Local MCP wouldn't start on windows / git bash

[intval]

Describe the bug
Subprocess (MCP) wouldn't start.. Asyncio not implement error

2025-06-11 22:35:02,328 - ERROR - fast_api.py:788 - Error in event_generator: 
Traceback (most recent call last):
  File "B:\code\gen1\backend\.venv\Lib\site-packages\mcp\client\stdio\win32.py", line 72, in create_windows_process
    process = await anyio.open_process(
              ^^^^^^^^^^^^^^^^^^^^^^^^^
    ...<8 lines>...
    )
    ^
  File "B:\code\gen1\backend\.venv\Lib\site-packages\anyio\_core\_subprocesses.py", line 190, in open_process
    return await get_async_backend().open_process(
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    ...<11 lines>...
    )
    ^
  File "B:\code\gen1\backend\.venv\Lib\site-packages\anyio\_backends\_asyncio.py", line 2561, in open_process
    process = await asyncio.create_subprocess_exec(
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    ...<5 lines>...
    )
    ^
  File "C:\Users\spc\AppData\Roaming\uv\python\cpython-3.13.3-windows-x86_64-none\Lib\asyncio\subprocess.py", line 224, in create_subprocess_exec
    transport, protocol = await loop.subprocess_exec(
                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^
    ...<3 lines>...
        stderr=stderr, **kwds)
        ^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\spc\AppData\Roaming\uv\python\cpython-3.13.3-windows-x86_64-none\Lib\asyncio\base_events.py", line 1788, in subprocess_exec
    transport = await self._make_subprocess_transport(
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        protocol, popen_args, False, stdin, stdout, stderr,
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        bufsize, **kwargs)
        ^^^^^^^^^^^^^^^^^^
  File "C:\Users\spc\AppData\Roaming\uv\python\cpython-3.13.3-windows-x86_64-none\Lib\asyncio\base_events.py", line 533, in _make_subprocess_transport
    raise NotImplementedError
NotImplementedError

