Tianyi Cui
27 lines
1.8 KiB
Markdown
27 lines
1.8 KiB
Markdown
# RFC: Event-sourced sessions with derived message history
|
|
|
|
Status: implemented
|
|
|
|
## Problem
|
|
|
|
The MVP requires strict event-based tracing with fully replayable sessions (严格的基于事件的trace、logging系统，session完全可回放).
|
|
|
|
## Decision
|
|
|
|
A `Session` is an append-only log of typed `SessionEvent`s — the single source of truth. The LLM message history is *derived* from the log (`deriveMessages()`); raw stream chunks are logged for token-level replay fidelity while the assembled `assistant/message` event is authoritative for derivation. Replay/fork = seed a new session with an existing log.
|
|
|
|
Appends are synchronous (the hot path never blocks on I/O); `session/event` is a sync notification; persistence plugins buffer write-behind and drain at the awaited `session/flush` checkpoint fired at every turn end.
|
|
|
|
Ordering contract: the loop appends to the session *before* emitting the corresponding Cordis event, and the `agent/step-result` waterfall runs before the `assistant/message` append so the log records the message tool dispatch actually used. Regression tests pin that ordering.
|
|
|
|
## Alternatives considered
|
|
|
|
**A mutable message array with events fired as notifications** — simpler, but state and log can diverge; with event-sourcing the log IS the state, so divergence is structurally impossible.
|
|
|
|
## Consequences
|
|
|
|
- Replay, trace, and telemetry are structurally guaranteed, not bolted on.
|
|
- Persistence stays a plugin concern; the in-memory store ships in dsh-session.
|
|
- The event vocabulary is merge-extensible (plugins add e.g. compaction events); [session persistence](2026-06-14-session-persistence.md) froze its shape once the log became durable.
|
|
- Derivation cost grows with log length — compaction (future plugin) is the intended mitigation, not log mutation.
|