Fix bd-66: Add robust polling fallback for file watcher

- Detect fsnotify.NewWatcher() errors and auto-fallback to polling mode
- Add BEADS_WATCHER_FALLBACK env var to control behavior (default: enabled)
- Poll every 5 seconds with comprehensive change detection:
  - Track file existence, size, and mtime to catch all changes
  - Handle file disappearance/reappearance correctly
  - Trigger on file recreation even with older timestamps
- Fix goroutine leak: Close() now stops background goroutines via cancel context
- Tighten git refs filtering to only trigger for events under .git/refs/heads
- Trigger after successful JSONL rewatch on rename/remove events
- Improve logging to show actual poll interval in warnings

All tests passing.

Amp-Thread-ID: https://ampcode.com/threads/T-8f5edc23-4b78-4b80-b8f3-66050f45eb61
Co-authored-by: Amp <amp@ampcode.com>

.beads/beads.jsonl

@@ -62,7 +62,7 @@
 {"id":"bd-63","title":"Add internal/ai package for LLM integration","description":"Shared AI client for repair commands.\n\nProviders:\n- Anthropic (Claude)\n- OpenAI (GPT)\n- Ollama (local)\n\nEnv vars:\n- BEADS_AI_PROVIDER\n- BEADS_AI_API_KEY\n- BEADS_AI_MODEL\n\nFiles: internal/ai/client.go (new)","status":"open","priority":1,"issue_type":"task","created_at":"2025-10-28T14:48:29.072473-07:00","updated_at":"2025-10-28T14:48:29.072473-07:00","dependencies":[{"issue_id":"bd-63","depends_on_id":"bd-56","type":"blocks","created_at":"2025-10-28T14:48:29.073553-07:00","created_by":"daemon"}]}
 {"id":"bd-64","title":"Add embedding generation for duplicate detection","description":"Use embeddings for scalable duplicate detection.\n\nModel: text-embedding-3-small (OpenAI) or all-MiniLM-L6-v2 (local)\nStorage: SQLite vector extension or in-memory\nCost: ~/bin/bash.0002 per 100 issues\n\nMuch cheaper than LLM comparisons for large databases.\n\nFiles: internal/embeddings/ (new package)","status":"open","priority":2,"issue_type":"task","created_at":"2025-10-28T14:48:29.072913-07:00","updated_at":"2025-10-28T14:48:29.072913-07:00","dependencies":[{"issue_id":"bd-64","depends_on_id":"bd-56","type":"blocks","created_at":"2025-10-28T14:48:29.07486-07:00","created_by":"daemon"}]}
 {"id":"bd-65","title":"bd resolve-conflicts - Git merge conflict resolver","description":"Automatically resolve JSONL merge conflicts.\n\nModes:\n- Mechanical: ID remapping (no AI)\n- AI-assisted: Smart merge/keep decisions\n- Interactive: Review each conflict\n\nHandles \u003c\u003c\u003c\u003c\u003c\u003c\u003c conflict markers in .beads/beads.jsonl\n\nFiles: cmd/bd/resolve_conflicts.go (new)","status":"open","priority":1,"issue_type":"task","created_at":"2025-10-28T14:48:30.083642-07:00","updated_at":"2025-10-28T14:48:30.083642-07:00","dependencies":[{"issue_id":"bd-65","depends_on_id":"bd-56","type":"blocks","created_at":"2025-10-28T14:48:30.084575-07:00","created_by":"daemon"}]}
-{"id":"bd-66","title":"Add fallback to polling on watcher failure","description":"Detect fsnotify.NewWatcher() errors and log warning. Auto-switch to polling mode with 5s ticker. Add BEADS_WATCHER_FALLBACK env var to control behavior.","status":"open","priority":1,"issue_type":"task","created_at":"2025-10-28T16:20:02.428439-07:00","updated_at":"2025-10-28T16:20:02.428439-07:00"}
+{"id":"bd-66","title":"Add fallback to polling on watcher failure","description":"Detect fsnotify.NewWatcher() errors and log warning. Auto-switch to polling mode with 5s ticker. Add BEADS_WATCHER_FALLBACK env var to control behavior.","status":"closed","priority":1,"issue_type":"task","created_at":"2025-10-28T16:20:02.428439-07:00","updated_at":"2025-10-28T19:23:43.595916-07:00","closed_at":"2025-10-28T19:23:43.595916-07:00"}
 {"id":"bd-67","title":"Create cmd/bd/daemon_event_loop.go (~200 LOC)","description":"Implement runEventDrivenLoop to replace polling ticker. Coordinate FileWatcher, mutation events, debouncer. Include health check ticker (60s) for daemon validation.","status":"closed","priority":1,"issue_type":"task","created_at":"2025-10-28T16:20:02.429383-07:00","updated_at":"2025-10-28T16:20:02.429383-07:00","closed_at":"2025-10-28T12:30:44.067036-07:00"}
 {"id":"bd-68","title":"Add fsnotify dependency to go.mod","description":"","status":"in_progress","priority":1,"issue_type":"task","created_at":"2025-10-28T16:20:02.429763-07:00","updated_at":"2025-10-28T16:20:02.429763-07:00"}
 {"id":"bd-69","title":"Replace getStorageForRequest with Direct Access","description":"Replace all getStorageForRequest(req) calls with s.storage","acceptance_criteria":"- No references to getStorageForRequest() in codebase (except in deleted file)\n- All handlers use s.storage directly\n- Code compiles without errors\n\nFiles to update:\n- internal/rpc/server_issues_epics.go (~8 calls)\n- internal/rpc/server_labels_deps_comments.go (~4 calls)\n- internal/rpc/server_compact.go (~2 calls)\n- internal/rpc/server_export_import_auto.go (~2 calls)\n- internal/rpc/server_routing_validation_diagnostics.go (~1 call)\n\nPattern: store, err := s.getStorageForRequest(req) → store := s.storage","status":"closed","priority":1,"issue_type":"task","created_at":"2025-10-28T16:20:02.430127-07:00","updated_at":"2025-10-28T19:20:58.312809-07:00","closed_at":"2025-10-28T19:20:58.312809-07:00"}