wifi-densepose/docs/adr/coherence-engine/ADR-CE-004-signed-event-log.md

ADR-CE-004: Signed Event Log with Deterministic Replay

Status: Accepted Date: 2026-01-22 Parent: ADR-014 Coherence Engine Architecture

Context

For audit, debugging, and compliance, the system must support:

• Complete reconstruction of any past state
• Verification that events were not tampered with
• Replay for testing and analysis

Decision

Signed event log with deterministic replay.

Every event is:

1. Assigned a monotonic sequence ID
2. Serialized with timestamp and payload
3. Signed with Blake3 hash including previous event's signature (chain)
4. Stored append-only in PostgreSQL

Replay:

• Start from genesis or checkpoint
• Apply events in sequence order
• Deterministic: same events → same state

Consequences

Benefits

• Tamper-evident: any modification breaks the hash chain
• Complete auditability: reconstruct any historical state
• Debugging: replay and inspect at any point

Risks

• Storage grows indefinitely (mitigated by checkpoints)
• Replay time scales with history length

References

• ADR-014: Coherence Engine Architecture, Section 13