feat: add gt mail check command and update prime for GGT cutover

- Add 'gt mail check' with --inject flag for Claude Code hooks
- Update Mayor prime output to include mail commands and startup info
- Enables full cutover from PGT 'town' commands to GGT 'gt' commands

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

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

internal/cmd/mail.go

@@ -22,6 +22,8 @@ var (
 	mailInboxJSON   bool
 	mailReadJSON    bool
 	mailInboxUnread bool
+	mailCheckInject bool
+	mailCheckJSON   bool
 )
 
 var mailCmd = &cobra.Command{
@@ -87,6 +89,25 @@ This closes the message in beads.`,
 	RunE: runMailDelete,
 }
 
+var mailCheckCmd = &cobra.Command{
+	Use:   "check",
+	Short: "Check for new mail (for hooks)",
+	Long: `Check for new mail - useful for Claude Code hooks.
+
+Exit codes (normal mode):
+  0 - New mail available
+  1 - No new mail
+
+Exit codes (--inject mode):
+  0 - Always (hooks should never block)
+  Output: system-reminder if mail exists, silent if no mail
+
+Examples:
+  gt mail check             # Simple check
+  gt mail check --inject    # For hooks`,
+	RunE: runMailCheck,
+}
+
 func init() {
 	// Send flags
 	mailSendCmd.Flags().StringVarP(&mailSubject, "subject", "s", "", "Message subject (required)")
@@ -102,11 +123,16 @@ func init() {
 	// Read flags
 	mailReadCmd.Flags().BoolVar(&mailReadJSON, "json", false, "Output as JSON")
 
+	// Check flags
+	mailCheckCmd.Flags().BoolVar(&mailCheckInject, "inject", false, "Output format for Claude Code hooks")
+	mailCheckCmd.Flags().BoolVar(&mailCheckJSON, "json", false, "Output as JSON")
+
 	// Add subcommands
 	mailCmd.AddCommand(mailSendCmd)
 	mailCmd.AddCommand(mailInboxCmd)
 	mailCmd.AddCommand(mailReadCmd)
 	mailCmd.AddCommand(mailDeleteCmd)
+	mailCmd.AddCommand(mailCheckCmd)
 
 	rootCmd.AddCommand(mailCmd)
 }
@@ -363,3 +389,81 @@ func detectSender() string {
 	// Default to mayor
 	return "mayor/"
 }
+
+func runMailCheck(cmd *cobra.Command, args []string) error {
+	// Find workspace
+	workDir, err := findBeadsWorkDir()
+	if err != nil {
+		if mailCheckInject {
+			// Inject mode: always exit 0, silent on error
+			return nil
+		}
+		return fmt.Errorf("not in a Gas Town workspace: %w", err)
+	}
+
+	// Determine which inbox
+	address := detectSender()
+
+	// Get mailbox
+	router := mail.NewRouter(workDir)
+	mailbox, err := router.GetMailbox(address)
+	if err != nil {
+		if mailCheckInject {
+			return nil
+		}
+		return fmt.Errorf("getting mailbox: %w", err)
+	}
+
+	// Count unread
+	_, unread, err := mailbox.Count()
+	if err != nil {
+		if mailCheckInject {
+			return nil
+		}
+		return fmt.Errorf("counting messages: %w", err)
+	}
+
+	// JSON output
+	if mailCheckJSON {
+		result := map[string]interface{}{
+			"address": address,
+			"unread":  unread,
+			"has_new": unread > 0,
+		}
+		enc := json.NewEncoder(os.Stdout)
+		enc.SetIndent("", "  ")
+		return enc.Encode(result)
+	}
+
+	// Inject mode: output system-reminder if mail exists
+	if mailCheckInject {
+		if unread > 0 {
+			// Get subjects for context
+			messages, _ := mailbox.ListUnread()
+			var subjects []string
+			for _, msg := range messages {
+				subjects = append(subjects, fmt.Sprintf("- From %s: %s", msg.From, msg.Subject))
+			}
+
+			fmt.Println("<system-reminder>")
+			fmt.Printf("You have %d unread message(s) in your inbox.\n\n", unread)
+			for _, s := range subjects {
+				fmt.Println(s)
+			}
+			fmt.Println()
+			fmt.Println("Run 'gt mail inbox' to see your messages, or 'gt mail read <id>' for a specific message.")
+			fmt.Println("</system-reminder>")
+		}
+		return nil
+	}
+
+	// Normal mode
+	if unread > 0 {
+		fmt.Printf("%s %d unread message(s)\n", style.Bold.Render("📬"), unread)
+		os.Exit(0)
+	} else {
+		fmt.Println("No new mail")
+		os.Exit(1)
+	}
+	return nil
+}

internal/cmd/prime.go

@@ -156,10 +156,15 @@ func outputMayorContext(ctx RoleContext) {
 	fmt.Println("- Monitor overall system health")
 	fmt.Println()
 	fmt.Println("## Key Commands")
+	fmt.Println("- `gt mail inbox` - Check your messages")
+	fmt.Println("- `gt mail read <id>` - Read a specific message")
 	fmt.Println("- `gt status` - Show overall town status")
 	fmt.Println("- `gt rigs` - List all rigs")
 	fmt.Println("- `bd ready` - Issues ready to work")
 	fmt.Println()
+	fmt.Println("## Startup")
+	fmt.Println("Check for handoff messages with 🤝 HANDOFF in subject - continue predecessor's work.")
+	fmt.Println()
 	fmt.Printf("Town root: %s\n", style.Dim.Render(ctx.TownRoot))
 }