functions.shell tool-level timeout aborts inner shell timeout; returns "command timed out" instead of inner exit code

What version of Codex is running?

codex-cli 0.20.0

Which model were you using?

N/A (issue about CLI helper)

What platform is your computer?

Linux 6.14.3-x86_64-linode168 x86_64 unknown

What steps can reproduce the bug?

1. Run a command via the agent's functions.shell helper that itself uses shell-level timeout, for example:

`bash -lc 'timeout 20s sleep 1000; echo exit_code:$?'

1. Invoke the agent with a tool-level timeout <= 20s (or let the agent default be <= 20s).
2. Observe the agent returns a "command timed out" error and the inner echo exit_code:$? is not printed.

Example agent-like call (pseudocode):
functions.shell({"command":["bash","-lc","timeout 20s sleep 1000; echo exit_code:$?"], "timeout": 15})

What is the expected behavior?

If the inner command handles its own timeout via shell timeout, and the agent-level timeout is larger, the agent should allow the inner timeout to finish and surface the inner exit code (e.g., 124) and any stdout/stderr emitted before termination. If the agent-level timeout kills the whole call, the agent should clearly indicate agent-level termination and, if possible, preserve the inner process termination code/signal.

What do you see instead?

The agent returns a generic command timed out from the tooling layer and does not expose the inner timeout exit code or the echo exit_code:$? output.

Additional information

• Typical coreutils timeout exit codes: 124 (timed out), 125 (timeout error), 137 (killed by SIGKILL).
• Submitted via Codex CLI (automated agent) — please include this note when triaging.