fix(server): prevent stdio transport from closing original stdio handles

[goingforstudying-ctrl]

Description

When using , the context manager wraps and in . When these wrappers are closed (either explicitly or when exiting the context), they also close the underlying buffers, causing subsequent stdio operations to fail with .

Changes

This PR duplicates the file descriptors before wrapping them using , so that the original stdin/stdout remain open after the transport is closed.

Before (problem):

After (fixed):

Technical Details

• Uses to create duplicate file descriptors
• Opens duplicates with with
• Wraps the duplicates in and
• Original stdin/stdout remain unaffected when transport closes

Fixes #1933

/cc @maintainers

[goingforstudying-ctrl]

Hi @jspahrsummers, just checking in on this PR. Please let me know if any changes are needed. Happy to address any feedback!

[goingforstudying-ctrl]

Hi @maintainer, just checking in on this PR. Please let me know if any changes are needed. Happy to address any feedback!

[goingforstudying-ctrl]

Hi @maintainer, just checking in on this PR. Please let me know if any changes are needed. Happy to address any feedback!

[goingforstudying-ctrl]

Hi @jspahrsummers and team,

Just checking in on this PR again. It's been a few days since the last ping. The fix prevents stdio transport from closing original stdio handles, which could cause issues for consumers that need to continue using stdin/stdout after the MCP client/server shuts down.

Please let me know if:

• Any changes are needed to the implementation
• More context or test cases would help
• There's anything I can do to move this forward

Happy to address any feedback. Thanks!

[goingforstudying-ctrl]

Fixed! Added the missing to — the exception was referenced but wasn't imported. This should resolve the pre-commit / test failures. Please let me know if anything else is needed.

[goingforstudying-ctrl]

Fixed! Added the missing import io to src/mcp/server/stdio.py — the io.UnsupportedOperation exception was referenced but io wasn't imported. This should resolve the pre-commit / test failures. Please let me know if anything else is needed.

[goingforstudying-ctrl]

Fixed the import order issue — wanted before (isort rule). The pre-commit failure was just a formatting fix, not a logic error. All tests pass. Ready for another look when you have a moment!