correlator: address drb-correlation-review notes on #139

- Document call_severity's routine-coercion asymmetry with incident_type
  (extraction-said-routine vs extraction-said-nothing look identical).
- Test docstring no longer overclaims the ctx-linkage it doesn't cover;
  points to the tests that do (test_consensus_gate.py, test_incident_identity.py).
- scene1 now uses a distinct severity so the test actually exercises both
  fields symmetrically; the 'no flat top-level clobber' claim is now
  asserted, not just commented.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Tbknwttzou4s46PAykmtix

drb-c2-core/tests/test_per_scene_call_doc.py

@@ -135,9 +135,12 @@ async def test_scene_entry_captures_its_own_incident_type_not_a_sibling_scenes()
     server-26#139: _call_is_substanceless's "type" veto reads ctx["incident_type"]
     at decision time, but that value was never persisted per-scene — only the
     last-scene-wins flat field, which #138's dump analysis couldn't
-    distinguish from cross-scene contamination. Each scene's own scenes.<n>
-    entry must carry its own incident_type/severity, distinct from any other
-    scene on the same call.
+    distinguish from cross-scene contamination. Pins _apply_and_log's write
+    side: each scene's own scenes.<n> entry carries its own incident_type/
+    severity, distinct from any other scene on the same call. Does NOT cover
+    whether the ctx handed to _call_is_substanceless is the same object that
+    reaches here — that linkage is pinned by test_consensus_gate.py and
+    test_incident_identity.py, not this file.
     """
     docs: dict[tuple, dict] = {}
 
@@ -160,7 +163,7 @@ async def test_scene_entry_captures_its_own_incident_type_not_a_sibling_scenes()
     }
     ctx1 = {
         "call_id": "call-5", "scene_index": 1, "scene_transcript": "roll call",
-        "incident_type": None, "call_severity": "routine",
+        "incident_type": None, "call_severity": "moderate",
     }
 
     with patch.object(incident_correlator, "fstore") as mock_fstore:
@@ -168,13 +171,16 @@ async def test_scene_entry_captures_its_own_incident_type_not_a_sibling_scenes()
         await incident_correlator._apply_and_log(decision0, ctx0)
         await incident_correlator._apply_and_log(decision1, ctx1)
 
-    scenes = docs[("calls", "call-5")]["scenes"]
+    doc = docs[("calls", "call-5")]
+    scenes = doc["scenes"]
     assert scenes["0"]["incident_type"] == "traffic-stop"
     assert scenes["0"]["severity"] == "routine"
     assert scenes["1"]["incident_type"] is None
-    # _apply_and_log never writes incident_type/severity to the flat
-    # top-level fields at all (only corr_debug's own keys go flat) — the
-    # per-scene entry is the only place either value is ever persisted.
+    assert scenes["1"]["severity"] == "moderate"
+    # _apply_and_log only ever flat-merges corr_debug's own keys (:1460) — a
+    # future corr_debug["incident_type"] would silently clobber
+    # intelligence.py's flat field, so this is asserted, not just commented.
+    assert "incident_type" not in doc
 
 
 @pytest.mark.asyncio