correlator: use srcaddr for thin-call disambiguation instead of pure recency (#158)

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>

drb-c2-core/tests/test_correlator_merge_caps.py

@@ -180,6 +180,55 @@ def test_tactical_thin_call_is_ambiguous_with_two_candidates():
     assert decision["action"] == "orphan"
 
 
+# ---------------------------------------------------------------------------
+# server-26#158: srcaddr identity beats recency guesswork for thin calls
+# ---------------------------------------------------------------------------
+
+def test_thin_call_srcaddr_match_resolves_tier2_ambiguity():
+    """
+    Same fixture as test_tactical_thin_call_is_ambiguous_with_two_candidates —
+    two candidates, tier-2 window, no unit ID parsed (transcript_too_short
+    skipped GPT). Without srcaddr this orphans. With it, the radio that sent
+    the call already touched inc-b, so that's the thread — not a guess.
+    """
+    a = _incident(idle_minutes=3.0, incident_id="inc-a", srcaddrs=["9001"])
+    b = _incident(idle_minutes=4.0, incident_id="inc-b", srcaddrs=["9002"])
+    decision = _run_decision(_ctx(
+        all_active=[a, b], recent=[a, b], talkgroup_name=TACTICAL_TG,
+        call_srcaddr="9002",
+    ))
+    assert decision["action"] == "link"
+    assert decision["matched_incident"]["incident_id"] == "inc-b"
+    assert decision["corr_debug"]["corr_fit_signal"] == "thin_srcaddr_match"
+
+
+def test_thin_call_srcaddr_match_overrides_recency_in_tier1():
+    """
+    Both candidates are inside the 30s conversational window, where recency
+    alone would pick inc-a (more recently updated) even though the radio that
+    sent this call has only ever touched inc-b — the exact busy-channel,
+    two-concurrent-incidents misattach server-26#158 was filed for.
+    """
+    a = _incident(idle_minutes=0.1, incident_id="inc-a", srcaddrs=["9001"])
+    b = _incident(idle_minutes=0.2, incident_id="inc-b", srcaddrs=["9002"])
+    decision = _run_decision(_ctx(
+        all_active=[a, b], recent=[a, b], call_srcaddr="9002",
+    ))
+    assert decision["action"] == "link"
+    assert decision["matched_incident"]["incident_id"] == "inc-b"
+
+
+def test_thin_call_with_no_srcaddr_match_falls_back_to_recency():
+    """A radio ID that matches nothing on this talkgroup behaves exactly as
+    before — no regression for the ordinary case."""
+    a = _incident(idle_minutes=0.1, incident_id="inc-a", srcaddrs=["9001"])
+    decision = _run_decision(_ctx(
+        all_active=[a], recent=[a], call_srcaddr="unrelated-radio",
+    ))
+    assert decision["action"] == "link"
+    assert decision["corr_debug"]["corr_fit_signal"] == "thin_recency"
+
+
 def test_call_with_unit_overlap_does_attach():
     """
     Positive control: real evidence still links. Carrying units also means the