Follow-up to the salvaged #71867 supervision fix. _spawn_supervised's own
backoff respawn created a new task without updating the external handle
self._reconnect_watcher_task, so after the reconnect watcher crashed and
self-restarted, _ensure_reconnect_watcher_running() saw the stale handle as
done() and spawned a SECOND concurrent watcher (double reconnect attempts).
Add an optional on_spawn callback to _spawn_supervised, fired with the live
task on every spawn INCLUDING internal respawns, and pass it at both reconnect-
watcher spawn sites so the tracked handle always advances. The two supervision
mechanisms (supervisor auto-restart + ensure-respawn) now compose instead of
racing. Regression test sabotage-verified.
teknium1
bd7938fa0c