The orphan reaper for stdio MCP subprocesses only tracked the direct child
PID spawned by ``stdio_client`` (e.g. ``openclaw mcp serve``). When that
wrapper itself spawned a helper (``claude mcp serve``) and then exited, the
helper reparented to ``systemd --user`` and survived shutdown.
The MCP SDK already spawns stdio children with ``start_new_session=True``,
so the wrapper is its own pgroup leader and same-pgroup descendants are
reachable via ``killpg``. Capture the pgid at spawn time and reap via
``killpg(pgid, sig)`` so reparented grandchildren are reaped alongside the
direct child, even after the wrapper itself exits. Falls back to per-pid
``os.kill`` on Windows or when no pgid was recorded.
Fixes part 2 (orphan ``claude mcp serve``) of #23799. Part 1 (per-invocation
respawn) was confirmed by the reporter to be an environmental artifact, not
a code bug.
a29d64e50c