fix: Return error when all mailbox queries fail in listFromDir

Previously, listFromDir silently ignored all query errors and returned an
empty list with no error if all queries failed. This could hide real problems
like a corrupted beads database or missing bd command.

Now the function tracks whether at least one query succeeded. If all queries
fail, it returns the last error wrapped with context. This enables graceful
degradation (partial results if some queries work) while surfacing complete
failures.

(gt-lm41t)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/mail/mailbox.go

@@ -112,9 +112,12 @@ func (m *Mailbox) listBeads() ([]*Message, error) {
 // listFromDir queries messages from a beads directory.
 // Returns messages where identity is the assignee OR a CC recipient.
 // Includes both open and hooked messages (hooked = auto-assigned handoff mail).
-func (m *Mailbox) listFromDir(beadsDir string) ([]*Message, error) { //nolint:unparam // error return kept for future use
+// If all queries fail, returns the last error encountered.
+func (m *Mailbox) listFromDir(beadsDir string) ([]*Message, error) {
 	seen := make(map[string]bool)
 	var messages []*Message
+	var lastErr error
+	anySucceeded := false
 
 	// Get all identity variants to query (handles legacy vs normalized formats)
 	identities := m.identityVariants()
@@ -123,7 +126,10 @@ func (m *Mailbox) listFromDir(beadsDir string) ([]*Message, error) { //nolint:un
 	for _, identity := range identities {
 		for _, status := range []string{"open", "hooked"} {
 			msgs, err := m.queryMessages(beadsDir, "--assignee", identity, status)
-			if err == nil {
+			if err != nil {
+				lastErr = err
+			} else {
+				anySucceeded = true
 				for _, msg := range msgs {
 					if !seen[msg.ID] {
 						seen[msg.ID] = true
@@ -137,7 +143,10 @@ func (m *Mailbox) listFromDir(beadsDir string) ([]*Message, error) { //nolint:un
 	// Query for CC'd messages (open only)
 	for _, identity := range identities {
 		ccMsgs, err := m.queryMessages(beadsDir, "--label", "cc:"+identity, "open")
-		if err == nil {
+		if err != nil {
+			lastErr = err
+		} else {
+			anySucceeded = true
 			for _, msg := range ccMsgs {
 				if !seen[msg.ID] {
 					seen[msg.ID] = true
@@ -147,6 +156,11 @@ func (m *Mailbox) listFromDir(beadsDir string) ([]*Message, error) { //nolint:un
 		}
 	}
 
+	// If ALL queries failed, return the last error
+	if !anySucceeded && lastErr != nil {
+		return nil, fmt.Errorf("all mailbox queries failed: %w", lastErr)
+	}
+
 	return messages, nil
 }