Summary
- delete the deprecated stdio transport plumbing from the exec server
stack
- add a basic `exec_server()` harness plus test utilities to start a
server, send requests, and await events
- refresh exec-server dependencies, configs, and documentation to
reflect the new flow
Testing
- Not run (not requested)
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Co-authored-by: starr-openai <starr@openai.com>
Co-authored-by: Codex <noreply@openai.com>
