## Summary
- make the builtin MCP config test derive the expected `--codex-home`
argument from `AbsolutePathBuf`
## Why
`AbsolutePathBuf::try_from("/tmp/codex-home")` is rendered as
`D:\\tmp\\codex-home` on Windows, but the test asserted the Unix literal
`"/tmp/codex-home"`. That made the Windows Bazel job fail even though
the production code was behaving correctly.
## Impact
This keeps the test cross-platform while preserving the same transport
assertion on Unix and Windows.
## Validation
- `cargo test -p codex-builtin-mcps`
Co-authored-by: Codex <noreply@openai.com>
