fix(gateway): per-server lock in OpcConnectionPool to avoid duplicate connects

tests/unit/connection/test_pool.py

@@ -1,3 +1,4 @@
+import asyncio
 from unittest.mock import AsyncMock, MagicMock, patch
 
 import pytest
@@ -86,6 +87,10 @@ async def test_release_idle_evicts_and_disconnects():
 
     fake_client.disconnect.assert_awaited_once()
     assert 'srv' not in pool._connections
+    pool.emit_metric.assert_any_await(
+        metric_object=metrics.OPC_DISCONNECTIONS_TOTAL,
+        tags={'pod_id': pool.pod_id, 'server_name': 'srv'},
+    )
 
 
 @pytest.mark.asyncio
@@ -131,3 +136,50 @@ async def test_release_idle_disconnect_retries_then_gives_up():
 
     assert fake_client.disconnect.await_count == 5
     assert 'srv' not in pool._connections
+
+
+@pytest.mark.asyncio
+async def test_success_path_emits_connection_metrics():
+    pool = make_pool()
+    fake_client = AsyncMock()
+    with patch('ingestor.connection.pool.Client', return_value=fake_client):
+        await pool.get('srv', {'url': 'opc.tcp://h:4840', 'use_security': False})
+
+    pool.emit_metric.assert_any_await(
+        metric_object=metrics.OPC_CONNECTIONS_TOTAL,
+        tags={'pod_id': pool.pod_id, 'server_name': 'srv'},
+    )
+    pool.emit_metric.assert_any_await(
+        metric_object=metrics.OPC_CONNECTION_STATUS,
+        method='set',
+        value=1,
+        tags={'pod_id': pool.pod_id, 'server_name': 'srv', 'server_url': 'opc.tcp://h:4840'},
+    )
+
+
+@pytest.mark.asyncio
+async def test_concurrent_get_same_server_connects_once():
+    pool = make_pool()
+    started = asyncio.Event()
+    proceed = asyncio.Event()
+
+    clients = [AsyncMock(), AsyncMock()]
+
+    async def slow_connect():
+        started.set()
+        await proceed.wait()
+
+    clients[0].connect.side_effect = slow_connect
+
+    cfg = {'url': 'opc.tcp://h:4840', 'use_security': False}
+    with patch('ingestor.connection.pool.Client', side_effect=clients) as ctor:
+        t1 = asyncio.create_task(pool.get('srv', cfg))
+        await started.wait()  # t1 is mid-connect, holding the per-server lock
+        t2 = asyncio.create_task(pool.get('srv', cfg))
+        await asyncio.sleep(0)  # let t2 block on the lock (not build a 2nd Client)
+        proceed.set()
+        c1, c2 = await asyncio.gather(t1, t2)
+
+    assert c1 is c2 is clients[0]
+    assert ctor.call_count == 1
+    assert clients[0].connect.await_count == 1