fix(handoff): prevent race condition when killing pane processes

KillPaneProcesses was killing ALL processes in the pane, including the
gt handoff process itself. This created a race condition where the
process could be killed before RespawnPane executes, causing the pane
to close prematurely and requiring manual reattach.

Added KillPaneProcessesExcluding() function that excludes specified PIDs
from being killed. The handoff command now passes its own PID to avoid
the race condition.

Fixes: gt-85qd

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

internal/cmd/handoff.go

@@ -206,7 +206,10 @@ func runHandoff(cmd *cobra.Command, args []string) error {
 
 	// Kill all processes in the pane before respawning to prevent orphan leaks
 	// RespawnPane's -k flag only sends SIGHUP which Claude/Node may ignore
-	if err := t.KillPaneProcesses(pane); err != nil {
+	// IMPORTANT: Exclude our own process to avoid race condition where we get killed
+	// before RespawnPane executes, causing the pane to close prematurely (gt-85qd)
+	myPID := fmt.Sprintf("%d", os.Getpid())
+	if err := t.KillPaneProcessesExcluding(pane, []string{myPID}); err != nil {
 		// Non-fatal but log the warning
 		style.PrintWarning("could not kill pane processes: %v", err)
 	}