`/codex:setup --enable-review-gate` reports success but writes the flag to a state root the Stop hook never reads — the gate silently fails open

Summary

/codex:setup --enable-review-gate reports success and returns "reviewGateEnabled": true,
but the flag can be written to a state root that the Stop hook never reads. The gate is
then silently inert: no error, no warning, and setup --json keeps affirming it is on.

The split-root mechanism itself is already described in #636 (broker/SessionEnd). This
issue is a different, user-facing consequence of it: an opt-in review gate that fails
open while reporting that it is armed. #676 covers the gate failing open on malformed
hook stdin; this is the same failure class reached through configuration instead.

Mechanism

scripts/lib/state.mjs:29-43 — the state root depends on CLAUDE_PLUGIN_DATA, with a
$TMPDIR fallback. The slug and hash are identical either way; only the root differs.

The two sides of the gate resolve that root in different environments:

Side	Runs as	CLAUDE_PLUGIN_DATA	State root used
/codex:setup --enable-review-gate	Bash tool	often unset	$TMPDIR/codex-companion/<slug>-<hash>
stop-review-gate-hook.mjs:154	hook, spawned by the harness	set	$CLAUDE_PLUGIN_DATA/state/<slug>-<hash>

The plugin is aware of this and tries to bridge it — session-lifecycle-hook.mjs:80:

function handleSessionStart(input) {
  appendEnvVar(SESSION_ID_ENV, input.session_id);
  appendEnvVar(TRANSCRIPT_PATH_ENV, input.transcript_path);
  appendEnvVar(PLUGIN_DATA_ENV, process.env[PLUGIN_DATA_ENV]);   // <- propagates to the Bash tool
}

But appendEnvVar is a no-op whenever process.env.CLAUDE_ENV_FILE is unset, and the
whole propagation never happens at all if the SessionStart hook did not run. Two
reachable paths to that:

1. Plugin installed mid-session (/plugin install + /reload-plugins). The plugin's
   SessionStart hook never ran for that session, so nothing was ever appended to
   CLAUDE_ENV_FILE. This is exactly the flow a first-time user follows — install the
   plugin, then immediately run /codex:setup, which is what the setup command itself
   instructs. Every Bash invocation for the rest of that session resolves to $TMPDIR.
2. SessionStart killed by its own 5s timeout (#670) — same outcome in an ordinary
   session, not just a mid-session install.

hooks/hooks.json gives Stop a 900s timeout but SessionStart only 5s, so path 2 is
not hypothetical.

Repro

Fresh session, plugin installed mid-session, on macOS, plugin 1.0.6, codex-cli 0.149.1:

$ env | grep -E 'CLAUDE_PLUGIN_DATA|CLAUDE_ENV_FILE|CODEX_COMPANION'
(nothing)

$ node .../scripts/codex-companion.mjs setup --json --enable-review-gate
  "reviewGateEnabled": true,
  "actionsTaken": ["Enabled the stop-time review gate for /Users/me/Projects/alfred-front."],
  "nextSteps": []

Where the flag actually landed:

$ cat "$TMPDIR/codex-companion/alfred-front-790ce51531842df0/state.json"
{ "version": 1, "config": { "stopReviewGate": true }, "jobs": [] }

$ ls ~/.claude/plugins/data/codex-openai-codex/state/
(empty — the root the Stop hook reads has no state at all)

Re-running the same command with the variable set writes a second, independent copy:

$ CLAUDE_PLUGIN_DATA=~/.claude/plugins/data/codex-openai-codex \
    node .../scripts/codex-companion.mjs setup --json --enable-review-gate
  "actionsTaken": ["Enabled the stop-time review gate for /Users/me/Projects/alfred-front."]

$ cat ~/.claude/plugins/data/codex-openai-codex/state/alfred-front-790ce51531842df0/state.json
{ "version": 1, "config": { "stopReviewGate": true }, "jobs": [] }

Same repo, same slug, same hash, two state files, one of them ignored by the hook.

Impact

• The user explicitly opts into a review gate; the gate never fires. Failing open on a
  quality gate is worse than failing closed, and here there is no signal at all.
• setup --json is affirmatively misleading: reviewGateEnabled: true reflects the state
  file the command just wrote, not the one the hook will read.
• The $TMPDIR fallback is purged by macOS, so even a session where the propagation works
  can lose the flag later without the user touching anything.
• --disable-review-gate has the mirror-image problem: it can clear a flag in one root
  while an armed one persists in the other.

Suggested fixes

Roughly in order of cost:

1. Report the resolved path. Add stateFile (and the resolved root) to the setup --json
   payload and to the human-readable output. A one-line change that makes every split-root
   bug in this class self-diagnosing.
2. Warn when the variable is absent. If CLAUDE_PLUGIN_DATA is unset while writing
   config, emit a nextSteps warning rather than silently using $TMPDIR — configuration
   is not throwaway state, unlike job files.
3. Store durable config outside the volatile root. stopReviewGate is small,
   long-lived, per-workspace config; $TMPDIR is the wrong medium for it regardless of
   which root wins. A stable location (e.g. under ~/.codex/) keyed by workspace hash
   removes the divergence for config even if job state stays where it is.
4. Reconcile on read. Have the Stop hook check the fallback root when the primary has
   no state file, and migrate it — also fixes the SessionEnd miss in #636.

Happy to send a PR for (1) and (2) if that direction is useful.

---

🤖 Generated with Claude Code

Start with scripts/lib/state.mjs:29-43, then trace setup, stop-review-gate-hook.mjs:154, and session-lifecycle-hook.mjs:80 to compare state-root resolution when CLAUDE_PLUGIN_DATA is unset. Reproduce the fresh-session case and inspect the setup --json output. Done means setup and the Stop hook use or clearly report the same durable configuration root, with the selected warning or reconciliation behavior covered by validation.