Codex Exec — one-shot runtime adapter

Run exactly one caller-supplied Codex prompt and capture its result. This skill does not choose work, retry failures, validate by itself, or control continuation.

One prompt, one process, one captured artifact is what makes the run auditable: when nothing loops, every byte of output traces to exactly one invocation, and a disagreement about what happened is settled by the artifact.

Named failure mode — stdin hang: a non-TTY run left waiting forever on an open stdin nobody will write to; always pipe the prompt or close the stream.

Anti-pattern: granting workspace-write or network access "in case the prompt needs it". Corrective: match the sandbox to the declared effects; a review prompt runs read-only, full stop.

Procedure

1. Confirm the intended executable, profile, and caller-supplied prompt.
2. Set the working root explicitly with -C.
3. Match the sandbox to the requested effects: read-only for offline review, workspace-write for authorized edits, and broader access only when the caller explicitly requires network or external effects.
4. Use scripts/lib/codex-exec.sh and codex_exec_guarded. Pipe the prompt, provide a prompt file/argument, or close stdin in non-TTY execution.
5. Supply CODEX_EXEC_TIMEOUT as positive finite seconds or inherit an absolute CODEX_EXEC_DEADLINE_EPOCH. There is no fixed ten-minute default: without an explicit timeout, use the deadline's remaining time; with both, the earlier bound wins, including capability probes and prompt preparation. Pass the same deadline to successive calls; a new invocation cannot renew it. Missing both bounds, or empty, zero, negative or malformed explicit values, prevents launch. An expired deadline times out before dispatch.
6. Capture stdout with CODEX_EXEC_OUT_FILE and optionally separate stderr with CODEX_EXEC_STDERR_FILE. CODEX_EXEC_MAX_OUTPUT_BYTES defaults to 10 MiB (10485760 bytes) and must be a positive finite integer. It caps stdout and stderr combined; file-prompt copies and AGY/local-mlx stdin preparation each use the same cap. Capture sinks must be regular files (or /dev/null). Reviewer workspace writes, including files it writes with -o, are outside this capture cap.
7. Report the typed run result, then stop: the process exit status, the captured artifact path, the timeout/deadline and capture cap applied, and whether cleanup was triggered. Cancellation is the caller's; this skill neither retries nor continues on its own.

The supported host must have /usr/bin/perl with its core POSIX, IO::Select, Fcntl, and Time::HiRes modules, a monotonic clock, process-group signalling, and a resolved timeout/gtimeout supporting --foreground. Missing capability fails closed. The embedded adapter mechanism establishes one owned process group before launching the reviewer. It sends TERM then KILL after 200 ms on expiry, cancellation, excess output, or direct-parent exit; it bounds pipe draining to a further short cleanup window rather than waiting indefinitely for descendants to close inherited pipes. This includes ordinary descendants left by a successful parent and TERM-resistant children. It does not promise cleanup of processes that deliberately escape the owned group or session. Group members remaining after direct-parent exit are reported as rep-survivor (exit 122): the run remains degraded even when cleanup subsequently succeeds. After its cleanup window the adapter checks whether the owned group still exists. Remaining membership, including zombies it cannot independently reap, is reported as CLEANUP-UNVERIFIED (exit 2), never successful cleanup.

CODEX_EXEC_WRAP remains Codex-only: the sealed launch order is wrapper → resolved timeout → reviewer, with Codex's sandbox bypass only when the external wrapper supplies the sandbox. The capture/cleanup supervisor runs outside that sealed launch. No process-wide file-size limit restricts reviewer work products.

Terminal outcomes are explicit: unavailable/invalid limits → 2; descendants left after direct-parent exit → 122; capture/input limit → 123; deadline expiry or empty consumed output → 124; prompt echo → 125; cancellation → 128 + signal number. Other genuine reviewer exit codes are preserved. These reserved codes describe runtime evidence, never a semantic verdict. On timeout, cancellation, or excess output, partial capture stays in caller-provided files; an adapter-owned output sink is streamed before removal. Failed prompt preparation reports its preserved partial input path. The caller decides whether to launch another invocation.

Example

# REVIEW_TIMEOUT_SECONDS is selected by the caller. Alternatively export
# CODEX_EXEC_DEADLINE_EPOCH once and omit CODEX_EXEC_TIMEOUT below; retain
# that same absolute deadline for every invocation in its scope.
. "$AGENTOPS_ROOT/scripts/lib/codex-exec.sh"
CODEX_EXEC_DIR="$WORKSPACE" CODEX_EXEC_SANDBOX=read-only \
CODEX_EXEC_PROMPT_ARG="$PROMPT" CODEX_EXEC_TIMEOUT="$REVIEW_TIMEOUT_SECONDS" \
CODEX_EXEC_MAX_OUTPUT_BYTES=10485760 CODEX_EXEC_OUT_FILE="$OUTPUT" \
  codex_exec_guarded </dev/null

For a validator, the prompt must name the acceptance digest, exact subject manifest digest, author context ID, evidence, and required checked/not-checked report. The validator context ID must be distinct from the author's before a PASS verdict is possible. When the caller elects a cross-model fresh validator, record model identities per the agent-native model-dispatch recipe and match the sandbox to declared effects.