Fix bd-373c: Surface daemon errors when multiple .db files exist

When daemon detects multiple .db files (after filtering .backup and vc.db),
it now writes detailed error to .beads/daemon-error file before exiting.

The error file is checked and displayed when:
- Daemon discovery fails to connect
- Auto-start fails to yield a running daemon
- User runs 'bd daemons list'

This makes the error immediately visible without requiring users to check
daemon logs.

Changes:
- cmd/bd/daemon.go: Write daemon-error file on multiple .db detection
- internal/daemon/discovery.go: Read and surface daemon-error in DaemonInfo.Error
- cmd/bd/main.go: Display daemon-error when auto-start fails

Amp-Thread-ID: https://ampcode.com/threads/T-1005a8d1-7a5a-4844-ad2d-2b8a6145825f
Co-authored-by: Amp <amp@ampcode.com>

cmd/bd/daemon.go

@@ -1371,13 +1371,22 @@ func runDaemonLoop(interval time.Duration, autoCommit, autoPush bool, logPath, p
 			}
 		}
 		if len(validDBs) > 1 {
-			log.log("Error: Multiple database files found in %s:", beadsDir)
+			errMsg := fmt.Sprintf("Error: Multiple database files found in %s:\n", beadsDir)
 			for _, db := range validDBs {
-				log.log("  - %s", filepath.Base(db))
+				errMsg += fmt.Sprintf("  - %s\n", filepath.Base(db))
 			}
-			log.log("")
-			log.log("Beads requires a single canonical database: %s", beads.CanonicalDatabaseName)
-			log.log("Run 'bd init' to migrate legacy databases or manually remove old databases")
+			errMsg += fmt.Sprintf("\nBeads requires a single canonical database: %s\n", beads.CanonicalDatabaseName)
+			errMsg += "Run 'bd init' to migrate legacy databases or manually remove old databases\n"
+			errMsg += "Or run 'bd doctor' for more diagnostics"
+			
+			log.log(errMsg)
+			
+			// Write error to file so user can see it without checking logs
+			errFile := filepath.Join(beadsDir, "daemon-error")
+			if err := os.WriteFile(errFile, []byte(errMsg), 0644); err != nil {
+				log.log("Warning: could not write daemon-error file: %v", err)
+			}
+			
 			os.Exit(1)
 		}
 	}
@@ -1394,6 +1403,12 @@ func runDaemonLoop(interval time.Duration, autoCommit, autoPush bool, logPath, p
 
 	log.log("Using database: %s", daemonDBPath)
 
+	// Clear any previous daemon-error file on successful startup
+	errFile := filepath.Join(beadsDir, "daemon-error")
+	if err := os.Remove(errFile); err != nil && !os.IsNotExist(err) {
+		log.log("Warning: could not remove daemon-error file: %v", err)
+	}
+
 	store, err := sqlite.New(daemonDBPath)
 	if err != nil {
 		log.log("Error: cannot open database: %v", err)

cmd/bd/main.go

@@ -370,6 +370,14 @@ var rootCmd = &cobra.Command{
 						if err != nil {
 							daemonStatus.Detail = err.Error()
 						}
+						// Check for daemon-error file to provide better error message
+						if beadsDir := filepath.Dir(socketPath); beadsDir != "" {
+							errFile := filepath.Join(beadsDir, "daemon-error")
+							if errMsg, readErr := os.ReadFile(errFile); readErr == nil && len(errMsg) > 0 {
+								fmt.Fprintf(os.Stderr, "\n%s\n", string(errMsg))
+								daemonStatus.Detail = string(errMsg)
+							}
+						}
 						if os.Getenv("BD_DEBUG") != "" {
 							fmt.Fprintf(os.Stderr, "Debug: auto-start did not yield a running daemon; falling back to direct mode\n")
 						}

internal/daemon/discovery.go

@@ -149,10 +149,18 @@ func discoverDaemon(socketPath string) DaemonInfo {
 	client, err := rpc.TryConnectWithTimeout(socketPath, 500*time.Millisecond)
 	if err != nil {
 		daemon.Error = fmt.Sprintf("failed to connect: %v", err)
+		// Check for daemon-error file
+		if errMsg := checkDaemonErrorFile(socketPath); errMsg != "" {
+			daemon.Error = errMsg
+		}
 		return daemon
 	}
 	if client == nil {
 		daemon.Error = "daemon not responding or unhealthy"
+		// Check for daemon-error file
+		if errMsg := checkDaemonErrorFile(socketPath); errMsg != "" {
+			daemon.Error = errMsg
+		}
 		return daemon
 	}
 	defer client.Close()
@@ -204,6 +212,20 @@ func FindDaemonByWorkspace(workspacePath string) (*DaemonInfo, error) {
 	return nil, fmt.Errorf("no daemon found for workspace: %s", workspacePath)
 }
 
+// checkDaemonErrorFile checks for a daemon-error file in the .beads directory
+func checkDaemonErrorFile(socketPath string) string {
+	// Socket path is typically .beads/bd.sock, so get the parent dir
+	beadsDir := filepath.Dir(socketPath)
+	errFile := filepath.Join(beadsDir, "daemon-error")
+	
+	data, err := os.ReadFile(errFile)
+	if err != nil {
+		return ""
+	}
+	
+	return string(data)
+}
+
 // CleanupStaleSockets removes socket files and PID files for dead daemons
 func CleanupStaleSockets(daemons []DaemonInfo) (int, error) {
 	cleaned := 0