Joonsoo Lee f828cd2897 fix: resolve Windows MCP server execution for script-based tools (#3828) ...

## What?

Fixes MCP server initialization failures on Windows when using
script-based tools like `npx`, `pnpm`, and `yarn` that rely on
`.cmd`/`.bat` files rather than `.exe` binaries.

Fixes #2945

## Why?

Windows users encounter "program not found" errors when configuring MCP
servers with commands like `npx` in their `~/.codex/config.toml`. This
happens because:

- Tools like `npx` are batch scripts (`npx.cmd`) on Windows, not
executable binaries
- Rust's `std::process::Command` bypasses the shell and cannot execute
these scripts directly
- The Windows shell normally handles this by checking `PATHEXT` for
executable extensions

Without this fix, Windows users must specify full paths or add `.cmd`
extensions manually, which breaks cross-platform compatibility.

## How?

Added platform-specific program resolution using the `which` crate to
find the correct executable path:

- **Windows**: Resolves programs through PATH/PATHEXT to find
`.cmd`/`.bat` scripts
- **Unix**: Returns the program unchanged (no-op, as Unix handles
scripts natively)

### Changes

- Added `which = "6"` dependency to `mcp-client/Cargo.toml`
- Implemented `program_resolver` module in `mcp_client.rs` with
platform-specific resolution
- Added comprehensive tests for both Windows and Unix behavior

### Testing

Added platform-specific tests to verify:
- Unix systems execute scripts without extensions
- Windows fails without proper extensions
- Windows succeeds with explicit extensions
- Cross-platform resolution enables successful execution

**Tested on:**
- Windows 11 (NT 10.0.26100.0 x64)
- PowerShell 5.1 & 7+, CMD, Git Bash
- MCP servers: playwright, context7, supabase
- WSL (verified no regression)

**Local checks passed:**
```bash
cargo test && cargo clippy --tests && cargo fmt -- --config imports_granularity=Item
```

### Results

**Before:**
```
🖐 MCP client for `playwright` failed to start: program not found
```

**After:**
```
🖐 MCP client for `playwright` failed to start: request timed out
```

Windows users can now use simple commands like `npx` in their config
without specifying full paths or extensions. The timeout issue is a
separate concern that will be addressed in a follow-up PR.

---------

Co-authored-by: Eric Traut <etraut@openai.com>

2025-11-16 13:41:10 -08:00

..

src

fix: resolve Windows MCP server execution for script-based tools (#3828)

2025-11-16 13:41:10 -08:00

tests

[MCP] Add support for resources (#5239)

2025-10-17 01:05:15 -04:00

Cargo.toml

fix: resolve Windows MCP server execution for script-based tools (#3828)

2025-11-16 13:41:10 -08:00