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.
Land the `decnet bus` worker and `get_bus()` factory. Transport is a
host-local UNIX-domain socket (0660, group=decnet); authz is the file
mode. Wire framing is a tiny verb-line + 4-byte-BE length + orjson body.
NATS-style wildcard topics (`*`, `>`). At-most-once, fire-and-forget —
DB stays the source of truth. `FakeBus` / `NullBus` for tests and the
disabled path. Cross-host federation is deferred to a future
`--bridge-tcp` mode; DEBT-030 is master-only and unblocked.
