SIENTIAPDE-1646

Add tests for retrain, drift, storage, OPC repo, worker paths

- covers csv lookup fallback, drift insufficient-data passthrough,
  timestamp tz normalization, storage close without engine, OPC
  watchdog/write_value fallbacks and reconnect reporting, and
  legacy runtime install in worker main

tests/laborious/worker/test_worker.py

@@ -248,3 +248,45 @@ async def test_main_worker_gather_error_exits_one(monkeypatch):
             await worker.main()
 
     assert m_logger.return_value.custom_error.called
+
+
+@mark.asyncio
+async def test_main_legacy_runtime_installs_single(monkeypatch):
+    """The `legacy` runtime is served by the `single` store runtime."""
+    monkeypatch.setenv('RUNTIME', 'legacy')
+    fake_plugin = MagicMock()
+    fake_plugin.install_runtime = AsyncMock(side_effect=RuntimeError('stop after install'))
+    with (
+        patch('laborious.worker.worker.start_prometheus_server'),
+        patch('laborious.worker.worker.get_logger'),
+        patch(
+            'laborious.worker.worker.build_mongodb_config',
+            return_value={'connection_string': 'cs', 'database_name': 'db'},
+        ),
+        patch('laborious.worker.worker.NotificationHandler'),
+        patch('laborious.worker.worker.MetricsController'),
+        patch(
+            'laborious.worker.worker.build_plugin_store_config',
+            return_value={
+                'base_url': '',
+                'owner': '',
+                'repo': '',
+                'username': None,
+                'password': None,
+                'branch': None,
+                'cache_ttl_seconds': None,
+                'pypi_index_url': '',
+                'pypi_username': None,
+                'pypi_password': None,
+            },
+        ),
+        patch('laborious.worker.worker.PluginStore', return_value=fake_plugin),
+        patch.object(worker.metrics.APP_UP, 'labels') as labels,
+        patch('laborious.worker.worker.sys.exit', side_effect=SystemExit(1)),
+    ):
+        labels.return_value = MagicMock()
+        with raises(SystemExit):
+            await worker.main()
+
+    fake_plugin.install_runtime.assert_awaited_once()
+    assert fake_plugin.install_runtime.await_args.kwargs['runtime_name'] == 'single'