fix: Fix daemon export leaving JSONL newer than database (issues #301, #321)

After daemon auto-export, JSONL mtime could be newer than database mtime
due to SQLite WAL mode not updating beads.db until checkpoint. This caused
validatePreExport to incorrectly block subsequent exports with "JSONL is
newer than database" error, leading to daemon shutdown.

Solution: Call TouchDatabaseFile after all export operations to ensure
database mtime >= JSONL mtime. This prevents false positives in validation

cmd/bd/sync.go

@@ -590,6 +590,15 @@ func exportToJSONL(ctx context.Context, jsonlPath string) error {
 	// Clear auto-flush state
 	clearAutoFlushState()
 
+	// Update database mtime to be >= JSONL mtime (fixes #278, #301, #321)
+	// This prevents validatePreExport from incorrectly blocking on next export
+	beadsDir := filepath.Dir(jsonlPath)
+	dbPath := filepath.Join(beadsDir, "beads.db")
+	if err := TouchDatabaseFile(dbPath, jsonlPath); err != nil {
+		// Non-fatal warning
+		fmt.Fprintf(os.Stderr, "Warning: failed to update database mtime: %v\n", err)
+	}
+
 	return nil
 }