fix: batch cancellable title reads

packages/session-persistence/session-persistence/README.md

@@ -12,8 +12,8 @@ The persisted unit IS the existing `SessionEvent` (event-sourced model — the l
 | `create(meta): Promise<void>` | Register a new session's metadata. MAY defer the physical write until the first `append` (lazy materialization). |
 | `append(id, events): Promise<void>` | Durably persist a batch. Append-only; first event `seq` == stored next-seq after any repair; rejects non-JSON-serializable data naming the offending type. |
 | `load(id): Promise<{ meta; events }>` | Return a stored header plus a balanced contiguous log. A live load first flushes its snapshot and rejects while its turn is open; a cold load preserves an interrupted final turn and closes it with synthetic `tool/result`/`step/end?`/`turn/end {interrupted}` events. Only a torn tail fragment is dropped; committed corruption and unknown `version` reject. |
-| `inspect(id): Promise<{ meta; events }>` | Return a detached valid stored prefix without truncating a torn tail, synthesizing recovery closers, or publishing coordinator state. Serialized with same-id writes; intended for read models and other observers that must never recover a log. |
-| `list(): Promise<SessionHeader[]>` | Lightweight listing from metadata, no full-log parse. A zero-event lazily-materialized session is absent from `list`. |
+| `inspect(id, signal?): Promise<{ meta; events }>` | Return a detached valid stored prefix without truncating a torn tail, synthesizing recovery closers, or publishing coordinator state. Serialized with same-id writes; the optional signal promptly rejects a queued caller, prevents that queued backend read from starting, and cancels active backend read work. Intended for read models and other observers that must never recover a log. |
+| `list(signal?): Promise<SessionHeader[]>` | Lightweight listing from metadata, no full-log parse. The optional signal cancels backend listing work. A zero-event lazily-materialized session is absent from `list`. |
 | `listSnapshots(): Promise<SessionPersistenceSnapshot[]>` | Lightweight metadata plus an opaque branded per-log revision, without loading event logs. A revision stays equal while that log and its backing store are unchanged, changes after append or mutating load repair, and cannot collide solely because two stores use the same local counter. |
 
 ## Invariants every backend must honor
@@ -40,10 +40,10 @@ The `PersistenceBackend<TornMarker>` hooks (the only seam between the coordinato
 | Hook | Role |
 |---|---|
 | `name` | Backend label for the dispose-failure `AggregateError`. |
-| `loadStored(id)` | Read a stored prefix by id across every storage scope. Used by resume/load, non-mutating inspect, live adoption, and the create-collision probe. Returned metadata identifies `id`; an opaque `tornMarker` is present iff a torn tail must be truncated. |
+| `loadStored(id, signal?)` | Read a stored prefix by id across every storage scope. Used by resume/load, non-mutating inspect, live adoption, and the create-collision probe. The optional signal belongs to observation-only reads. Returned metadata identifies `id`; an opaque `tornMarker` is present iff a torn tail must be truncated. |
 | `appendBatch(meta, events, isMaterialized)` | Durably append a contiguous batch, lazily materializing ATOMICALLY when not yet materialized. |
 | `commitRepair(meta, tornMarker, closers)` | Make a crash repair durable: truncate the torn tail (iff `tornMarker !== undefined` — a marker may be falsy, e.g. seq/offset `0`) and append `closers`. NOT required to be atomic. Used by load (truncate + closers) and live-adoption (truncate only). |
-| `list()` | List all stored metadata. |
+| `list(signal?)` | List all stored metadata, observing optional cancellation. |
 | `close?()` | Optional lifecycle teardown (e.g. close a db handle), awaited after the dispose drain. |
 
 The coordinator asserts the stored id and compares stored/live cwd before repair or live adoption. Its `inspect()` path validates and clones the prefix without calling `commitRepair` or publishing write state. The `tornMarker` is fully OPAQUE: the coordinator only tests `!== undefined` and round-trips it to `commitRepair`, never inspecting its value (the JSONL backend uses the byte offset to truncate to, the SQLite backend the seq to delete from). A third-party backend MAY implement the abstract service directly without the coordinator, but it must provide the same non-mutating inspection and trustworthy lightweight snapshot revisions. See [the write-coordinator Agent Note](../../../.agents/notes/implemented/architecture/2026-06-18-shared-persistence-write-coordinator.md).