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "B:\code\gen1\backend\.venv\Lib\site-packages\google\adk\cli\fast_api.py", line 777, in event_generator
    async for event in runner.run_async(
    ...<8 lines>...
      yield f"data: {sse_event}\n\n"
  File "B:\code\gen1\backend\.venv\Lib\site-packages\google\adk\runners.py", line 197, in run_async
    async for event in invocation_context.agent.run_async(invocation_context):
    ...<2 lines>...
      yield event
  File "B:\code\gen1\backend\.venv\Lib\site-packages\google\adk\agents\base_agent.py", line 147, in run_async
    async for event in self._run_async_impl(ctx):
      yield event
  File "B:\code\gen1\backend\.venv\Lib\site-packages\google\adk\agents\llm_agent.py", line 278, in _run_async_impl
    async for event in self._llm_flow.run_async(ctx):
      self.__maybe_save_output_to_state(event)
      yield event
  File "B:\code\gen1\backend\.venv\Lib\site-packages\google\adk\flows\llm_flows\base_llm_flow.py", line 282, in run_async
    async for event in self._run_one_step_async(invocation_context):
      last_event = event
      yield event
  File "B:\code\gen1\backend\.venv\Lib\site-packages\google\adk\flows\llm_flows\base_llm_flow.py", line 302, in _run_one_step_async
    async for event in self._preprocess_async(invocation_context, llm_request):
      yield event
  File "B:\code\gen1\backend\.venv\Lib\site-packages\google\adk\flows\llm_flows\base_llm_flow.py", line 340, in _preprocess_async
    for tool in await agent.canonical_tools(
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        ReadonlyContext(invocation_context)
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    ):
    ^
  File "B:\code\gen1\backend\.venv\Lib\site-packages\google\adk\agents\llm_agent.py", line 367, in canonical_tools
    resolved_tools.extend(await _convert_tool_union_to_tools(tool_union, ctx))
                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "B:\code\gen1\backend\.venv\Lib\site-packages\google\adk\agents\llm_agent.py", line 114, in _convert_tool_union_to_tools
    return await tool_union.get_tools(ctx)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "B:\code\gen1\backend\.venv\Lib\site-packages\google\adk\tools\mcp_tool\mcp_session_manager.py", line 110, in wrapper
    return await func(self, *args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "B:\code\gen1\backend\.venv\Lib\site-packages\google\adk\tools\mcp_tool\mcp_toolset.py", line 138, in get_tools
    self._session = await self._mcp_session_manager.create_session()
                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "B:\code\gen1\backend\.venv\Lib\site-packages\google\adk\tools\mcp_tool\mcp_session_manager.py", line 208, in create_session
    transports = await self._exit_stack.enter_async_context(client)
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\spc\AppData\Roaming\uv\python\cpython-3.13.3-windows-x86_64-none\Lib\contextlib.py", line 668, in enter_async_context
    result = await _enter(cm)
             ^^^^^^^^^^^^^^^^
  File "C:\Users\spc\AppData\Roaming\uv\python\cpython-3.13.3-windows-x86_64-none\Lib\contextlib.py", line 214, in __aenter__
    return await anext(self.gen)
           ^^^^^^^^^^^^^^^^^^^^^
  File "B:\code\gen1\backend\.venv\Lib\site-packages\mcp\client\stdio\__init__.py", line 115, in stdio_client
    process = await _create_platform_compatible_process(
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    ...<9 lines>...
    )
    ^
  File "B:\code\gen1\backend\.venv\Lib\site-packages\mcp\client\stdio\__init__.py", line 230, in _create_platform_compatible_process
    process = await create_windows_process(command, args, env, errlog, cwd)
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "B:\code\gen1\backend\.venv\Lib\site-packages\mcp\client\stdio\win32.py", line 85, in create_windows_process
    process = await anyio.open_process(
              ^^^^^^^^^^^^^^^^^^^^^^^^^
        [command, *args], env=env, stderr=errlog, cwd=cwd
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    )
    ^
  File "B:\code\gen1\backend\.venv\Lib\site-packages\anyio\_core\_subprocesses.py", line 190, in open_process
    return await get_async_backend().open_process(
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    ...<11 lines>...
    )
    ^
  File "B:\code\gen1\backend\.venv\Lib\site-packages\anyio\_backends\_asyncio.py", line 2561, in open_process
    process = await asyncio.create_subprocess_exec(
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    ...<5 lines>...
    )
    ^
  File "C:\Users\spc\AppData\Roaming\uv\python\cpython-3.13.3-windows-x86_64-none\Lib\asyncio\subprocess.py", line 224, in create_subprocess_exec
    transport, protocol = await loop.subprocess_exec(
                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^
    ...<3 lines>...
        stderr=stderr, **kwds)
        ^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\spc\AppData\Roaming\uv\python\cpython-3.13.3-windows-x86_64-none\Lib\asyncio\base_events.py", line 1788, in subprocess_exec
    transport = await self._make_subprocess_transport(
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        protocol, popen_args, False, stdin, stdout, stderr,
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        bufsize, **kwargs)
        ^^^^^^^^^^^^^^^^^^
  File "C:\Users\spc\AppData\Roaming\uv\python\cpython-3.13.3-windows-x86_64-none\Lib\asyncio\base_events.py", line 533, in _make_subprocess_transport
    raise NotImplementedError
NotImplementedError

To Reproduce
(Copied from the docs as is)

agent = LlmAgent(
    model=MODEL,
    name="capital_agent_tool",
    description="Retrieves the capital city using a specific tool.",
    instruction=get_instructions(),
    tools=[
        MCPToolset(
            connection_params=StdioServerParameters(
                command='python',
                args=[
                    "-y",  # Argument for npx to auto-confirm install
                    "@modelcontextprotocol/server-filesystem",
                    # IMPORTANT: This MUST be an ABSOLUTE path to a folder the
                    # npx process can access.
                    # Replace with a valid absolute path on your system.
                    # For example: "/Users/youruser/accessible_mcp_files"
                    # or use a dynamically constructed absolute path:
                    os.path.abspath("/c/Users/spc/mcp-googledocs-server"),
                ],
            ),
            # Optional: Filter which tools from the MCP server are exposed
            # tool_filter=['list_directory', 'read_file']
        )
    ],
    output_key="expose_result"
)

Expected behavior
Starts npx process

Desktop (please complete the following information):

• OS: windows 11
• Python version(python -V): cpython-3.13.3-windows-x86_64-none
• ADK version: 1.2.1
• Git Bash on windows

[sumansuhag]

File "asyncio\base_events.py", line 533, in _make_subprocess_transport
raise NotImplementedError
asyncio.create_subprocess_exec is not fully supported in Git Bash

Patch workaround (only)

import anyio
from anyio._backends._asyncio import open_process as patched_open_process

async def dummy_open_process(*args, **kwargs):
raise RuntimeError("asyncio subprocess not supported in this terminal. Try PowerShell.")

anyio.open_process = patched_open_process

[intval]

Doesn't work on powershell or command line either.
Root cause: modelcontextprotocol/python-sdk#596

[intval]

I've also found out
fastapi/fastapi#7770

Turns out it happens only when --reload is enabled in fastapi. When running adk web with --no-reload this error doesn't appear.