M8-R02: report DSMR MQTT source health

tests/test_dsmr_subscription_apply.py

@@ -46,6 +46,7 @@ def fake_mqtt(monkeypatch):
     monkeypatch.setattr("app.integrations.mqtt.mqtt_manager", fake)
     monkeypatch.setattr(dsmr_ingest, "_subscriptions", {})
     monkeypatch.setattr(dsmr_ingest, "_subscription_client_ids", {})
+    monkeypatch.setattr(dsmr_ingest, "_subscription_tokens", {})
     monkeypatch.setattr(dsmr_ingest, "_tariffs", {})
     return fake
 
@@ -186,3 +187,17 @@ def test_same_snapshot_aba_rejects_retained_handler(fake_mqtt, monkeypatch):
     old_handler(b"stale")  # type: ignore[operator]
     fake_mqtt.handlers[1]["same"](b"fresh")  # type: ignore[operator]
     assert received == [(b"fresh", snapshot)]
+
+
+def test_source_state_handler_is_generation_scoped(fake_mqtt, monkeypatch):
+    snapshot = _source(1, "same", broker_host="one.test")
+    monkeypatch.setattr(dsmr_ingest, "_enabled_snapshots", lambda: [snapshot])
+    dsmr_ingest.apply_dsmr_subscription()
+    stale = fake_mqtt.replace_calls[-1][1]["state_handler"]
+    monkeypatch.setattr(dsmr_ingest, "_enabled_snapshots", lambda: [])
+    dsmr_ingest.apply_dsmr_subscription()
+    monkeypatch.setattr(dsmr_ingest, "_enabled_snapshots", lambda: [snapshot])
+    dsmr_ingest.apply_dsmr_subscription()
+
+    monkeypatch.setattr(dsmr_ingest, "get_session_local", lambda: (_ for _ in ()).throw(AssertionError()))
+    stale("error")  # type: ignore[operator]