Codex Background Stdin Close

Codex Background Stdin Close Pattern

Class of task

Use this skill when launching non-interactive Codex CLI execution from Hermes, especially for long-running implementation lanes or quota-burn batches in isolated worktrees.

Trigger conditions

• codex exec ... prints Reading additional input from stdin... and appears to hang.
• < /dev/null, an empty pipe, or PTY launch does not make Codex proceed.
• The task is a background Codex implementation/review lane that should continue while Hermes does other work.
• Multiple Codex lanes are running and duplicate/stale launches must be avoided.

Reliable Hermes launch pattern

1. Put the prompt in a file when it is long:

   cat > /tmp/codex-issue-NNN.md <<'EOF'
   ...self-contained prompt...
   EOF
   

2. Launch Codex as a Hermes-tracked background process, without shell stdin redirection:

   terminal(
     command='codex exec -c model_reasoning_effort="high" --dangerously-bypass-approvals-and-sandbox --cd /path/to/worktree "$(cat /tmp/codex-issue-NNN.md)"',
     background=True,
     notify_on_complete=True,
   )
   

3. Immediately close stdin for the returned session:

   process(action='close', session_id='proc_...')
   

4. Monitor with:

   process(action='poll', session_id='proc_...')
   process(action='log', session_id='proc_...', limit=200)
   

5. If the run remains stuck at the stdin message, kill the Hermes process session and relaunch once with the same pattern. Do not launch duplicates before checking OS-level ps, worktree git state, and logs.

Scope and safety rules

• Use isolated worktrees/clones for each issue lane.
• Verify the issue is status:plan-approved before implementation; otherwise do planning/review only.
• Use --dangerously-bypass-approvals-and-sandbox only when the user has authorized autonomous execution and the worktree scope is isolated. Record the sandbox failure reason, such as bwrap: loopback: Failed RTM_NEWADDR.
• Do not force-push.
• Require final output or handoff to include issue number, branch, commit SHA(s), validation commands/results, push status, issue URL, and blockers.
• On remote/overflow machines, CLI presence and auth files are not enough. Before assigning a Codex burn lane, run a tiny real codex exec smoke through the same login shell/launch path. A worker may have codex --version and ~/.codex/ present but still fail with 401 Unauthorized / Failed to refresh token: refresh token was already used.
• If a remote worker falls back to Codex and produces a branch for an issue that another Codex lane also touched, do not push blindly. First compare commit/file scope against the already-pushed branch and choose one canonical branch/PR; treat the other as a salvage/reference artifact.

Why this exists

In workspace-hub on 2026-04-27, Codex CLI 0.125 repeatedly hung at Reading additional input from stdin... with < /dev/null, printf "" |, and PTY launches. Starting the run as a Hermes background process and explicitly closing stdin with process close allowed it to proceed.