Re-evaluate incident severity on link, stamp resolved_at at every resolution site

#17: severity was written once at _create_incident and never touched again,
so an incident that opened routine and escalated to a working fire stayed
routine forever. _update_incident now merges call_severity into the incident
via _max_severity() on every link.

Severity is monotonic: it only ever rises, never falls. An incident briefly
assessed "major" genuinely was major at that moment; a later, calmer-sounding
call is evidence the situation is winding down, not that the earlier read was
wrong. status/resolved_at exist to retire an incident — severity should stay
as the high-water mark so the worst-first rail, "Major only" filter, and map
colouring never bury a call that was genuinely major. See _max_severity's
docstring in incident_correlator.py for the full argument.

#18: none of the resolution sites wrote resolved_at, so an incident's
lifespan couldn't be reconstructed for the history-scrub feature. Added
resolved_at alongside status="resolved" at all six sites that flip it:
  - incident_correlator.py _update_incident (signal-based: units all cleared)
  - incident_correlator.py maybe_resolve_parent (master auto-resolve)
  - summarizer.py _stale_sweep (90-minute auto-resolve)
  - upload.py, both scene-resolution loops (single- and multi-scene)
  - calls.py reprocess/correction path
(_update_incident's signal-resolve and maybe_resolve_parent's master-resolve
weren't named in the issue's four call sites, but they set status the same
way and were missing resolved_at too.)

No backfill: existing resolved incidents keep resolved_at = null, which
means "resolved before this field existed," not "never resolved." Backfilling
from updated_at would be a guess dressed up as data.

Tests: added to tests/test_correlator_gate.py, which needs no Firestore for
the pure _max_severity cases and patches fstore for the _update_incident/
maybe_resolve_parent writes. Covers the escalation case (routine -> major),
the no-downgrade case, and resolved_at on both the signal-resolve and
master-resolve paths. 52/52 passing in that file; 83 passed / 10
pre-existing failures for drb-c2-core overall (baseline was 69/10 — the
+14 is exactly the new tests, no regressions).

Fixes #17, #18.

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

@@ -51,6 +51,32 @@ _PURSUIT_TAGS = frozenset({
     "fleeing-vehicle", "suspect-vehicle", "eluding",
 })
 
+# Four-level severity ladder, low → high (see intelligence.py EXTRACTION_PROMPT).
+_SEVERITY_RANK = {"routine": 0, "minor": 1, "moderate": 2, "major": 3}
+
+
+def _max_severity(current: Optional[str], new: Optional[str]) -> str:
+    """
+    Highest of two severities on the four-level ladder — the merge rule used
+    every time a call attaches to an existing incident.
+
+    Severity is monotonic by design: it only ever rises, never falls, as more
+    calls link. An incident briefly assessed "major" genuinely was major at
+    that moment; a later call that sounds calmer ("units clear", dispatcher
+    moving on) is evidence the SITUATION is winding down, not that the earlier
+    read was wrong. That's what `status`/`resolved_at` are for — resolution
+    retires an incident, it doesn't retroactively erase how serious it was.
+    Every severity-driven surface (worst-first incident rail, "Major only"
+    filter, map colour) exists to make sure a major event is never missed;
+    downgrading severity mid-incident would silently defeat that on the exact
+    incidents it exists to protect. A malformed/unrecognized value from either
+    side ranks as "routine" so it can never suppress a real escalation.
+    """
+    current = current if current in _SEVERITY_RANK else "routine"
+    new     = new if new in _SEVERITY_RANK else "routine"
+    return current if _SEVERITY_RANK[current] >= _SEVERITY_RANK[new] else new
+
+
 # Maximum plausible ground speed for a moving incident (pursuit/transport).
 # ~3 miles/min ≈ 180 mph — well above real pursuit speeds, but generous enough
 # to tolerate GPS drift and call-timing jitter.  Anything faster is a bad geocode
@@ -877,6 +903,7 @@ async def _apply_decision(decision: dict, ctx: dict) -> Optional[str]:
             location, location_coords, call_units, call_vehicles, call_embedding, now,
             talkgroup_name=talkgroup_name, incident_type=incident_type,
             cleared_units=call_cleared, refresh_activity=not thin_link,
+            call_severity=call_severity,
         )
         return matched_incident["incident_id"]
 
@@ -1251,6 +1278,7 @@ async def _update_incident(
     incident_type: Optional[str] = None,
     cleared_units: Optional[list[str]] = None,
     refresh_activity: bool = True,
+    call_severity: Optional[str] = None,
 ) -> None:
     incident_id = inc["incident_id"]
 
@@ -1303,6 +1331,7 @@ async def _update_incident(
         "units_cleared":     units_cleared,
         "location_mentions": location_mentions,
         "summary_stale":     True,
+        "severity":          _max_severity(inc.get("severity"), call_severity),
         **embedding_updates,
     }
 
