Status: implemented
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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).
A Session is an append-only log of typed SessionEvents — 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 claims inbox messages before agent/pre-step, opens step/start only after an enter decision, then appends the returned user/message batch before request derivation. Provider output is assembled and appended as assistant/message before tool dispatch, so the durable log records the exact message the tools follow. Regression tests pin that ordering.
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.
- 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 froze its shape once the log became durable.
- Derivation cost grows with log length — compaction (dsh-compaction) is the intended mitigation, not log mutation.