fix(agent): prevent AsyncOpenAI/httpx cross-loop deadlock in gateway mode (#2701)

In gateway mode, async tools (vision_analyze, web_extract, session_search)
deadlock because _run_async() spawns a thread with asyncio.run(), creating
a new event loop, but _get_cached_client() returns an AsyncOpenAI client
bound to a different loop. httpx.AsyncClient cannot work across event loop
boundaries, causing await client.chat.completions.create() to hang forever.

Fix: include the event loop identity in the async client cache key so each
loop gets its own AsyncOpenAI instance. Also fix session_search_tool.py
which had its own broken asyncio.run()-in-thread pattern — now uses the
centralized _run_async() bridge.

agent/auxiliary_client.py

@@ -1258,13 +1258,33 @@ def _get_cached_client(
     base_url: str = None,
     api_key: str = None,
 ) -> Tuple[Optional[Any], Optional[str]]:
-    """Get or create a cached client for the given provider."""
-    cache_key = (provider, async_mode, base_url or "", api_key or "")
+    """Get or create a cached client for the given provider.
+
+    Async clients (AsyncOpenAI) use httpx.AsyncClient internally, which
+    binds to the event loop that was current when the client was created.
+    Using such a client on a *different* loop causes deadlocks or
+    RuntimeError.  To prevent cross-loop issues (especially in gateway
+    mode where _run_async() may spawn fresh loops in worker threads), the
+    cache key for async clients includes the current event loop's identity
+    so each loop gets its own client instance.
+    """
+    # Include loop identity for async clients to prevent cross-loop reuse.
+    # httpx.AsyncClient (inside AsyncOpenAI) is bound to the loop where it
+    # was created — reusing it on a different loop causes deadlocks (#2681).
+    loop_id = 0
+    current_loop = None
+    if async_mode:
+        try:
+            import asyncio as _aio
+            current_loop = _aio.get_event_loop()
+            loop_id = id(current_loop)
+        except RuntimeError:
+            pass
+    cache_key = (provider, async_mode, base_url or "", api_key or "", loop_id)
     with _client_cache_lock:
         if cache_key in _client_cache:
             cached_client, cached_default, cached_loop = _client_cache[cache_key]
             if async_mode:
-                # Async clients are bound to the event loop that created them.
                 # A cached async client whose loop has been closed will raise
                 # "Event loop is closed" when httpx tries to clean up its
                 # transport.  Discard the stale client and create a fresh one.
@@ -1286,13 +1306,7 @@ def _get_cached_client(
     if client is not None:
         # For async clients, remember which loop they were created on so we
         # can detect stale entries later.
-        bound_loop = None
-        if async_mode:
-            try:
-                import asyncio as _aio
-                bound_loop = _aio.get_event_loop()
-            except RuntimeError:
-                pass
+        bound_loop = current_loop
         with _client_cache_lock:
             if cache_key not in _client_cache:
                 _client_cache[cache_key] = (client, default_model, bound_loop)