@@ -1347,6 +1376,7 @@ async def _update_incident(
     # don't fire on incidents where units were never tracked (no unit mentions at all).
     if units_cleared and not units_active:
         updates["status"] = "resolved"
+        updates["resolved_at"] = now.isoformat()
         await fstore.doc_set("incidents", incident_id, updates)
         logger.info(
             f"Correlator: signal-resolved incident {incident_id} "
@@ -1538,7 +1568,10 @@ async def maybe_resolve_parent(incident_id: str) -> None:
             return  # at least one sibling still active
 
     # All children resolved — close the master
-    await fstore.doc_set("incidents", parent_id, {"status": "resolved"})
+    await fstore.doc_set("incidents", parent_id, {
+        "status": "resolved",
+        "resolved_at": datetime.now(timezone.utc).isoformat(),
+    })
     logger.info(
         f"Auto-resolved master incident {parent_id} "
         f"(all {len(child_ids)} child(ren) resolved)"

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

@@ -101,7 +101,10 @@ async def _resolve_stale_incidents() -> None:
                 updated_dt = updated_dt.replace(tzinfo=timezone.utc)
             idle_minutes = (now - updated_dt).total_seconds() / 60
             if idle_minutes > settings.incident_auto_resolve_minutes:
-                await fstore.doc_set("incidents", incident_id, {"status": "resolved"})
+                await fstore.doc_set("incidents", incident_id, {
+                    "status": "resolved",
+                    "resolved_at": now.isoformat(),
+                })
                 from app.internal.incident_correlator import maybe_resolve_parent
                 await maybe_resolve_parent(incident_id)
                 logger.info(

drb-c2-core/app/routers/calls.py

@@ -173,6 +173,7 @@ async def patch_transcript(
                 await fstore.doc_set("incidents", old_incident_id, {
                     "call_ids": [],
                     "status": "resolved",
+                    "resolved_at": datetime.now(timezone.utc).isoformat(),
                     "summary_stale": True,
                 })
     await fstore.doc_set("calls", call_id, {"incident_ids": [], "incident_id": None})

drb-c2-core/app/routers/upload.py

@@ -1,4 +1,5 @@
 from typing import Optional
+from datetime import datetime, timezone
 from fastapi import APIRouter, BackgroundTasks, UploadFile, File, Form, HTTPException, Security
 from fastapi.security import HTTPBearer, HTTPAuthorizationCredentials
 from app.internal.storage import upload_audio
@@ -202,7 +203,10 @@ async def _run_extraction_pipeline(
         if incident_id and incident_id not in incident_ids:
             incident_ids.append(incident_id)
         if scene["resolved"] and incident_id:
-            await fstore.doc_set("incidents", incident_id, {"status": "resolved"})
+            await fstore.doc_set("incidents", incident_id, {
+                "status": "resolved",
+                "resolved_at": datetime.now(timezone.utc).isoformat(),
+            })
             await incident_correlator.maybe_resolve_parent(incident_id)
             logger.info(f"Auto-resolved incident {incident_id} (LLM closure detection)")
 
@@ -305,7 +309,10 @@ async def _run_intelligence_pipeline(
             if incident_id and incident_id not in incident_ids:
                 incident_ids.append(incident_id)
             if scene["resolved"] and incident_id:
-                await fstore.doc_set("incidents", incident_id, {"status": "resolved"})
+                await fstore.doc_set("incidents", incident_id, {
+                    "status": "resolved",
+                    "resolved_at": datetime.now(timezone.utc).isoformat(),
+                })
                 await incident_correlator.maybe_resolve_parent(incident_id)
                 logger.info(f"Auto-resolved incident {incident_id} (LLM closure detection)")
 

drb-c2-core/tests/test_correlator_gate.py

@@ -18,6 +18,7 @@ from datetime import datetime, timedelta, timezone
 from unittest.mock import AsyncMock, patch
 from app.internal.incident_correlator import (
     _run_decision, _update_incident, _normalize_unit, _matching_units,
+    _max_severity, maybe_resolve_parent,
 )
 
