perf(service): construct RustInterface off the main thread

[0xbrayo]

Part of #333.

BackgroundService.onCreate constructed RustInterface on the main thread. Construction runs System.loadLibrary("aw_server") plus the JNI initialize / setDataDir, which the code's own comment notes "can take several seconds on slow/no-KVM emulators". #262 moved exactly this off the main thread for the watchers, MainActivity and the alarm receiver; the service was the remaining caller.

Change

• rustInterface is now an OffThreadInit<RustInterface> started in onCreate, after foreground promotion as before.
• Its three users (server start, hostname migration, watcher-bucket migration) already run on IO coroutines and now await() it there.
• The server-start coroutine awaits before taking sanitizedMigrationLock. Construction doesn't open the database, so it doesn't need to be ordered against the hostname rewrite.
• If the native library fails to load, that is logged and the dependent work is skipped, instead of crashing the service in onCreate.

Testing

• ./gradlew :mobile:testStandardDebugUnitTest passes, including BackgroundServicePolicyTest and OffThreadInitTest.

[greptile-apps]

Confidence Score: 5/5

[Medium impact] This PR appears safe to merge.

Summary

Moves RustInterface construction off the main thread in BackgroundService.

• Server startup and both native migrations await initialization on IO coroutines.
• Server startup keeps the existing migration lock and shutdown check.
• 0xbrayo explicitly intends initialization failures to be logged and dependent work skipped.
• No actionable issues found. Tests were inspected, not run.

Diagram

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A["onCreate: enter foreground"] --> B["Start BackgroundService-init thread"]
    B --> C["Construct RustInterface"]
    A --> D["onStartCommand: prepare dashboard key"]
    D --> E["IO: await initialization"]
    D --> F["IO: await initialization"]
    C --> E
    C --> F
    E --> G["Take sanitizedMigrationLock"]
    G --> H{"Service destroyed?"}
    H -->|No| I["Rewrite hostname, then start server"]
    H -->|Yes| J["Skip server startup"]
    F --> K["Migrate hostname, then watcher buckets"]
    C -->|Failure| L["Log and skip dependent work"]

Loading

_{Reviews (1) · Last reviewed commit: "perf(service): construct RustInterface o..." · Reviewed by Greptile}