Add event-driven daemon architecture (Phase 1 foundation)

- Add fsnotify dependency for file watching
- Create daemon_debouncer.go: batch rapid events (500ms window)
- Create daemon_watcher.go: monitor JSONL and git refs changes
- Create daemon_event_loop.go: event-driven sync loop
- Add mutation channel to RPC server (create/update/close events)
- Add BEADS_DAEMON_MODE env var (poll/events, default: poll)

Phase 1 implementation: opt-in via BEADS_DAEMON_MODE=events
Target: <500ms latency (vs 5000ms), ~60% CPU reduction

Related: bd-49 (epic), bd-50, bd-51, bd-53, bd-54, bd-55, bd-56
Amp-Thread-ID: https://ampcode.com/threads/T-35a3d0d7-4e19-421d-8392-63755035036e
Co-authored-by: Amp <amp@ampcode.com>

internal/rpc/server_core.go

@@ -46,6 +46,15 @@ type Server struct {
 	readyChan chan struct{}
 	// Auto-import single-flight guard
 	importInProgress atomic.Bool
+	// Mutation events for event-driven daemon
+	mutationChan chan MutationEvent
+}
+
+// MutationEvent represents a database mutation for event-driven sync
+type MutationEvent struct {
+	Type      string    // "create", "update", "delete", "comment"
+	IssueID   string    // e.g., "bd-42"
+	Timestamp time.Time
 }
 
 // NewServer creates a new RPC server
@@ -79,7 +88,28 @@ func NewServer(socketPath string, store storage.Storage, workspacePath string, d
 		connSemaphore:  make(chan struct{}, maxConns),
 		requestTimeout: requestTimeout,
 		readyChan:      make(chan struct{}),
+		mutationChan:   make(chan MutationEvent, 100), // Buffered to avoid blocking
 	}
 	s.lastActivityTime.Store(time.Now())
 	return s
 }
+
+// emitMutation sends a mutation event to the daemon's event-driven loop.
+// Non-blocking: drops event if channel is full (sync will happen eventually).
+func (s *Server) emitMutation(eventType, issueID string) {
+	select {
+	case s.mutationChan <- MutationEvent{
+		Type:      eventType,
+		IssueID:   issueID,
+		Timestamp: time.Now(),
+	}:
+		// Event sent successfully
+	default:
+		// Channel full, event dropped (not critical - sync will happen eventually)
+	}
+}
+
+// MutationChan returns the mutation event channel for the daemon to consume
+func (s *Server) MutationChan() <-chan MutationEvent {
+	return s.mutationChan
+}

internal/rpc/server_issues_epics.go

@@ -159,6 +159,9 @@ func (s *Server) handleCreate(req *Request) Response {
 		}
 	}
 
+	// Emit mutation event for event-driven daemon
+	s.emitMutation("create", issue.ID)
+
 	data, _ := json.Marshal(issue)
 	return Response{
 		Success: true,
@@ -190,6 +193,9 @@ func (s *Server) handleUpdate(req *Request) Response {
 		}
 	}
 
+	// Emit mutation event for event-driven daemon
+	s.emitMutation("update", updateArgs.ID)
+
 	issue, err := store.GetIssue(ctx, updateArgs.ID)
 	if err != nil {
 		return Response{
@@ -224,6 +230,9 @@ func (s *Server) handleClose(req *Request) Response {
 		}
 	}
 
+	// Emit mutation event for event-driven daemon
+	s.emitMutation("update", closeArgs.ID)
+
 	issue, _ := store.GetIssue(ctx, closeArgs.ID)
 	data, _ := json.Marshal(issue)
 	return Response{