feat(gate): add add-waiter and show commands for phase handoff

- Add `bd gate add-waiter <gate-id> <waiter>` command to register
  agents as waiters on a gate bead using the native Waiters field
- Add `bd gate show <gate-id>` command to display gate details
  including waiters (used by gt gate wake)
- Add Waiters field to UpdateArgs in RPC protocol
- Update server to handle waiters field in updates

This is part of the polecat phase handoff feature (bd-quw1).
The corresponding gastown changes (gt done --phase-complete) are
tracked separately.

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

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

cmd/bd/gate.go

@@ -167,6 +167,175 @@ func displayGates(gates []*types.Issue) {
 	fmt.Printf("To resolve a gate: bd close <gate-id>\n")
 }
 
+// gateAddWaiterCmd adds a waiter to a gate
+var gateAddWaiterCmd = &cobra.Command{
+	Use:   "add-waiter <gate-id> <waiter>",
+	Short: "Add a waiter to a gate",
+	Long: `Register an agent as a waiter on a gate bead.
+
+When the gate closes, the waiter will receive a wake notification via 'gt gate wake'.
+The waiter is typically the polecat's address (e.g., "gastown/polecats/Toast").
+
+This is used by 'gt done --phase-complete' to register for gate wake notifications.`,
+	Args: cobra.ExactArgs(2),
+	Run: func(cmd *cobra.Command, args []string) {
+		CheckReadonly("gate add-waiter")
+
+		gateID := args[0]
+		waiter := args[1]
+		ctx := rootCtx
+
+		// Get the gate issue
+		var issue *types.Issue
+		var err error
+
+		if daemonClient != nil {
+			resp, rerr := daemonClient.Show(&rpc.ShowArgs{ID: gateID})
+			if rerr != nil {
+				fmt.Fprintf(os.Stderr, "Error: %v\n", rerr)
+				os.Exit(1)
+			}
+			if !resp.Success {
+				fmt.Fprintf(os.Stderr, "Error: %s\n", resp.Error)
+				os.Exit(1)
+			}
+			var details types.IssueDetails
+			if uerr := json.Unmarshal(resp.Data, &details); uerr != nil {
+				fmt.Fprintf(os.Stderr, "Error parsing response: %v\n", uerr)
+				os.Exit(1)
+			}
+			issue = &details.Issue
+		} else {
+			issue, err = store.GetIssue(ctx, gateID)
+			if err != nil {
+				fmt.Fprintf(os.Stderr, "Error: gate not found: %s\n", gateID)
+				os.Exit(1)
+			}
+		}
+
+		if issue.IssueType != types.TypeGate {
+			fmt.Fprintf(os.Stderr, "Error: %s is not a gate issue (type=%s)\n", gateID, issue.IssueType)
+			os.Exit(1)
+		}
+
+		// Check if waiter is already registered
+		for _, w := range issue.Waiters {
+			if w == waiter {
+				fmt.Printf("Waiter already registered on gate %s\n", gateID)
+				return
+			}
+		}
+
+		// Add waiter to the waiters list
+		newWaiters := append(issue.Waiters, waiter)
+
+		// Update the gate
+		if daemonClient != nil {
+			updateArgs := &rpc.UpdateArgs{
+				ID:      gateID,
+				Waiters: newWaiters,
+			}
+			resp, uerr := daemonClient.Update(updateArgs)
+			if uerr != nil {
+				fmt.Fprintf(os.Stderr, "Error: %v\n", uerr)
+				os.Exit(1)
+			}
+			if !resp.Success {
+				fmt.Fprintf(os.Stderr, "Error: %s\n", resp.Error)
+				os.Exit(1)
+			}
+		} else {
+			updates := map[string]interface{}{
+				"waiters": newWaiters,
+			}
+			if err := store.UpdateIssue(ctx, gateID, updates, actor); err != nil {
+				fmt.Fprintf(os.Stderr, "Error updating gate: %v\n", err)
+				os.Exit(1)
+			}
+			markDirtyAndScheduleFlush()
+		}
+
+		fmt.Printf("%s Added waiter to gate %s: %s\n", ui.RenderPass("✓"), gateID, waiter)
+	},
+}
+
+// gateShowCmd shows a gate issue
+var gateShowCmd = &cobra.Command{
+	Use:   "show <gate-id>",
+	Short: "Show a gate issue",
+	Long: `Display details of a gate issue including its waiters.
+
+This is similar to 'bd show' but validates that the issue is a gate.`,
+	Args: cobra.ExactArgs(1),
+	Run: func(cmd *cobra.Command, args []string) {
+		gateID := args[0]
+		ctx := rootCtx
+
+		// Get the gate issue
+		var issue *types.Issue
+		var err error
+
+		if daemonClient != nil {
+			resp, rerr := daemonClient.Show(&rpc.ShowArgs{ID: gateID})
+			if rerr != nil {
+				fmt.Fprintf(os.Stderr, "Error: %v\n", rerr)
+				os.Exit(1)
+			}
+			if !resp.Success {
+				fmt.Fprintf(os.Stderr, "Error: %s\n", resp.Error)
+				os.Exit(1)
+			}
+			var details types.IssueDetails
+			if uerr := json.Unmarshal(resp.Data, &details); uerr != nil {
+				fmt.Fprintf(os.Stderr, "Error parsing response: %v\n", uerr)
+				os.Exit(1)
+			}
+			issue = &details.Issue
+		} else {
+			issue, err = store.GetIssue(ctx, gateID)
+			if err != nil {
+				fmt.Fprintf(os.Stderr, "Error: gate not found: %s\n", gateID)
+				os.Exit(1)
+			}
+		}
+
+		if issue.IssueType != types.TypeGate {
+			fmt.Fprintf(os.Stderr, "Error: %s is not a gate issue (type=%s)\n", gateID, issue.IssueType)
+			os.Exit(1)
+		}
+
+		if jsonOutput {
+			outputJSON(issue)
+			return
+		}
+
+		// Display gate details
+		statusSym := "○"
+		if issue.Status == types.StatusClosed {
+			statusSym = "●"
+		}
+
+		fmt.Printf("%s %s - %s\n", statusSym, ui.RenderID(issue.ID), issue.Title)
+		fmt.Printf("  Status: %s\n", issue.Status)
+		fmt.Printf("  Await Type: %s\n", issue.AwaitType)
+		if issue.AwaitID != "" {
+			fmt.Printf("  Await ID: %s\n", issue.AwaitID)
+		}
+		if issue.Timeout > 0 {
+			fmt.Printf("  Timeout: %s\n", issue.Timeout)
+		}
+		if len(issue.Waiters) > 0 {
+			fmt.Printf("  Waiters:\n")
+			for _, w := range issue.Waiters {
+				fmt.Printf("    - %s\n", w)
+			}
+		}
+		if issue.Description != "" {
+			fmt.Printf("  Description: %s\n", issue.Description)
+		}
+	},
+}
+
 // gateResolveCmd manually closes a gate
 var gateResolveCmd = &cobra.Command{
 	Use:   "resolve <gate-id>",
@@ -703,8 +872,10 @@ func init() {
 
 	// Add subcommands
 	gateCmd.AddCommand(gateListCmd)
+	gateCmd.AddCommand(gateShowCmd)
 	gateCmd.AddCommand(gateResolveCmd)
 	gateCmd.AddCommand(gateCheckCmd)
+	gateCmd.AddCommand(gateAddWaiterCmd)
 
 	rootCmd.AddCommand(gateCmd)
 }