feat: add gt stop --all emergency shutdown command

- gt stop --all: Kill all sessions across all rigs
- gt stop --rig <name>: Kill sessions in specific rig
- gt stop --graceful: Try graceful shutdown before force kill
- Captures session output before stopping
- Reports success/failure summary

Closes gt-u1j.22

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

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

internal/cmd/stop.go

@@ -0,0 +1,178 @@
+package cmd
+
+import (
+	"fmt"
+	"path/filepath"
+
+	"github.com/spf13/cobra"
+	"github.com/steveyegge/gastown/internal/config"
+	"github.com/steveyegge/gastown/internal/git"
+	"github.com/steveyegge/gastown/internal/rig"
+	"github.com/steveyegge/gastown/internal/session"
+	"github.com/steveyegge/gastown/internal/style"
+	"github.com/steveyegge/gastown/internal/tmux"
+	"github.com/steveyegge/gastown/internal/workspace"
+)
+
+var (
+	stopAll      bool
+	stopRig      string
+	stopGraceful bool
+)
+
+var stopCmd = &cobra.Command{
+	Use:   "stop",
+	Short: "Emergency stop for sessions",
+	Long: `Emergency stop command for Gas Town sessions.
+
+Stops all running polecat sessions across rigs. Use for emergency shutdown
+when you need to halt all agent activity immediately.
+
+Examples:
+  gt stop --all              # Kill ALL sessions across all rigs
+  gt stop --rig wyvern       # Kill all sessions in the wyvern rig
+  gt stop --all --graceful   # Try graceful shutdown first`,
+	RunE: runStop,
+}
+
+func init() {
+	stopCmd.Flags().BoolVar(&stopAll, "all", false, "Stop all sessions across all rigs")
+	stopCmd.Flags().StringVar(&stopRig, "rig", "", "Stop all sessions in a specific rig")
+	stopCmd.Flags().BoolVar(&stopGraceful, "graceful", false, "Try graceful shutdown before force kill")
+	rootCmd.AddCommand(stopCmd)
+}
+
+// StopResult tracks what was stopped.
+type StopResult struct {
+	Rig       string
+	Polecat   string
+	SessionID string
+	Success   bool
+	Error     string
+}
+
+func runStop(cmd *cobra.Command, args []string) error {
+	if !stopAll && stopRig == "" {
+		return fmt.Errorf("must specify --all or --rig <name>")
+	}
+
+	// Find town root
+	townRoot, err := workspace.FindFromCwdOrError()
+	if err != nil {
+		return fmt.Errorf("not in a Gas Town workspace: %w", err)
+	}
+
+	// Load rigs config
+	rigsConfigPath := filepath.Join(townRoot, "config", "rigs.json")
+	rigsConfig, err := config.LoadRigsConfig(rigsConfigPath)
+	if err != nil {
+		rigsConfig = &config.RigsConfig{Rigs: make(map[string]config.RigEntry)}
+	}
+
+	// Get rigs to stop
+	g := git.NewGit(townRoot)
+	rigMgr := rig.NewManager(townRoot, rigsConfig, g)
+	rigs, err := rigMgr.DiscoverRigs()
+	if err != nil {
+		return fmt.Errorf("discovering rigs: %w", err)
+	}
+
+	// Filter by rig if specified
+	if stopRig != "" {
+		var filtered []*rig.Rig
+		for _, r := range rigs {
+			if r.Name == stopRig {
+				filtered = append(filtered, r)
+			}
+		}
+		if len(filtered) == 0 {
+			return fmt.Errorf("rig '%s' not found", stopRig)
+		}
+		rigs = filtered
+	}
+
+	// Determine force mode
+	force := !stopGraceful
+
+	if stopAll {
+		fmt.Printf("%s Stopping ALL Gas Town sessions...\n\n",
+			style.Bold.Render("🛑"))
+	} else {
+		fmt.Printf("%s Stopping sessions in rig '%s'...\n\n",
+			style.Bold.Render("🛑"), stopRig)
+	}
+
+	// Stop sessions in each rig
+	t := tmux.NewTmux()
+	var results []StopResult
+	stopped := 0
+
+	for _, r := range rigs {
+		mgr := session.NewManager(t, r)
+		infos, err := mgr.List()
+		if err != nil {
+			continue
+		}
+
+		for _, info := range infos {
+			result := StopResult{
+				Rig:       r.Name,
+				Polecat:   info.Polecat,
+				SessionID: info.SessionID,
+			}
+
+			// Capture output before stopping (best effort)
+			output, _ := mgr.Capture(info.Polecat, 50)
+
+			// Stop the session
+			err := mgr.Stop(info.Polecat, force)
+			if err != nil {
+				result.Success = false
+				result.Error = err.Error()
+				fmt.Printf("  %s [%s] %s: %s\n",
+					style.Dim.Render("✗"),
+					r.Name, info.Polecat,
+					style.Dim.Render(err.Error()))
+			} else {
+				result.Success = true
+				stopped++
+				fmt.Printf("  %s [%s] %s: stopped\n",
+					style.Bold.Render("✓"),
+					r.Name, info.Polecat)
+
+				// Log captured output (truncated)
+				if len(output) > 200 {
+					output = output[len(output)-200:]
+				}
+				if output != "" {
+					fmt.Printf("      %s\n", style.Dim.Render("(output captured)"))
+				}
+			}
+
+			results = append(results, result)
+		}
+	}
+
+	// Summary
+	fmt.Println()
+	if stopped == 0 {
+		fmt.Println("No active sessions to stop.")
+	} else {
+		fmt.Printf("%s %d session(s) stopped.\n",
+			style.Bold.Render("✓"), stopped)
+	}
+
+	// Report failures
+	failures := 0
+	for _, r := range results {
+		if !r.Success {
+			failures++
+		}
+	}
+	if failures > 0 {
+		fmt.Printf("%s %d session(s) failed to stop.\n",
+			style.Dim.Render("⚠"), failures)
+	}
+
+	return nil
+}