 NOW = datetime(2026, 8, 16, 21, 0, 0, tzinfo=timezone.utc)
@@ -247,3 +248,117 @@ def test_normalised_units_link_a_call_that_exact_match_would_orphan():
         call_units=["K-9A2"], is_thin_call=False, call_severity="routine",
     ))
     assert decision["action"] == "link"
+
+
+# ---------------------------------------------------------------------------
+# Issue #17 — severity re-evaluation as calls attach (monotonic ladder)
+#
+# Decision: severity only ever rises, never falls, as more calls link (see
+# _max_severity's docstring in incident_correlator.py for the full argument).
+# An incident briefly assessed "major" genuinely was major at that moment;
+# resolution (status/resolved_at), not a later calmer-sounding call, is what
+# retires it. These tests lock in both halves of that: escalation raises the
+# stored severity, and a later lower-severity call does not undo it.
+# ---------------------------------------------------------------------------
+
+@pytest.mark.parametrize("current,new,expected", [
+    ("routine",  "major",    "major"),      # escalation — the motivating case
+    ("routine",  "minor",    "minor"),
+    ("minor",    "moderate", "moderate"),
+    ("major",    "routine",  "major"),      # calmer call does NOT downgrade
+    ("major",    "minor",    "major"),
+    ("moderate", "moderate", "moderate"),   # tie
+    (None,       "moderate", "moderate"),   # incident with no prior severity
+    ("major",    None,       "major"),
+    ("major",    "bogus",    "major"),      # malformed value ranks as routine
+    ("bogus",    "minor",    "minor"),
+])
+def test_max_severity_is_monotonic(current, new, expected):
+    assert _max_severity(current, new) == expected
+
+
+@pytest.mark.asyncio
+async def test_escalating_call_raises_stored_incident_severity():
+    """The #17 motivating case: an incident opened routine, a later call is a
+    working structure fire — the incident's severity must reflect it."""
+    inc = _incident(2.0)
+    inc["severity"] = "routine"
+    with patch("app.internal.incident_correlator.fstore") as mock_fstore:
+        mock_fstore.doc_set = AsyncMock()
+        await _update_incident(
+            inc, "call-2", 9048, "sys-1", [], None, None, [], [], None, NOW,
+            call_severity="major",
+        )
+    updates = mock_fstore.doc_set.await_args.args[2]
+    assert updates["severity"] == "major"
+
+
+@pytest.mark.asyncio
+async def test_calmer_followup_call_does_not_downgrade_severity():
+    inc = _incident(2.0)
+    inc["severity"] = "major"
+    with patch("app.internal.incident_correlator.fstore") as mock_fstore:
+        mock_fstore.doc_set = AsyncMock()
+        await _update_incident(
+            inc, "call-2", 9048, "sys-1", [], None, None, [], [], None, NOW,
+            call_severity="routine",
+        )
+    updates = mock_fstore.doc_set.await_args.args[2]
+    assert updates["severity"] == "major"
+
+
+# ---------------------------------------------------------------------------
+# Issue #18 — every resolution site stamps resolved_at
+#
+# updated_at is not a substitute (thin/ack calls deliberately don't move it,
+# unrelated field updates do) and existing rows are left null, not backfilled
+# — null means "resolved before this field existed", not "never resolved".
+# ---------------------------------------------------------------------------
+
+@pytest.mark.asyncio
+async def test_signal_resolve_stamps_resolved_at():
+    """All tracked units clear -> _update_incident's own auto-resolve path."""
+    inc = _incident(2.0)
+    inc["units_active"] = ["6-Adam"]
+    with patch("app.internal.incident_correlator.fstore") as mock_fstore:
+        mock_fstore.doc_set = AsyncMock()
+        # standalone incident — maybe_resolve_parent's own doc_get short-circuits on None
+        mock_fstore.doc_get = AsyncMock(return_value=None)
+        await _update_incident(
+            inc, "call-2", 9048, "sys-1", [], None, None, [], [], None, NOW,
+            cleared_units=["6-Adam"],
+        )
+    updates = mock_fstore.doc_set.await_args.args[2]
+    assert updates["status"] == "resolved"
+    assert updates["resolved_at"] == NOW.isoformat()
+
+
+@pytest.mark.asyncio
+async def test_master_auto_resolve_stamps_resolved_at():
+    """maybe_resolve_parent closes a master once every child has resolved."""
+    child_a = {"incident_id": "child-a", "parent_incident_id": "master-1"}
+    master  = {
+        "incident_id": "master-1",
+        "status": "active",
+        "child_incident_ids": ["child-a", "child-b"],
+    }
+    child_b_resolved = {"incident_id": "child-b", "status": "resolved"}
+
+    async def fake_doc_get(collection, doc_id):
+        return {
+            "child-a": child_a,
+            "master-1": master,
+            "child-b": child_b_resolved,
+        }.get(doc_id)
+
+    with patch("app.internal.incident_correlator.fstore") as mock_fstore:
+        mock_fstore.doc_get = AsyncMock(side_effect=fake_doc_get)
+        mock_fstore.doc_set = AsyncMock()
+        await maybe_resolve_parent("child-a")
+
+    mock_fstore.doc_set.assert_awaited_once()
+    args = mock_fstore.doc_set.await_args.args
+    assert args[0] == "incidents"
+    assert args[1] == "master-1"
+    assert args[2]["status"] == "resolved"
+    assert "resolved_at" in args[2] and args[2]["resolved_at"]