M8-R01: add configurable MQTT client identity

tests/test_dsmr_subscription_apply.py

@@ -3,6 +3,7 @@
 from __future__ import annotations
 
 from dataclasses import replace
+from types import SimpleNamespace
 
 import pytest
 
@@ -44,6 +45,7 @@ def fake_mqtt(monkeypatch):
     fake = _FakeMqtt()
     monkeypatch.setattr("app.integrations.mqtt.mqtt_manager", fake)
     monkeypatch.setattr(dsmr_ingest, "_subscriptions", {})
+    monkeypatch.setattr(dsmr_ingest, "_subscription_client_ids", {})
     monkeypatch.setattr(dsmr_ingest, "_tariffs", {})
     return fake
 
@@ -81,6 +83,18 @@ def test_same_snapshot_has_no_subscription_churn(fake_mqtt, monkeypatch):
     assert fake_mqtt.remove_calls == []
 
 
+def test_changed_base_client_id_replaces_all_enabled_sources(fake_mqtt, monkeypatch):
+    snapshot = _source(1, "topic", broker_host="broker.test")
+    monkeypatch.setattr(dsmr_ingest, "_enabled_snapshots", lambda: [snapshot])
+
+    dsmr_ingest.apply_dsmr_subscription(SimpleNamespace(mqtt_client_id="home-automation"))
+    dsmr_ingest.apply_dsmr_subscription(SimpleNamespace(mqtt_client_id="home-automation-dev"))
+
+    assert fake_mqtt.remove_calls == [1]
+    assert [source_id for source_id, _ in fake_mqtt.replace_calls] == [1, 1]
+    assert fake_mqtt.replace_calls[-1][1]["base_client_id"] == "home-automation-dev"
+
+
 def test_same_topic_on_different_brokers_is_allowed(fake_mqtt, monkeypatch):
     monkeypatch.setattr(
         dsmr_ingest,