correlator: judge each scene on its own embedding + severity (server-26#80, #95)

intelligence.py writes only the primary scene's embedding and severity to
calls/{id}. _build_context read them back off the call doc, so every
non-primary scene of a multi-scene call was correlated against scene 1's
semantic vector and severity rung: a scene about a different event scored
on the embedding path against the wrong incident, and could inherit a
minor/moderate/major severity it never had, clearing the creation gate on
borrowed weight. Same defect and same fix as the #87 coords leak.

- _build_context / preview_correlation / correlate_call: take embedding and
  severity as params; drop the call_doc.get() fallbacks. A scene that
  passes none has none, and is judged thin on its own signal.
- upload.py: both scene loops pass scene["embedding"] / scene["severity"];
  _correlate_with_consensus forwards them. The no-scene unclassified branch
  passes neither (correct: no scene, judged thin).
- recorrelation_sweep: passes the call doc's stored values explicitly
  (whole-call re-link, link-only, so a borrowed severity cannot create).
- intelligence.py: SCENE DETECTION prompt tightened toward one scene
  (server-26#5, partial) - MULTIPLE only for genuinely separate events,
  "when unsure, one scene", plus a not-a-new-scene list.
- test_incident_identity.py: +2 regression tests mirroring the #87 test.

Full c2-core suite green (295 passed). #5 prompt change is unmeasured -
needs a scoped correlation-only window. Known remaining legs, tracked
separately: llm_correlator._call_block still reads the whole-call
transcript per scene; content-divergence veto skips on a None embedding.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

drb-c2-core/app/internal/recorrelation_sweep.py

@@ -90,6 +90,11 @@ async def _recorrelate_orphan(call: dict) -> bool:
         return False
 
     # All data needed for correlation was stored by the first-pass extraction.
+    # embedding/severity are no longer read from the call doc inside
+    # _build_context (server-26#80/#95) — the sweep re-links a whole call, not a
+    # scene, so it passes the call doc's stored (primary-scene) values here. It
+    # is link-only (create_if_new=False), so a borrowed severity cannot open a
+    # new incident off this path.
     incident_id = await incident_correlator.correlate_call(
         call_id        = call_id,
         node_id        = call.get("node_id", ""),
@@ -101,6 +106,8 @@ async def _recorrelate_orphan(call: dict) -> bool:
         location       = call.get("location"),
         location_coords= call.get("location_coords"),
         cleared_units  = call.get("cleared_units") or [],
+        embedding      = call.get("embedding"),
+        severity       = call.get("severity"),
         reference_time = started_at,   # anchor window to when the call happened
         create_if_new  = False,        # never create — link-only
     )