feat(review): Codex review default-on across review/ship/plan/docs

Add a shared codexPreflight() helper (constants.ts) that, in one bash
block, reads codex_reviews, sources gstack-codex-probe, checks install +
auth, and echoes a single canonical mode (ready/not_installed/not_authed/
disabled). All Codex resolvers route through it.

- generateCodexPlanReview: opt-in question removed; the outside voice now
  runs automatically (default-on), falling back to a Claude subagent when
  Codex is missing/unauthed. Cross-model tension still gates on user
  approval (sovereignty preserved).
- generateAdversarialStep: probe-based availability (install AND auth),
  distinct not-installed vs not-authed guidance; 200-line structured-review
  threshold unchanged.
- generateCodexDocReview (new, wired via CODEX_DOC_REVIEW): reviews the
  release's docs against the shipped diff range, informational + an explicit
  apply-fixes decision point, never auto-edits.
- autoplan Phase 0.5 now honors codex_reviews=disabled so the switch is
  truly global.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

scripts/resolvers/constants.ts

@@ -56,3 +56,61 @@ export function codexErrorHandling(feature: string): string {
 - Empty response: note and skip
 On any error: continue — ${feature} is informational, not a gate.`;
 }
+
+/**
+ * Shared Codex preflight bash block — the single source of truth for deciding
+ * whether a Codex review pass should run. Used by ADVERSARIAL_STEP,
+ * CODEX_PLAN_REVIEW, and CODEX_DOC_REVIEW so install/auth/config detection
+ * lives in exactly one place.
+ *
+ * Emits ONE self-contained bash block (the caller must place it in a single
+ * fenced block — CLAUDE.md: each block is a fresh shell, so functions sourced
+ * here do NOT persist to later blocks). It:
+ *   1. reads the `codex_reviews` master switch,
+ *   2. sources `gstack-codex-probe`,
+ *   3. runs `command -v codex` (literal — keeps the e2e substring assertion),
+ *      then `_gstack_codex_auth_probe`, then `_gstack_codex_version_check`,
+ *   4. logs the relevant `_gstack_codex_log_event` for each non-ready outcome,
+ *   5. sets ONE canonical mode var and echoes `CODEX_MODE: <mode>` so the agent
+ *      gates later blocks on the echoed value.
+ *
+ * Mode values: `disabled` (config off) | `not_installed` | `not_authed` | `ready`.
+ * The path is host-rewritten at gen-skill-docs time (pathRewrites), so the
+ * literal `~/.claude/skills/gstack` is correct here and becomes `$GSTACK_ROOT`
+ * etc. for non-Claude hosts.
+ *
+ * `disabledBehavior` controls the `disabled`-mode interpretation, which is the
+ * one branch that legitimately differs per caller (D1):
+ *   - `skip-all` (plan / doc reviews): disabled means no extra review step at
+ *     all — skip the section, no Claude fallback.
+ *   - `codex-only` (diff adversarial): disabled gates only the Codex passes; the
+ *     free Claude adversarial subagent still runs.
+ */
+export function codexPreflight(opts: { modeVar?: string; disabledBehavior: 'skip-all' | 'codex-only' }): string {
+  const m = opts.modeVar ?? '_CODEX_MODE';
+  const disabledLine = opts.disabledBehavior === 'codex-only'
+    ? 'Skip the Codex passes only; the Claude adversarial subagent below STILL runs (it is free and fast). Print: "Codex passes skipped (codex_reviews disabled) — running Claude adversarial only."'
+    : 'Skip this section entirely; do NOT fall back to a Claude subagent — disabled means no extra review step. Print: "Codex review skipped (codex_reviews disabled). Re-enable: `gstack-config set codex_reviews enabled`."';
+  return `\`\`\`bash
+# Codex preflight: one block (functions sourced here don't persist to later blocks).
+_TEL=$(~/.claude/skills/gstack/bin/gstack-config get telemetry 2>/dev/null || echo off)
+_CODEX_CFG=$(~/.claude/skills/gstack/bin/gstack-config get codex_reviews 2>/dev/null || echo enabled)
+source ~/.claude/skills/gstack/bin/gstack-codex-probe 2>/dev/null || true
+if [ "$_CODEX_CFG" = "disabled" ]; then
+  ${m}="disabled"
+elif ! command -v codex >/dev/null 2>&1; then
+  ${m}="not_installed"; _gstack_codex_log_event "codex_cli_missing" 2>/dev/null || true
+elif ! _gstack_codex_auth_probe >/dev/null 2>&1; then
+  ${m}="not_authed"; _gstack_codex_log_event "codex_auth_failed" 2>/dev/null || true
+else
+  ${m}="ready"; _gstack_codex_version_check 2>/dev/null || true
+fi
+echo "CODEX_MODE: $${m}"
+\`\`\`
+
+Branch on the echoed \`CODEX_MODE\`:
+- **\`disabled\`** — the user turned Codex reviews off (\`codex_reviews=disabled\`). ${disabledLine}
+- **\`not_installed\`** — Codex CLI absent. Print: "Codex not installed — using Claude subagent. Install for cross-model coverage: \`npm install -g @openai/codex\`." Fall back to the Claude subagent path.
+- **\`not_authed\`** — installed but no credentials. Print: "Codex installed but not authenticated — using Claude subagent. Run \`codex login\` or set \`$CODEX_API_KEY\`." Fall back to the Claude subagent path.
+- **\`ready\`** — run the Codex pass below.`;
+}