gt handoff was calling KillPaneProcesses which killed Claude Code
(the pane process) before RespawnPane could be called. This caused
handoff to silently fail with no respawn.
Add KillPaneProcessesExcluding function that allows excluding specific
PIDs from being killed. The self-handoff path now excludes the current
process and its parent (Claude Code) so gt handoff survives long enough
to call RespawnPane. The -k flag on respawn-pane handles final cleanup.
Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>