# Timeline Replay API

## Module
Timeline

## Status
IMPLEMENTED

## Description
REST API endpoints for querying and replaying HLC-ordered events: GET /timeline/{correlationId} with service/kind/HLC-range/pagination filters, critical path analysis endpoint, and integration with StellaOps.Replay.Core for deterministic replay at a specific HLC timestamp.

## Implementation Details
- **ReplayEndpoints**: `src/Timeline/StellaOps.Timeline.WebService/Endpoints/ReplayEndpoints.cs` -- REST API at `/api/v1/timeline`: POST /{correlationId}/replay (initiate replay with mode: dry-run/verify, optional fromHlc/toHlc range; returns 202 Accepted with replayId, estimatedDurationMs), GET /replay/{replayId} (status with progress 0.0-1.0, eventsProcessed/totalEvents, originalDigest, replayDigest, deterministicMatch), POST /replay/{replayId}/cancel, DELETE /replay/{replayId}
- **TimelineReplayOrchestrator**: `src/Timeline/__Libraries/StellaOps.Timeline.Core/Replay/TimelineReplayOrchestrator.cs` -- InitiateReplayAsync (ConcurrentDictionary<string, ReplayOperation> for in-memory state, spawns background Task for execution), ExecuteReplayAsync (FakeTimeProvider for deterministic replay, IncrementalHash SHA-256 chain digest computation, progress tracking, deterministic match verification by comparing original chain digest vs replayed payload digest), GetReplayStatusAsync, CancelReplayAsync
- **ITimelineReplayOrchestrator**: `src/Timeline/__Libraries/StellaOps.Timeline.Core/Replay/ITimelineReplayOrchestrator.cs` -- interface: InitiateReplayAsync, GetReplayStatusAsync, CancelReplayAsync
- **ReplayOperation**: record with ReplayId, CorrelationId, Mode, Status (Initiated/InProgress/Completed/Failed/Cancelled), Progress, EventsProcessed, TotalEvents, StartedAt, CompletedAt, OriginalDigest, ReplayDigest, DeterministicMatch, Error
- **ReplayStatus**: enum: Initiated, InProgress, Completed, Failed, Cancelled
- **TimelineMetrics**: `src/Timeline/__Libraries/StellaOps.Timeline.Core/Telemetry/TimelineMetrics.cs` -- RecordReplay(mode, outcome, eventCount, durationSeconds)
- **Tests**: `src/Timeline/__Tests/StellaOps.Timeline.WebService.Tests/ReplayOrchestratorIntegrationTests.cs`
- **Source**: SPRINT_20260107_003_002_BE_timeline_replay_api.md

## E2E Test Plan
- [ ] POST /api/v1/timeline/{correlationId}/replay returns 202 Accepted with replayId and estimatedDurationMs
- [ ] GET /replay/{replayId} returns progress from 0.0 to 1.0 with eventsProcessed and totalEvents
- [ ] Verify completed replay includes originalDigest and replayDigest (SHA-256 chain hashes)
- [ ] Verify deterministicMatch is true when replayed output matches original event chain
- [ ] Test dry-run mode processes all events without side effects
- [ ] POST /replay/{replayId}/cancel stops an in-progress replay
- [ ] Verify cancelled replay cannot be restarted
- [ ] Test replay with HLC range (fromHlc/toHlc) replays only events within the range
- [ ] Verify replay of non-existent correlationId returns appropriate error