Merge remote-tracking branch 'origin/main' into dublin-v2

# Conflicts:
#	CHANGELOG.md
#	VERSION
#	agents-digest/gstack-AGENTS.md
#	office-hours/SKILL.md
#	package.json
#	plan-ceo-review/sections/review-sections.md
#	plan-devex-review/sections/review-sections.md
#	plan-eng-review/sections/review-sections.md
#	review/sections/adversarial.md
#	scripts/resolvers/review.ts
#	ship/sections/adversarial.md
#	test/fixtures/golden/factory-ship-SKILL.md
#	test/helpers/carve-guards.ts

document-release/sections/release-body.md

@@ -457,19 +457,27 @@ elif ! command -v codex >/dev/null 2>&1; then
   _CODEX_MODE="not_installed"; _gstack_codex_log_event "codex_cli_missing" 2>/dev/null || true
 elif ! _gstack_codex_auth_probe >/dev/null 2>&1; then
   _CODEX_MODE="not_authed"; _gstack_codex_log_event "codex_auth_failed" 2>/dev/null || true
-elif ! _gstack_codex_model_probe; then
-  _CODEX_MODE="model_unusable"
 else
-  _CODEX_MODE="ready"; _gstack_codex_version_check 2>/dev/null || true
+  # Capture the probe's code: 2 means the CLI cannot execute at all, which is a
+  # different problem (and a different fix) from a model the account can't use.
+  _gstack_codex_model_probe; _CODEX_MP=$?
+  if [ "$_CODEX_MP" -eq 2 ]; then
+    _CODEX_MODE="broken_install"
+  elif [ "$_CODEX_MP" -ne 0 ]; then
+    _CODEX_MODE="model_unusable"
+  else
+    _CODEX_MODE="ready"; _gstack_codex_version_check 2>/dev/null || true
+  fi
 fi
 echo "CODEX_MODE: $_CODEX_MODE"
 ```
 
 Branch on the echoed `CODEX_MODE`:
 - **`disabled`** — the user turned Codex reviews off (`codex_reviews=disabled`). 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`."
-- **`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_installed`** — Codex CLI absent. Print: "Codex not installed — falling back to a Claude subagent (fresh context, but the SAME model family — not an outside model). Install Codex for an actual outside-model read: `npm install -g @openai/codex`." Fall back to the Claude subagent path.
 - **`under_codex`** — this session is already running INSIDE a Codex host, so spawning codex again is the same model reviewing itself at multiplied token cost (#2519). Print exactly one line: "[running under Codex — nested codex passes skipped; set GSTACK_FORCE_CODEX_REVIEW=1 to force]" and skip the codex invocations below; run the section's free in-host pass instead if it defines one.
-- **`not_authed`** — installed but no credentials. Print: "Codex installed but not authenticated — using Claude subagent. Run `codex login` or set `$CODEX_API_KEY`." Fall back to the Claude subagent path.
+- **`not_authed`** — installed but no credentials. Print: "Codex installed but not authenticated — falling back to a Claude subagent (same model family, not an outside model). Run `codex login` or set `$CODEX_API_KEY`." Fall back to the Claude subagent path.
+- **`broken_install`** — the CLI is on PATH but cannot execute (spawn ENOENT, non-executable binary, missing vendor payload). Print: "Codex is installed but its binary cannot run — Codex passes skipped. Reinstall: `npm install -g @openai/codex`." Relay the probe's HINT lines and fall back to the Claude subagent path. This state exists because a missing binary used to land in the model probe's fail-open bucket and report `ready`, so every Codex pass was skipped silently (#2742).
 - **`model_unusable`** — authed but the account cannot use its configured model (#2477: HTTP 400 on every call, usually a stale `model =` pin in `~/.codex/config.toml`). Relay the probe's HINT lines, tell the user the one-line fix (update the pin; `[notice.model_migrations]` names the replacement), and fall back to the Claude subagent path. The ~10s round trip is cached for 1h; timeouts fail open to `ready`.
 - **`ready`** — run the Codex pass below.