## Why
The post-merge `rust-ci-full` run for #18999 still failed the Ubuntu remote `suite::remote_env` sandboxed filesystem tests. That run checked out merge commit `ddde50c611e4800cb805f243ed3c50bbafe7d011`, so the arg0 guard lifetime fix was present.
The remaining gap is that the remote exec-server can pass an arg0 alias path such as `codex-linux-sandbox` as a runtime helper, but the sandboxed filesystem helper only added the real Codex binary parent as a readable runtime root. When bubblewrap re-enters Codex through the alias path, the alias directory also has to be visible inside the sandbox.
## What Changed
- Track all helper runtime read roots instead of a single root.
- Add both the real Codex executable parent and the `codex-linux-sandbox` alias parent to sandbox readable roots.
- Add unit coverage for the alias-parent root.
## Verification
- `cargo test -p codex-exec-server`
- `just argument-comment-lint -p codex-exec-server`
- `just fix -p codex-exec-server`
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