The fast/thin path (short acks like "10-4", enabled to attempt linking at
all by 1ffff25) had no identity signal available -- transcript_too_short
skips GPT extraction entirely, so call_units is always empty for this
population. It fell back to "most recently updated incident on this
talkgroup", which silently misattaches a short ack to the wrong incident
whenever two are live on the same busy dispatch channel at once.
metadata_watcher.py already captures the P25 source radio ID (srcaddr) on
every call independent of transcript content, and it already reaches the
call doc (models.py, mqtt_handler.py:245) -- it was just never read by the
correlator. Thread it through _build_context, check it against the
srcaddrs already seen on each TG-matched incident before falling back to
recency, and accumulate it on the incident (_update_incident/_create_incident)
so later calls from the same radio can match.
Verified: 422 pass, 0 fail (4 new tests).
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>