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-metadata.txt

@@ -0,0 +1,67 @@
+You are Worker D on the Bookshelf project (~/bookshelf). Implement BOOK METADATA
+LOOKUP + BARCODE SCANNING.
+
+FIRST, READ THESE — they are the contract, follow them exactly, do not invent
+alternative names or restate them back to me:
+  ~/bookshelf/docs/SPEC.md      (authoritative product/technical spec — see the
+                                 "Book metadata lookup" and "Barcode scanning"
+                                 sections especially)
+  ~/bookshelf/docs/HANDOFF.md   (operational state and gotchas already paid for)
+
+## Your scope — these packages ONLY, under app/app/src/main/java/org/modg/bookshelf/
+  data.metadata
+    - IsbnUtils: ISBN-13 checksum validation, ISBN-10 -> 13 conversion,
+      normalization (strip hyphens/spaces, handle trailing X)
+    - OpenLibraryClient and GoogleBooksClient (Retrofit or OkHttp + kotlinx-
+      serialization; endpoints are in SPEC)
+    - BookMetadata (source-agnostic result model) and MetadataMerger implementing
+      SPEC's merge rule: prefer whichever has a title, fill blanks from the other,
+      return null if both miss
+    - MetadataRepository: the single entry point, `suspend fun lookup(isbn): BookMetadata?`
+  ui.scan — SCANNER PLUMBING ONLY, no finished screen (wave 3 builds the screen):
+    - a CameraX ImageAnalysis analyzer wrapping ML Kit BarcodeScanning
+      (EAN_13, EAN_8, UPC_A), validating the ISBN-13 checksum before emitting,
+      debouncing repeat reads of the same code
+    - a small stateful holder exposing scan results as a Flow, plus torch toggle
+      and camera-permission-denied states
+
+## HARD BOUNDARIES — you share this repo with Worker C, running right now
+- DO NOT create or edit anything under `data.local`, `data.remote`, `data.repo`,
+  `data.prefs`, `AppContainer`, or `BookshelfApplication.kt`. Those are Worker C's.
+  Touching them WILL cause a conflict.
+- DO NOT edit any `ui.theme` or `ui.components` file — wave 1B finished those and
+  they are verified green. Reuse them; do not modify them.
+- DO NOT edit `app/build.gradle.kts` or `gradle/libs.versions.toml`. Everything
+  you need (camerax core/camera2/lifecycle/view, mlkit barcode-scanning, retrofit,
+  kotlinx-serialization, okhttp, coroutines-test, robolectric) is ALREADY declared
+  and wired. If you think something is missing, DO NOT add it — report it instead.
+- Your MetadataRepository must be a plain class with an explicit constructor
+  (e.g. taking OkHttpClient/Json). Do NOT wire it into AppContainer — Worker C owns
+  that file. In your final report, give the exact one-line wiring snippet needed.
+
+## Build/verify — CRITICAL
+Never run `./gradlew` directly; a second worker builds concurrently and you will
+corrupt each other's build. ALWAYS build with the serialized wrapper:
+    ~/bookshelf/tasks/gw assembleDebug
+    ~/bookshelf/tasks/gw testDebugUnitTest
+It takes the lock and may block until the other worker's build finishes. That is
+expected — wait for it, do not bypass it.
+
+## Definition of done — all must actually pass, verified by you, not assumed
+1. `~/bookshelf/tasks/gw assembleDebug` exits 0.
+2. `~/bookshelf/tasks/gw testDebugUnitTest` exits 0.
+3. Real unit tests with real assertions (SPEC: "Do not write assertion-free tests"):
+   - ISBN-13 checksum: known-valid and known-invalid ISBNs, ISBN-10 conversion,
+     hyphen/space handling
+   - MetadataMerger: OL-only, GB-only, both, neither(-> null), and blank-filling
+   - client JSON parsing against CHECKED-IN SAMPLE JSON FIXTURES, not live network.
+     Tests must pass offline with no network access.
+4. Network code must never be called on the main thread and must fail soft
+   (return null / empty) rather than throw on timeout or malformed JSON.
+
+## Report back (keep it short — it is read by a token-constrained orchestrator)
+- exact pass/fail of the two gradle commands above
+- files created, one line each
+- the one-line AppContainer wiring snippet for MetadataRepository
+- anything in SPEC.md you could NOT satisfy, and why. Do not paper over gaps:
+  a truthfully reported gap is worth more than a false green.