Worker bus instances (collector, ingester) close their private buses
in finally blocks on shutdown, but stream threads holding closure
references kept calling publish after close — one `RuntimeError:
publish on closed bus` per stream line, caught by publish_safely
and logged per call, flooding server logs.
Changes:
- `UnixSocketBus.publish()` now drops post-close calls. First drop
WARNs loudly (bus is critical infra — silent drops would hide real
problems); subsequent drops on the same instance log at DEBUG to
prevent the flood. Sticky `_closed_publish_warned` flag, reset
naturally per new bus instance.
- `make_thread_safe_publisher` short-circuits on a closed bus before
marshalling a coroutine onto the loop. Avoids the wasted scheduling
work in the hot shutdown path.
Degradation is safe: callers go through `publish_safely`, which
already treats exceptions as 'dropped notification, DB is source of
truth.' We just stop manufacturing the exception in the first place
for a known-benign condition.