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

ingestor/connection/pool.py

@@ -29,6 +29,9 @@ class OpcConnectionPool(SientiaMonitoring):
         self.metadata = metadata or {}
         self.clock = MonotonicClock()
         self._connections: dict[str, tuple[Client, float]] = {}
+        # ponytail: one Lock per server_id, never cleaned up — server set is
+        # small and bounded. Add eviction of stale locks only if it grows.
+        self._locks: dict[str, asyncio.Lock] = {}
 
         SientiaMonitoring.__init__(
             self,
@@ -38,13 +41,28 @@ class OpcConnectionPool(SientiaMonitoring):
         )
 
     async def get(self, server_id: str, server_cfg: dict) -> Client:
-        """Return the cached client for `server_id`, connecting one if needed."""
-        cached = self._connections.get(server_id)
-        if cached is not None:
-            client, _ = cached
-            self._connections[server_id] = (client, self.clock.elapsed())
-            return client
+        """Return the cached client for `server_id`, connecting one if needed.
 
+        Double-checked under a per-server lock so concurrent callers for the
+        same new server share one connection (no leaked, untracked sessions)."""
+        client = self._cached(server_id)
+        if client is not None:
+            return client
+        async with self._locks.setdefault(server_id, asyncio.Lock()):
+            client = self._cached(server_id)  # re-check: a racer may have connected
+            if client is not None:
+                return client
+            return await self._open(server_id, server_cfg)
+
+    def _cached(self, server_id: str) -> Client | None:
+        entry = self._connections.get(server_id)
+        if entry is None:
+            return None
+        client, _ = entry
+        self._connections[server_id] = (client, self.clock.elapsed())
+        return client
+
+    async def _open(self, server_id: str, server_cfg: dict) -> Client:
         try:
             client = await self._connect(server_cfg)
         except Exception: