparison with configurable tolerance
- **KnowledgeSourceResolver**: `src/Policy/__Libraries/StellaOps.Policy/Replay/KnowledgeSourceResolver.cs` -- resolves snapshot source descriptors to data
- **SnapshotAwarePolicyEvaluator**: `src/Policy/__Libraries/StellaOps.Policy/Snapshots/SnapshotAwarePolicyEvaluator.cs` -- evaluation with pinned inputs
- **KnowledgeSnapshotManifest**: `src/Policy/__Libraries/StellaOps.Policy/Snapshots/KnowledgeSnapshotManifest.cs` -- content-addressed snapshot manifest

## E2E Test Plan
- [ ] Replay verdict with same snapshot and inputs; verify ExactMatch status
- [ ] Replay verdict after source data changed; verify Mismatch with SuspectedCauses listing changed source
- [ ] Replay with ScoreTolerance=0.01; introduce 0.005 score drift; verify MatchWithinTolerance
- [ ] Replay with ScoreTolerance=0.001; introduce 0.005 score drift; verify Mismatch with FieldDelta showing score difference
- [ ] Verify ReplayDeltaReport.FindingDeltas lists Added findings (present in replay, absent in original)
- [ ] Verify ReplayDeltaReport.FindingDeltas lists Removed findings (absent in replay, present in original)
- [ ] Replay with AllowNetworkFetch=false and missing bundled source; verify ReplayFailed
- [ ] Replay with CompareWithOriginal=false; verify NoComparison status, no DeltaReport
- [ ] Verify replay Duration is non-zero and reasonable
- [ ] POST replay endpoint; verify JSON response includes all ReplayResult fields