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@@ -6,11 +6,11 @@ English | [中文](2026-06-18-shared-persistence-write-coordinator.zh.md)
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## Problem
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-`dsh-session-persistence-jsonl` and `dsh-session-persistence-sqlite` intentionally prove the same `SessionPersistence` contract over different storage media, but their write-path orchestration was duplicated: per-session state, `session/created` adoption, backend-specific prefix reads, write-behind control, per-id operation serialization, HMR seeding, and dispose drains. The pure seed-prefix collision and serializability guards had already moved into the Service Definition package; the remaining orchestration was still correctness-heavy and received the same fixes twice. Only the storage primitives (write bytes vs. INSERT rows) differed.
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+The JSONL provider needs correctness-heavy write orchestration around its storage primitives: per-Session state, `session/created` adoption, prefix reads, write-behind control, per-id operation serialization, HMR seeding, and dispose drains. Keeping that lifecycle in the Service Definition prevents an out-of-tree provider from copying it. The removed first-party database provider demonstrated the duplication cost; the [JSONL-only persistence decision](../simplification/2026-08-30-jsonl-only-session-persistence.md) owns its removal.
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## Decision
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-Extract a backend-agnostic `PersistenceCoordinator` into `dsh-session-persistence`. The coordinator owns the orchestration once; each first-party backend composes one (`new PersistenceCoordinator(ctx, this)`), implements a small `PersistenceBackend` hook interface, and delegates its stateful public methods (`create`/`append`/`prepare`/`load`/`inspect`/`readFrom`) to it. Backend-owned metadata and revision listing bypass the coordinator.
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+`dsh-session-persistence` exports a backend-agnostic `PersistenceCoordinator`. The JSONL provider composes one (`new PersistenceCoordinator(ctx, this)`), implements the small `PersistenceBackend` hook interface, and delegates its stateful public methods (`create`/`append`/`prepare`/`load`/`inspect`/`readFrom`) to it. Backend-owned metadata and revision listing bypass the coordinator.
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Composition, not inheritance. The coordinator is a concrete class the backend holds, not a base class the backend extends. The risk that a coordinator makes 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`.
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@@ -27,26 +27,26 @@ The coordinator retires a session from `session/disposed`: it waits for the cont
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Five required members plus optional empty-materialization and lifecycle hooks form the only boundary between the coordinator and storage:
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- `name` — backend label for the dispose-failure `AggregateError`.
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-- `loadStored(id)` — read one stored prefix by id across every storage scope (every JSONL project directory; SQLite's id is globally unique). Preparation, logical load/inspection, physical suffix reads, live adoption, and the create-collision probe share this lookup. The coordinator asserts the returned id and rejects a stored/live cwd mismatch before repair or state publication.
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+- `loadStored(id)` — read one stored prefix by id across every storage scope. Preparation, logical load/inspection, physical suffix reads, live adoption, and the create-collision probe share this lookup. The coordinator asserts the returned id and rejects a stored/live cwd mismatch before repair or state publication.
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- `appendBatch(meta, events, isMaterialized)` — durably append a contiguous batch, lazily materializing the session ATOMICALLY when not yet materialized. Ordinary creation therefore cannot leave an abandoned materialized-but-empty session.
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- `materializeHeader?(meta)` — explicitly persist a header-only session for `SessionPersistence.ensureMaterialized(session)`. This is reserved for a lifecycle frontend that treats an empty session itself as a resumable durable resource; [standard ACP automation controls](../feature/2026-08-22-standard-acp-automation-controls.md) are the first consumer. Backends that support that lifecycle implement the hook; lazy creation remains the default.
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-- `commitRepair(meta, tornMarker, closers)` — make a crash repair durable: truncate the torn tail (iff `tornMarker !== undefined`) and append `closers`. **NOT required to be atomic** — JSONL legitimately truncates-then-appends in two fsync'd steps, SQLite does DELETE+INSERT in one transaction. Used by `prepare`/`load` (truncate + synthetic closers) and live-adoption (truncate only, `closers = []`).
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+- `commitRepair(meta, tornMarker, closers)` — make a crash repair durable: truncate the torn tail (iff `tornMarker !== undefined`) and append `closers`. **NOT required to be atomic** — JSONL legitimately truncates then appends in two fsync'd steps. Used by `prepare`/`load` (truncate + synthetic closers) and live adoption (truncate only, `closers = []`).
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- `list()` — list all stored metadata.
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-- `close?()` — optional lifecycle teardown (SQLite closes its db handle; JSONL omits it), awaited in the dispose effect AFTER the quiescence drain so a close failure never masks a drain error.
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+- `close?()` — optional lifecycle teardown for a provider with owned resources; JSONL omits it. The dispose effect awaits it after the quiescence drain so a close failure never masks a drain error.
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### The opaque torn marker
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-The single design choice that keeps the seam clean: the crash-repair "where is the torn tail" token is OPAQUE to the coordinator. The coordinator computes the synthetic closers (it owns `interruptedTurnClosers` from `dsh-session`), but it only ever tests `tornMarker !== undefined` and passes the value straight back to `commitRepair` — it never inspects it. Each backend picks its own marker type: JSONL carries the byte offset to truncate to plus any complete events decoded from an incomplete final frame, while SQLite carries the seq to delete from. The coordinator therefore knows neither byte lengths nor frame recovery state.
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+The single design choice that keeps the seam clean: the crash-repair "where is the torn tail" token is opaque to the coordinator. The coordinator computes the synthetic closers (it owns `interruptedTurnClosers` from `dsh-session`), but it only tests `tornMarker !== undefined` and passes the value straight back to `commitRepair`; it never inspects it. JSONL carries the byte offset to truncate to plus any complete events decoded from an incomplete final frame, while another provider may choose its own marker type. The coordinator therefore knows neither byte lengths nor frame recovery state.
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## Testing
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-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.
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+The shared `runPersistenceContract` proves that JSONL `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 provider disposal drains, and crash-tail repair through an in-memory reference and JSONL. `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. JSONL specs retain storage mechanics and the through-coordinator torn-tail case that exercises the opaque-marker branch.
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## Alternatives considered
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- **A base class the backends extend** — rejected for composition: a backend exposes only the hooks, cannot reach the coordinator's private orchestration state, and a third-party backend may still implement the abstract service directly without the coordinator at all.
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-- **A wider hook API** — each candidate hook folds away: there is no scope-specific live lookup because `loadStored` plus the coordinator's cwd check preserves the collision boundary, no storage-locator generic because validated JSONL metadata reproduces its path while SQLite is already id-bound, no separate `materialize` hook because the first batch must commit atomically with materialization, no separate create-collision probe because it is `loadStored(id) !== undefined`, and no coordinator pass-through for `list()` because listing needs none of the orchestration.
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+- **A wider hook API** — each candidate hook folds away: there is no scope-specific live lookup because `loadStored` plus the coordinator's cwd check preserves the collision boundary, no storage-locator generic because validated JSONL metadata reproduces its path, no separate `materialize` hook because the first batch must commit atomically with materialization, no separate create-collision probe because it is `loadStored(id) !== undefined`, and no coordinator pass-through for `list()` because listing needs none of the orchestration.
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## Consequences
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-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.
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+The coordinator adds one indirection, an opaque torn marker, detached Session-retirement tasks, and bounded prepared Session state, but centralizes correctness-heavy orchestration for the JSONL provider and future implementations. 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 provider 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. A new provider implements storage primitives rather than copy the bounded write lifecycle.
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