Replay

Reconstruct current aggregate state by applying all events from sequence 0 (or from a snapshot).

How It Works

┌─────────────┐
│  Snapshot   │  (optional optimization)
│  seq: 100   │
└──────┬──────┘
       │
       ▼
┌─────────────┐     ┌─────────────┐     ┌─────────────┐
│  Event 101  │ ──► │  Event 102  │ ──► │  Event 103  │
└─────────────┘     └─────────────┘     └─────────────┘
       │                                       │
       └───────────────────────────────────────┘
                         │
                         ▼
                  ┌─────────────┐
                  │Current State│
                  │  seq: 103   │
                  └─────────────┘

When Replay Happens

1. Aggregate load: Before processing a command
2. Projector startup: Catching up on missed events
3. Debugging: Understanding how state evolved
4. Recovery: Rebuilding state after data loss

Replay vs Temporal Query

Aspect	Replay	Temporal Query
Target	Current state	Historical state
Events used	All (or from snapshot)	Up to timestamp/sequence
Use case	Normal operation	Audit, debugging

Optimization

Snapshots avoid replaying all events by caching state at checkpoints.