fix(session-persistence): honor inspect cancellation during retirement drain

inspect() awaited an in-flight retirement drain unconditionally before entering
serialize(), so a slow drain pinned a cancelled inspect until it finished, past
the documented cancellation boundary. Race the retirement wait against the
signal with observeQueuedAbort, matching serialize()'s queued-read behaviour.
Adds a regression that cancels an inspect while a gated retirement is pending
and asserts prompt rejection without a backend read.

packages/session-persistence/session-persistence/src/coordinator.ts

@@ -282,8 +282,13 @@ export class PersistenceCoordinator<TornMarker = unknown> {
    * @returns stored header and events before any synthetic recovery closers.
    */
   inspect(id: SessionId, signal?: AbortSignal): Promise<{ meta: SessionHeader; events: SessionEvent[] }> {
-    return Promise.resolve(this.retirements.get(id))
-      .then(() => this.serialize(id, () => this.inspectCore(id, signal), signal))
+    // Waiting for an in-flight retirement drain must honor cancellation too: a
+    // slow drain would otherwise pin a cancelled inspect until it finishes,
+    // past the documented boundary. serialize() already races the signal for
+    // the queued read; do the same for the retirement wait.
+    const retired = Promise.resolve(this.retirements.get(id))
+    const waited = signal === undefined ? retired : observeQueuedAbort(retired, signal, () => false)
+    return waited.then(() => this.serialize(id, () => this.inspectCore(id, signal), signal))
   }
 
   private async inspectCore(

packages/session-persistence/session-persistence/tests/persistence.spec.ts

@@ -50,6 +50,7 @@ interface CoordinatorInternals {
   states: Map<unknown, unknown>
   live: Map<unknown, { pending: unknown[]; flush: Promise<void> | undefined }>
   chains: Map<unknown, unknown>
+  retirements: Map<unknown, Promise<void>>
 }
 
 /**
@@ -451,6 +452,53 @@ describe('PersistenceCoordinator observation cancellation', () => {
       await ctx.fiber.dispose()
     }
   })
+
+  it('rejects a cancelled inspect while an in-flight retirement drain is still pending', async () => {
+    const ctx = new Context()
+    await ctx.plugin(SessionStore)
+    const backend = new ControlledBackend()
+    let coordinator!: PersistenceCoordinator<never>
+    const backendFiber = await ctx.plugin(Object.assign((inner: Context) => {
+      coordinator = new PersistenceCoordinator(inner, backend)
+    }, { inject: ['sessions'] }))
+    const internals = coordinator as unknown as CoordinatorInternals
+    const appendGate = Promise.withResolvers<boolean>()
+    backend.beforeAppend = async () => { await appendGate.promise }
+
+    try {
+      const id = SessionId('retiring-inspect')
+      let session!: Session
+      const sessionFiber = await ctx.plugin(Object.assign((inner: Context) => {
+        session = inner.sessions.create(id)
+      }, { inject: ['sessions'] }))
+      session.append('turn/start', { turn: 1, trigger: { kind: 'message', source: { kind: 'user' } } })
+      session.append('turn/end', { turn: 1, reason: { kind: 'completed' } })
+      // Dispose the session so retirement starts; its append is gated, so the
+      // retirement promise stays pending in the coordinator.
+      await sessionFiber.dispose()
+      await vi.waitFor(() => { expect(internals.retirements.has(id)).toBe(true) })
+
+      const controller = new AbortController()
+      const reason = new Error('inspect cancelled during retirement')
+      const pending = coordinator.inspect(id, controller.signal)
+      let observedReason: unknown
+      const observed = pending.catch((error: unknown) => { observedReason = error })
+
+      // Cancel before the gated retirement can settle: the inspect must reject
+      // promptly instead of waiting for the drain, and must never reach the
+      // backend read.
+      controller.abort(reason)
+      await vi.waitFor(() => { expect(observedReason).toBe(reason) })
+      expect(backend.loadAttempts).toBe(0)
+
+      appendGate.resolve(true)
+      await observed
+    } finally {
+      appendGate.resolve(true)
+      await backendFiber.dispose()
+      await ctx.fiber.dispose()
+    }
+  })
 })
 
 describe('PersistenceCoordinator retirement', () => {