Smart attach: link window when inside tmux

When 'gt X attach' is run from inside a tmux session, link the target
session's window as a new tab instead of switching sessions entirely.
Use C-b n/p to navigate between tabs.

Outside tmux: unchanged behavior (full attach)
Inside tmux: links window as tab for convenient multi-session viewing

- Add tmux.LinkWindow() and tmux.IsInsideTmux()
- Update attachToTmuxSession() with smart detection
- Update mayor, deacon, crew, refinery attach commands

internal/cmd/crew_helpers.go

@@ -12,6 +12,7 @@ import (
 	"github.com/steveyegge/gastown/internal/git"
 	"github.com/steveyegge/gastown/internal/rig"
 	"github.com/steveyegge/gastown/internal/style"
+	"github.com/steveyegge/gastown/internal/tmux"
 	"github.com/steveyegge/gastown/internal/workspace"
 )
 
@@ -168,8 +169,21 @@ func isInTmuxSession(targetSession string) bool {
 	return currentSession == targetSession
 }
 
-// attachToTmuxSession attaches to a tmux session with proper TTY forwarding.
+// attachToTmuxSession attaches to a tmux session with smart behavior:
+// - If already inside tmux: links the session as a new tab (use C-b n/p to switch)
+// - If outside tmux: attaches normally (takes over terminal)
 func attachToTmuxSession(sessionID string) error {
+	// If already inside tmux, link the window as a tab instead of switching sessions
+	if tmux.IsInsideTmux() {
+		t := tmux.NewTmux()
+		if err := t.LinkWindow(sessionID, 0); err != nil {
+			return fmt.Errorf("linking window: %w", err)
+		}
+		fmt.Printf("Linked %s as a new tab. Use C-b n to switch to it.\n", sessionID)
+		return nil
+	}
+
+	// Outside tmux: attach normally
 	tmuxPath, err := exec.LookPath("tmux")
 	if err != nil {
 		return fmt.Errorf("tmux not found: %w", err)

internal/cmd/deacon.go

@@ -3,7 +3,6 @@ package cmd
 import (
 	"errors"
 	"fmt"
-	"os/exec"
 	"strings"
 	"time"
 
@@ -199,13 +198,8 @@ func runDeaconAttach(cmd *cobra.Command, args []string) error {
 	}
 	// Session uses a respawn loop, so Claude restarts automatically if it exits
 
-	// Use exec to replace current process with tmux attach
-	tmuxPath, err := exec.LookPath("tmux")
-	if err != nil {
-		return fmt.Errorf("tmux not found: %w", err)
-	}
-
-	return execCommand(tmuxPath, "attach-session", "-t", DeaconSessionName)
+	// Use shared attach helper (smart: links if inside tmux, attaches if outside)
+	return attachToTmuxSession(DeaconSessionName)
 }
 
 func runDeaconStatus(cmd *cobra.Command, args []string) error {

internal/cmd/mayor.go

@@ -3,8 +3,6 @@ package cmd
 import (
 	"errors"
 	"fmt"
-	"os"
-	"os/exec"
 	"time"
 
 	"github.com/spf13/cobra"
@@ -179,25 +177,8 @@ func runMayorAttach(cmd *cobra.Command, args []string) error {
 		}
 	}
 
-	// Use exec to replace current process with tmux attach
-	tmuxPath, err := exec.LookPath("tmux")
-	if err != nil {
-		return fmt.Errorf("tmux not found: %w", err)
-	}
-
-	return execCommand(tmuxPath, "attach-session", "-t", MayorSessionName)
-}
-
-// execCommand replaces the current process with the given command.
-// This is used for attaching to tmux sessions.
-func execCommand(name string, args ...string) error {
-	// On Unix, we would use syscall.Exec to replace the process
-	// For portability, we use exec.Command and wait
-	cmd := exec.Command(name, args...)
-	cmd.Stdin = os.Stdin
-	cmd.Stdout = os.Stdout
-	cmd.Stderr = os.Stderr
-	return cmd.Run()
+	// Use shared attach helper (smart: links if inside tmux, attaches if outside)
+	return attachToTmuxSession(MayorSessionName)
 }
 
 func runMayorStatus(cmd *cobra.Command, args []string) error {