M8-R14: preserve zero DSMR sample interval

tests/test_dsmr_source_migration.py

@@ -12,6 +12,8 @@ from alembic import command
 from alembic.config import Config
 from sqlalchemy import create_engine, event, inspect, text
 
+from app.integrations.meter_sources import sanitize_source_config, validate_source_config
+
 
 def _config(database_url: str) -> Config:
     config = Config("alembic_app.ini")
@@ -108,7 +110,7 @@ def test_populated_revision_14_adopts_dsmr_history_at_revision_16(tmp_path: Path
                     {"key": "DSMR_INGEST_ENABLED", "value": "true", "at": start},
                     {"key": "DSMR_MQTT_TOPIC", "value": "historic/dsmr", "at": start},
                     {"key": "DSMR_TARIFF_TOPIC", "value": "historic/tariff", "at": start},
-                    {"key": "DSMR_SAMPLE_INTERVAL_S", "value": "15", "at": start},
+                    {"key": "DSMR_SAMPLE_INTERVAL_S", "value": "0", "at": start},
                     {"key": "MQTT_BROKER_HOST", "value": "mqtt.example.invalid", "at": start},
                     {"key": "MQTT_BROKER_PORT", "value": "1884", "at": start},
                     {"key": "MQTT_USERNAME", "value": "historic-user", "at": start},
@@ -159,11 +161,14 @@ def test_populated_revision_14_adopts_dsmr_history_at_revision_16(tmp_path: Path
                 text("SELECT id, enabled, config FROM meter_source WHERE kind = 'dsmr_mqtt'")
             ).one()
             assert source.enabled == 1
-            assert json.loads(source.config) == {
+            source_config = json.loads(source.config)
+            assert source_config == {
                 "broker_host": "mqtt.example.invalid", "broker_port": 1884,
                 "username": "historic-user", "password": "historic-password", "tls_enabled": True,
-                "topic": "historic/dsmr", "tariff_topic": "historic/tariff", "sample_interval_s": 15,
+                "topic": "historic/dsmr", "tariff_topic": "historic/tariff", "sample_interval_s": 0,
             }
+            assert validate_source_config("dsmr_mqtt", source_config) == source_config
+            assert sanitize_source_config("dsmr_mqtt", source_config)["sample_interval_s"] == 0
             assert connection.execute(text("SELECT value FROM app_config WHERE key = 'DSMR_MQTT_TOPIC'")).scalar_one() == "historic/dsmr"
             assert dict(connection.execute(text("SELECT key, value FROM app_config")).all()) == config_before
             assert connection.execute(text("SELECT group_concat(telegram_id) FROM dsmr_reading")).scalar_one() == "77,78,77"