## Why
Redirecting stderr on `exec` while closing the lock descriptor suppressed subsequent installer warnings, including the warning that an existing npm-managed Codex installation remains installed.
## What changed
Remove the stderr redirection from `release_install_lock` when closing file descriptor 9. Add a regression test asserting that a noninteractive install succeeds and emits the existing npm installation warning.
GitOrigin-RevId: 5a35ccd9bf62afb99cc949892ec724a01e2d9eee