diff --git a/src/central/cloudevents_wire.py b/src/central/cloudevents_wire.py
index f8e5630..1d9d776 100644
--- a/src/central/cloudevents_wire.py
+++ b/src/central/cloudevents_wire.py
@@ -22,8 +22,17 @@ def wrap_event(
                 or None to use defaults.
 
     Returns:
-        A tuple of (envelope_dict, msg_id) where msg_id is the
-        CloudEvent id for use as Nats-Msg-Id header.
+        A tuple of (envelope_dict, msg_id). ``msg_id`` is what we hand to
+        JetStream as the ``Nats-Msg-Id`` header. As of v0.10.8 it has the
+        category-discriminated shape ``"{event.id}:{event.category}"`` so
+        that an incident envelope and a perimeter envelope sharing the
+        same source GUID (e.g. wfigs_incidents and wfigs_perimeters both
+        emitting a Summit Creek IRWIN within JetStream's 2-min dedup
+        window on CENTRAL_FIRE) do NOT collide -- the subject is not part
+        of the dedup key, so the category suffix is what makes them
+        distinct. ``envelope["id"]`` itself stays the bare ``event.id``
+        per the CloudEvents spec, so subscribers that key off the
+        payload id are unaffected.
     """
     # Resolve CloudEventsConfig from various input types
     if config is None:
@@ -67,4 +76,4 @@ def wrap_event(
     envelope: dict[str, Any] = dict(ce.get_attributes())
     envelope["data"] = ce.data
 
-    return envelope, event.id
+    return envelope, f"{event.id}:{event.category}"
diff --git a/tests/test_models.py b/tests/test_models.py
index 7ed5c54..ff09e21 100644
--- a/tests/test_models.py
+++ b/tests/test_models.py
@@ -64,11 +64,17 @@ class TestCloudEventsWire:
     def test_required_fields_present(
         self, sample_event: Event, sample_config: Config
     ) -> None:
-        """Required CloudEvents fields are present."""
+        """Required CloudEvents fields are present.
+
+        v0.10.8: msg_id is now category-discriminated. The CloudEvents
+        envelope ``id`` stays the bare ``event.id`` per CE spec; only the
+        ``Nats-Msg-Id`` header (= the second return value of wrap_event)
+        carries the ``"{event.id}:{event.category}"`` shape.
+        """
         envelope, msg_id = wrap_event(sample_event, sample_config)
 
-        assert msg_id == sample_event.id
-        assert envelope["id"] == sample_event.id
+        assert msg_id == f"{sample_event.id}:{sample_event.category}"
+        assert envelope["id"] == sample_event.id  # CE spec: bare event.id
         assert envelope["source"] == sample_config.cloudevents.source
         assert envelope["type"] == "central.wx.alert.severe_thunderstorm_warning.v1"
         assert envelope["specversion"] == "1.0"
@@ -76,6 +82,77 @@ class TestCloudEventsWire:
         assert envelope["datacontenttype"] == "application/json"
         assert "data" in envelope
 
+    def test_msgid_disambiguates_incident_vs_perimeter_same_guid(
+        self, sample_geo: Geo, sample_config: Config
+    ) -> None:
+        """v0.10.8 regression guard: Summit Creek dedup collision.
+
+        On 2026-06-07 a wfigs poll yielded both an incident envelope and
+        a perimeter envelope for the same IRWIN ``{6B1C6EB1-...}`` within
+        JetStream's 2-min dedup window on CENTRAL_FIRE. Both publishes
+        carried the bare IRWIN as ``Nats-Msg-Id`` (JetStream's dedup key
+        is per-stream, NOT per-subject), so the second publish was
+        silently dropped -- supervisor logs showed 'Published event' for
+        both but only one landed in the stream. The fix adds an
+        ``:{event.category}`` suffix to the msg_id so the two are
+        distinct without changing ``envelope["id"]`` (CE spec) or the
+        adapter-side event.id contract.
+        """
+        irwin = "{6B1C6EB1-30F7-4613-9C58-4801DC8FD822}"  # Summit Creek
+        incident = Event(
+            id=irwin,
+            adapter="wfigs_incidents",
+            category="fire.incident.wildfire",
+            time=datetime(2026, 6, 7, 6, 25, 5, tzinfo=timezone.utc),
+            severity=2,
+            geo=sample_geo,
+            data={},
+        )
+        perimeter = Event(
+            id=irwin,
+            adapter="wfigs_perimeters",
+            category="fire.perimeter.wildfire",
+            time=datetime(2026, 6, 7, 6, 25, 5, tzinfo=timezone.utc),
+            severity=2,
+            geo=sample_geo,
+            data={},
+        )
+
+        _, incident_msgid = wrap_event(incident, sample_config)
+        _, perimeter_msgid = wrap_event(perimeter, sample_config)
+
+        assert incident_msgid != perimeter_msgid
+        assert incident_msgid == f"{irwin}:fire.incident.wildfire"
+        assert perimeter_msgid == f"{irwin}:fire.perimeter.wildfire"
+
+    @pytest.mark.parametrize("category", [
+        "fire.incident.wildfire",
+        "fire.perimeter.wildfire",
+        "wx.alert.severe_thunderstorm_warning",
+        "quake.usgs_quake",
+        "hydro.00060.usgs.13162225",
+    ])
+    def test_msgid_shape_is_id_colon_category(
+        self, sample_geo: Geo, sample_config: Config, category: str
+    ) -> None:
+        """Every wrap_event call returns msg_id == ``f'{id}:{category}'``.
+
+        Covers both multi-class adapters (where the discriminator is
+        load-bearing) and single-class adapters (where it's a no-op for
+        dedup but still consistent shape across the codebase).
+        """
+        event = Event(
+            id=f"test:{category}:42",
+            adapter="test",
+            category=category,
+            time=datetime(2026, 6, 7, 6, 25, 5, tzinfo=timezone.utc),
+            severity=1,
+            geo=sample_geo,
+            data={},
+        )
+        _, msg_id = wrap_event(event, sample_config)
+        assert msg_id == f"{event.id}:{category}"
+
     def test_extension_attributes_lowercase(
         self, sample_event: Event, sample_config: Config
     ) -> None: