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.