fix(mcp): support stdio transport on Windows (#7596)

Windows asyncio event loops do not implement add_signal_handler, causing the stdio server to exit before serving requests. Treat signal registration as optional and cover the unsupported-loop path with a regression test.

openbb_platform/extensions/mcp_server/openbb_mcp_server/app/app.py

@@ -942,7 +942,12 @@ async def stdio_main(mcp_server):
         os._exit(0)  # pylint: disable=protected-access
 
     for sig in (signal.SIGINT, signal.SIGTERM):
-        loop.add_signal_handler(sig, signal_handler)
+        try:
+            loop.add_signal_handler(sig, signal_handler)
+        except NotImplementedError:
+            # Windows event loops do not support signal handlers. The MCP client
+            # owns the stdio child process and closes it directly.
+            break
 
     logger.info("Starting OpenBB MCP Server in STDIO mode. Press Ctrl+C to stop.")
 

openbb_platform/extensions/mcp_server/tests/app/test_app.py

@@ -1,5 +1,6 @@
 """Unit tests for app module."""
 
+import asyncio
 from unittest.mock import MagicMock, patch
 
 import pytest
@@ -13,6 +14,7 @@ from openbb_mcp_server.app.app import (
     _read_system_prompt_file,
     _strip_api_prefix,
     create_mcp_server,
+    stdio_main,
 )
 from openbb_mcp_server.models.settings import MCPSettings
 
@@ -56,6 +58,18 @@ def test_read_system_prompt_file(tmp_path):
     assert _read_system_prompt_file("nonexistent.txt") is None
 
 
+@pytest.mark.asyncio
+async def test_stdio_main_runs_when_signal_handlers_are_unsupported():
+    """Windows event loops can serve stdio without registering signal handlers."""
+    loop = asyncio.get_running_loop()
+    mcp_server = MagicMock()
+
+    with patch.object(loop, "add_signal_handler", side_effect=NotImplementedError):
+        await stdio_main(mcp_server)
+
+    mcp_server.run.assert_called_once_with("stdio")
+
+
 @patch("openbb_mcp_server.app.app.process_fastapi_routes_for_mcp")
 @patch("openbb_mcp_server.app.app.CategoryIndex")
 @patch("openbb_mcp_server.app.app.FastMCP.from_fastapi")