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feat(session): bound persistence write batching

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Tianyi Cui
2026-08-08 15:43:52 +08:00
parent 7ab20890e6
commit 924c954469
52 changed files with 763 additions and 126 deletions
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.agents/notes/implemented/architecture/2026-06-18-shared-persistence-write-coordinator.md
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@@ -14,7 +14,7 @@ Extract a backend-agnostic `PersistenceCoordinator` into `dsh-session-persistenc
Composition, not inheritance. The coordinator is a concrete class the backend holds, not a base class the backend extends. The Agent Note's risk — "a coordinator must not make unusual backends fight an inheritance hierarchy" — is avoided: a backend exposes only the hooks and cannot reach the coordinator's private orchestration state. A third-party backend MAY still implement the abstract service directly without the coordinator, including immutable logical inspection and the default preparation fallback through `load`.
The coordinator holds one controller for each exact live `Session`; the controller combines initialization, pending events, and the shared flush promise. Each `session/event` starts an eager drain, and `session/flush` observes quiescence rather than initiating the ordinary write path. The [flush-controller simplification](../simplification/2026-07-23-collapse-persistence-flush-state.md) owns this lifecycle.
The coordinator holds one lifecycle entry for each exact live `Session`: initialization plus a package-private write controller that owns pending events, a fixed batching deadline, the active write, failure retention, and the shared flush barrier. Each `session/event` enters that bounded write path, and `session/flush` bypasses the wait to observe quiescence. The [flush-controller simplification](../simplification/2026-07-23-collapse-persistence-flush-state.md) owns controller consolidation; the [bounded batching decision](2026-08-08-bounded-session-persistence-write-batching.md) owns scheduling cadence.
The coordinator retires a session from `session/disposed`: it waits for the controller's initialization and current flush, serializes a final drain, and removes the controller and owned per-id state only after success. A failure leaves the controller discoverable for backend teardown to retry. Settled per-id chain tails remove themselves only when they are still current, so a completion cannot erase a newer operation for the same id. Backend teardown unregisters write-path listeners, flushes every remaining controller, awaits per-id operations, and then closes the backend.
@@ -35,7 +35,7 @@ The single design choice that keeps the seam clean: the crash-repair "where is t
## Testing
The shared `runPersistenceContract` (public-API contract) runs for every backend and proves that `inspect` balances an interrupted logical view without changing storage or revisions before `prepare` or `load` commits recovery. `runCoordinatorContract` (`tests/coordinator-contract.ts`) covers adoption, HMR, collision, session and backend disposal drains, and crash-tail repair through an in-memory reference, JSONL, and SQLite. `persistence.spec.ts` and `preparations.spec.ts` cover preparation reuse and reservation, bounded prepared-state eviction, eager follow-up batches, live-controller cleanup, same-id chain-tail races, failed-drain retry, and close ordering. The per-backend specs retain storage mechanics only. A through-coordinator torn-tail repair test per real backend keeps the opaque-marker branch covered because the contract crash case produces synthetic closers without a torn marker.
The shared `runPersistenceContract` (public-API contract) runs for every backend and proves that `inspect` balances an interrupted logical view without changing storage or revisions before `prepare` or `load` commits recovery. `runCoordinatorContract` (`tests/coordinator-contract.ts`) covers adoption, HMR, collision, session and backend disposal drains, and crash-tail repair through an in-memory reference, JSONL, and SQLite. `persistence.spec.ts`, `preparations.spec.ts`, and `write-behind.spec.ts` cover preparation reuse and reservation, bounded prepared-state eviction, fixed-window follow-up batches, live-controller cleanup, same-id chain-tail races, failed-batch retry, and close ordering. The per-backend specs retain storage mechanics only. A through-coordinator torn-tail repair test per real backend keeps the opaque-marker branch covered because the contract crash case produces synthetic closers without a torn marker.
## Alternatives considered
@@ -44,4 +44,4 @@ The shared `runPersistenceContract` (public-API contract) runs for every backend
## Consequences
The coordinator adds one indirection, an opaque torn marker, detached session-retirement tasks, and bounded prepared Session state, but centralizes correctness-heavy orchestration previously duplicated by every backend. Session disposal remains an observe-only event, so the session owner does not await persistence retirement; the coordinator contains failures, preserves pending events in the live controller, and makes backend teardown the quiescence boundary. Its hook surface stays narrow: identity, adoption, collision checks, preparation, and immutable inspection reuse `loadStored`; materialization stays atomic inside `appendBatch`; and listing bypasses the coordinator. Read models use `inspect` rather than `load`, so observing a persisted open turn does not commit interruption closers; the [Session preparation decision](2026-08-05-session-preparation.md) owns reuse, reservation, and publication. New backends implement storage primitives rather than copy the eager write lifecycle.
The coordinator adds one indirection, an opaque torn marker, detached session-retirement tasks, and bounded prepared Session state, but centralizes correctness-heavy orchestration previously duplicated by every backend. Session disposal remains an observe-only event, so the session owner does not await persistence retirement; the coordinator contains failures, preserves pending events in the live controller, and makes backend teardown the quiescence boundary. Its hook surface stays narrow: identity, adoption, collision checks, preparation, and immutable inspection reuse `loadStored`; materialization stays atomic inside `appendBatch`; and listing bypasses the coordinator. Read models use `inspect` rather than `load`, so observing a persisted open turn does not commit interruption closers; the [Session preparation decision](2026-08-05-session-preparation.md) owns reuse, reservation, and publication. New backends implement storage primitives rather than copy the bounded write lifecycle.