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/C-data.txt

@@ -0,0 +1,53 @@
+You are Worker C on the Bookshelf project (~/bookshelf). Implement the DATA LAYER.
+
+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)
+  ~/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.local   Room: BookEntity/BookcaseEntity/ShelfEntity, SyncState, Converters,
+               BookDao/BookcaseDao/ShelfDao, BookshelfDatabase
+  data.remote  PocketBaseApi (Retrofit), request/response DTOs, PbAuthInterceptor
+  data.repo    BookRepository, LocationRepository, AuthRepository, SyncEngine
+  data.prefs   SettingsStore (DataStore: server URL, auth token, per-collection
+               sync cursors, last-sync time)
+  Plus `AppContainer` (manual DI, per SPEC "NO Hilt/kapt") and its wiring into
+  the existing BookshelfApplication.kt.
+
+## HARD BOUNDARIES — you share this repo with Worker D, running right now
+- DO NOT create or edit anything under `data.metadata`, `ui.scan`, or any `ui.*`
+  package. Those are Worker D's / wave 3's. Touching them WILL cause a conflict.
+- DO NOT edit `app/build.gradle.kts` or `gradle/libs.versions.toml`. Every
+  dependency you need (room+ksp, retrofit, kotlinx-serialization, okhttp,
+  datastore, work-runtime, robolectric, coroutines-test) is ALREADY declared and
+  wired. If you genuinely believe something is missing, DO NOT add it — say so in
+  your final report and work around it.
+- Worker D will need metadata lookup reachable from AppContainer. Do NOT try to
+  wire it. Just leave AppContainer easy to extend; D exposes a plain class that
+  gets wired later.
+
+## 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"):
+   - SyncEngine conflict resolution / last-write-wins on `updated`
+   - push ordering + syncState transitions, incl. 404-on-update -> drop local,
+     409/duplicate-id -> switch to PATCH
+   - client-side 15-char lowercase-alnum id generation
+   - DAO queries via Robolectric, proving `deleted = 0` filtering works
+4. Soft delete everywhere. All reads come from Room. Nothing blocks on network.
+
+## 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
+- 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.