refactor: eliminate mock.module() with DI, simplify test scripts

[rjroy]

Summary

• Replace all mock.module() calls with dependency injection pattern across backend test files
• All 2,667 backend tests now run together in a single process (~11s)
• Simplified test scripts: bun test and bun test --coverage

Changes

Phase 1: Sync Modules DI

• Add SyncPipelineManagerDependencies interface for connector and normalizer injection
• Update sync-pipeline.test.ts, sync-integration.test.ts, sync-handlers.test.ts

Phase 2: Session Manager DI

• Add QueryFunction type and parameter to session functions
• Update session-manager.test.ts to inject mock query function

Phase 3: File Watcher DI

• Add FileWatcherDependencies interface for chokidar watch and fs readFile
• Update file-watcher.test.ts to inject mock deps
• Fix chokidar v5.0.0 type changes (WatchOptions → ChokidarOptions)

Phase 4: WebSocket Handler DI

• Add WebSocketHandlerDependencies interface to websocket-handler.ts
• Create createTestHandler() wrapper for consistent mock injection
• Update all 100+ test instantiations to use DI mocks

Phase 5: Handler Dependencies DI (completes the work)

• Add HandlerDependencies interface to handlers/types.ts
• Handler functions receive deps via ctx.deps instead of direct imports
• Add isFileBrowserError() helper to avoid instanceof checks on mocked classes
• Add createSearchIndex factory to WebSocketHandlerDependencies
• Update handlers: home-handlers, browser-handlers, widget-handlers
• Remove all 8 remaining mock.module() calls from websocket-handler.test.ts

Test Script Simplification

{
  "test": "LOG_LEVEL=silent bun test",
  "test:coverage": "LOG_LEVEL=silent bun test --coverage"
}

Removed all test:batch* commands - no longer needed.

Test plan

• All 2,667 backend tests pass in single run
• All 1,099 frontend tests pass
• All 425 shared tests pass
• Pre-commit hook passes (typecheck, lint, unit tests)
• Coverage collection works with simplified script

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 96.68508% with 6 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
backend/src/handlers/browser-handlers.ts	81.81%	2 Missing ⚠️
backend/src/websocket-handler.ts	97.91%	2 Missing ⚠️
backend/src/handlers/home-handlers.ts	90.90%	1 Missing ⚠️
backend/src/handlers/widget-handlers.ts	80.00%	1 Missing ⚠️

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