stderr is not seen if command exits with success

What version of Codex is running?

0.19.0

Which model were you using?

gpt5

What platform is your computer?

macos

What steps can reproduce the bug?

Create a script that outputs to stdout and to stderr, but exits with status code 0. Ask codex to run the script and show the output.

#!/usr/bin/env bash

# Minimal repro: prints only to stderr and exits 0
echo "stderr: hidden on success" >&2
exit 0

Many tools - for example Rust's cargo clippy - will exit with success if there are no errors, but still output warnings to stderr. At the moment, if you ask codex to "run clippy and fix all warnings", it will report that there's nothing to fix even if warnings are reported.

What is the expected behavior?

I expect stdout and stderr to always be merged in command execution.

What do you see instead?

Codex sees no stderr output if the script succeeds.

Additional information

_No response_