feat: experimental codex stdio-to-uds subcommand

[bolinfest]

Today, we offer two transport mechanisms for an MCP server: stdio and HTTP.

I have been experimenting with a third, which is UNIX domain socket, because it has the advantages that:

• The UDS can be attached to long-running process, like an HTTP server.
• The UDS can leverage UNIX file permissions to restrict access.

To make it easier to get started with this approach, this introduces an experimental subcommand codex stdio-to-uds that provides an adapter between a UDS and stdio. The idea is that someone could start an MCP server that communicates over /tmp/mcp.sock. Then the user could specify this on the fly like so:

codex --config mcp_servers.example={command="codex",args=["stdio-to-uds","/tmp/mcp.sock"]}

If this approach becomes popular, we could support it directly in our config:

[mcp_servers.example]
# The presence of this property would imply that
# we launch the LSP using `codex stdio-to-uds`.
unix_domain_socket = "/tmp/mcp.sock"

Unfortunately, the Rust standard library does not provide support for UNIX domain sockets on Windows today even though support was added in October 2018 in Windows 10:

rust-lang/rust#56533

To address this, this PR pulls in https://crates.io/crates/uds_windows as a dependency on Windows.

stdio-to-uds/tests/stdio_to_uds.rs is a simple integration test to verify this works on all of our supported platforms.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Guard stdio-to-uds crate for non-Unix builds

The new stdio-to-uds implementation imports std::os::unix::net::UnixStream unconditionally and the CLI always builds this crate. On Windows, the std::os::unix module is absent, so adding this module to the workspace will cause cargo build for the CLI to fail even if the subcommand is never used. Other platform-specific code paths in the repo use #[cfg] guards; similar gating or a stub implementation is needed here to keep non-Unix builds compiling.

Useful? React with 👍 / 👎.

[bolinfest]

@codex review pls

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. 🚀

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[gpeal]

A README for this crate would probably be useful if you expect this to stick around

[bolinfest]

@gpeal good call: I adapted the PR body so it is suitable for the README