fix: Handle ExceptionGroup errors in MCP client cleanup (#8561)

The MCP library internally uses TaskGroup for async operations, which can
raise ExceptionGroup when cleanup fails. This was causing unhandled errors
to propagate in production.

Changes:
- Update cleanup() method in AsyncBaseMCPClient to catch ExceptionGroup
  using except* syntax and log errors at debug level (best-effort cleanup)
- Remove redundant try/except blocks in mcp_manager.py and
  mcp_server_manager.py that incorrectly re-raised cleanup exceptions

Fixes #8560

🐾 Generated with [Letta Code](https://letta.com)

Co-authored-by: letta-code <248085862+letta-code@users.noreply.github.com>
Co-authored-by: Letta <noreply@letta.com>
Co-authored-by: Kian Jones <11655409+kianjones9@users.noreply.github.com>

letta/services/mcp/base_client.py

@@ -109,9 +109,21 @@ class AsyncBaseMCPClient:
             logger.error("MCPClient has not been initialized")
             raise RuntimeError("MCPClient has not been initialized")
 
-    # TODO: still hitting some async errors for voice agents, need to fix
     async def cleanup(self):
-        await self.exit_stack.aclose()
+        """Clean up resources used by the MCP client.
+
+        This method handles ExceptionGroup errors that can occur when closing async context managers
+        (e.g., from the MCP library's internal TaskGroup usage). Cleanup is a best-effort operation
+        and errors are logged but not re-raised to prevent masking the original exception.
+        """
+        try:
+            await self.exit_stack.aclose()
+        except* Exception as eg:
+            # ExceptionGroup can be raised when closing async context managers that use TaskGroup
+            # Log each sub-exception at debug level since cleanup errors are expected in some cases
+            # (e.g., connection already closed, server unavailable)
+            for exc in eg.exceptions:
+                logger.debug(f"MCP client cleanup error (suppressed): {type(exc).__name__}: {exc}")
 
     def to_sync_client(self):
         raise NotImplementedError("Subclasses must implement to_sync_client")

letta/services/mcp_manager.py

@@ -93,12 +93,7 @@ class MCPManager:
             raise e
         finally:
             if mcp_client:
-                try:
-                    await mcp_client.cleanup()
-                except* Exception as eg:
-                    for e in eg.exceptions:
-                        logger.warning(f"Error listing tools for MCP server {mcp_server_name}: {e}")
-                        raise e
+                await mcp_client.cleanup()
 
     @enforce_types
     async def execute_mcp_server_tool(

letta/services/mcp_server_manager.py

@@ -186,11 +186,7 @@ class MCPServerManager:
             raise e
         finally:
             if mcp_client:
-                try:
-                    await mcp_client.cleanup()
-                except Exception as e:
-                    logger.warning(f"Error listing tools for MCP server {mcp_server_id}: {e}")
-                    raise e
+                await mcp_client.cleanup()
 
     @enforce_types
     async def execute_mcp_server_tool(