fix: Fix error handling when MCP server is unreachable

Currently ADK web hangs and logs "AGSI callable returned without completing response" when the server is unreachable. To fix, set timeouts for connecting to server.

Co-authored-by: Kathy Wu <wukathy@google.com>
PiperOrigin-RevId: 828648928

src/google/adk/tools/mcp_tool/mcp_session_manager.py

@@ -339,38 +339,50 @@ class MCPSessionManager:
 
       # Create a new session (either first time or replacing disconnected one)
       exit_stack = AsyncExitStack()
+      timeout_in_seconds = (
+          self._connection_params.timeout
+          if hasattr(self._connection_params, 'timeout')
+          else None
+      )
 
       try:
         client = self._create_client(merged_headers)
 
-        transports = await exit_stack.enter_async_context(client)
-        # The streamable http client returns a GetSessionCallback in addition to the read/write MemoryObjectStreams
-        # needed to build the ClientSession, we limit then to the two first values to be compatible with all clients.
+        transports = await asyncio.wait_for(
+            exit_stack.enter_async_context(client),
+            timeout=timeout_in_seconds,
+        )
+        # The streamable http client returns a GetSessionCallback in addition to the
+        # read/write MemoryObjectStreams needed to build the ClientSession, we limit
+        # then to the two first values to be compatible with all clients.
         if isinstance(self._connection_params, StdioConnectionParams):
           session = await exit_stack.enter_async_context(
               ClientSession(
                   *transports[:2],
-                  read_timeout_seconds=timedelta(
-                      seconds=self._connection_params.timeout
-                  ),
+                  read_timeout_seconds=timedelta(seconds=timeout_in_seconds),
               )
           )
         else:
           session = await exit_stack.enter_async_context(
               ClientSession(*transports[:2])
           )
-        await session.initialize()
+        await asyncio.wait_for(session.initialize(), timeout=timeout_in_seconds)
 
         # Store session and exit stack in the pool
         self._sessions[session_key] = (session, exit_stack)
         logger.debug('Created new session: %s', session_key)
         return session
 
-      except Exception:
+      except Exception as e:
         # If session creation fails, clean up the exit stack
         if exit_stack:
-          await exit_stack.aclose()
-        raise
+          try:
+            await exit_stack.aclose()
+          except Exception as exit_stack_error:
+            logger.warning(
+                'Error during session creation cleanup: %s', exit_stack_error
+            )
+        raise ConnectionError(f'Failed to create MCP session: {e}') from e
 
   async def close(self):
     """Closes all sessions and cleans up resources."""