fix(module-state): guard cancelled replication results, complete watchdog test mock

A watchdog-cancelled (or any cancelled) replication fires PouchDB's
'complete' event with no `docs` at all, crashing observePouchDbReplicate's
result parsing with `Cannot read properties of undefined (reading 'map')`.
Default to an empty array instead.

Also add the missing `removeListener` mock to the watchdog test's hung
replication stub - RxJS's teardown calls it for every event registered via
`on()`, and its absence was throwing an UnsubscriptionError that left fake
timers active and timed out the next test's afterEach hook.

Author: odinr

packages/modules/state/src/__tests__/PouchDbSyncStorage.test.ts

@@ -100,7 +100,7 @@ describe('PouchDbSyncStorage', () => {
       // the exact failure mode the watchdog exists to recover from.
       const cancel = vi.fn();
       // biome-ignore lint/suspicious/noThenProperty: mocking PouchDB's Replication, which is genuinely thenable.
-      const hungReplication = { on: vi.fn(), then: vi.fn(), cancel };
+      const hungReplication = { on: vi.fn(), removeListener: vi.fn(), then: vi.fn(), cancel };
       const replicateFrom = vi
         .spyOn(localDb.replicate, 'from')
         .mockReturnValue(hungReplication as unknown as ReturnType<typeof localDb.replicate.from>);

packages/modules/state/src/storage/observe-pouch-db-replicate.ts

@@ -29,7 +29,8 @@ export function observePouchDbReplicate<T extends AllowedValue = AllowedValue>(
   parse_docs: (doc: PouchDB.Core.ExistingDocument<{ value: T }>) => StorageItem<T>,
 ): Observable<StateSyncEventType<T>> {
   const parse_replication_result = (change: PouchDB.Replication.ReplicationResult<{ value: T }>) => ({
-    items: change.docs
+    // A cancelled (e.g. watchdog-forced) replication fires 'complete' with no `docs` at all.
+    items: (change.docs ?? [])
       // Convert replicated documents to the storage item shape expected by state events.
       .map((doc) => parse_docs(doc)),
     item_written: change.docs_written,