Wave 2: data layer (C) + metadata/scanning (D)

Room entities/DAOs/DB, PocketBase Retrofit client + auth interceptor, SyncEngine
(push-then-pull, LWW, tombstones, client-generated ids), SettingsStore, AppContainer.
Open Library + Google Books merge, ISBN validation, CameraX + ML Kit scanner plumbing.

Verified by orchestrator: assembleDebug exit 0; testDebugUnitTest exit 0, 68 tests,
0 failures, 0 errors.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016bThmkmyUUdqQpy3MXFFe5

tasks/D-fix.txt

@@ -0,0 +1,32 @@
+Your wave-2 work is mostly good and `assembleDebug` passes. But you ended your turn
+reporting that `testDebugUnitTest` was "running in background, will report once it
+completes" — you never confirmed it. The orchestrator ran it. IT FAILS.
+
+68 tests ran, 2 failed, both yours, both in
+`app/app/src/test/java/org/modg/bookshelf/ui/scan/ScannerControllerTest.kt`:
+
+  ScannerControllerTest > "valid barcode emits on scanResults"
+  ScannerControllerTest > "invalid barcode does not reach scanResults"
+  both: kotlinx.coroutines.test.UncompletedCoroutinesError:
+        After waiting for 1m, the test body did not run to completion
+
+Diagnosis (confirm it yourself before acting): `ScannerController._scanResults` is a
+`MutableSharedFlow<String>(extraBufferCapacity = 1)` with NO `replay`. Both tests call
+`onBarcodeScanned(...)` BEFORE anything subscribes, so with replay=0 the emission goes
+nowhere, and the later `scanResults.first()` suspends forever until runTest's timeout.
+
+Fix the TEST, not the production semantics, unless you have a concrete reason to do
+otherwise. replay=0 is correct for a barcode scanner — a newly-attached collector must
+not receive a stale scan from earlier. So make the test subscribe BEFORE emitting, e.g.
+start the collector with `async`/`backgroundScope`, use `runCurrent()` to let it
+subscribe, then call `onBarcodeScanned(...)`. Keep both tests' original intent intact:
+the second one must still prove the invalid barcode is filtered out and only the valid
+ISBN arrives. Do not weaken a test into an assertion-free or trivially-true test, and
+do not delete a test to make the suite green.
+
+Then VERIFY, and this time actually wait for the result before you answer:
+    ~/bookshelf/tasks/gw testDebugUnitTest
+(use that wrapper, never ./gradlew directly). It must exit 0 with 0 failures.
+
+Reply with: the command's real exit code, the failure count, and one line on what you
+changed. Nothing else.