phase: 02_level_content_and_validation

Phase `02_level_content_and_validation` — final verification **green**.

- **Gate:** `bash .agents/validate.sh` → ruff ✅ · pyright 0 errors ✅ · `undercooked-levels validate` OK (2 levels) ✅ · **668 passed** (incl. 10 Playwright e2e) ✅ · coverage **100%** ✅ · repo hygiene ✅
- **Criteria:** `validate` exit 0, one line per level; `list` = `01_first_kitchen`, `02_double_shift` in campaign order; live `:8000` `/healthz` 200, `/api/levels` (+detail) carries both levels with numeric `target_score`/`time_limit` and no grid/station leakage, `/api/config` correct, unknown id → 404, startup log `content loaded: 2 level(s), 4 recipe(s)`; `validate --dir tests/fixtures/levels/_bad/` → exit 1 with named `RECIPE_STATION_MISSING` / `SERVE_REACHABLE` / `TARGET_IMPLAUSIBLE`; A8 lock test proves a YAML-only level reaches loader+API+CLI.
- **Defect fixed (pre-existing path, phase-02-triggered):** `undercooked` with unusable content printed the report then a raw traceback and exited `1`. `src/undercooked/__main__.py` now catches `ContentError` → one closing line, exit `2` (like a bad setting); 2 new tests in `tests/unit/test_main.py` (incl. non-content failures still propagate).
- **Docs pass (full, project-wide):** README (content gate + exit `2`, config section), AGENTS.md §3, `docs/LEVELS.md` (startup refusal + exact CLI exit codes), `docs/DEPLOYMENT.md` (crash-loop diagnosis bullet); DESIGN/TESTING re-read, consistent.
- **Container re-verified (no phase-01 regression):** `podman build -f Containerfile` succeeds; the image ships `levels/` and serves `/healthz` 200, `/api/levels` (2 levels), `/` 200 as non-root.
- **Deviation to note:** the phase overview names `tests/fixtures/levels/bad/`; the actual broken-fixture dir is `tests/fixtures/levels/_bad/` (the `_` prefix is what keeps it out of normal discovery). Overview files are read-only to me — README/LEVELS.md document the real path.
- No git index/history commands run; all changes left unstaged for the harness. ntfy notification sent.

tests/fixtures/levels/recipes.yaml

@@ -0,0 +1,18 @@
+# tests/fixtures/levels/recipes.yaml — the minimal book for the test-isolated
+# levels directory (see tests/conftest.py `isolated_levels_dir`).
+#
+# A campaign with zero levels is legal (docs/LEVELS.md), but every
+# `create_app()` still needs a recipe book to load. Tests that want actual
+# levels build their own under `tmp_path`; the shipped campaign lives in
+# `levels/` and is covered by tests/unit/test_shipped_content.py.
+ingredients: [tomato]
+recipes:
+  tomato_soup:
+    id: tomato_soup
+    name: Test Soup
+    base_score: 10
+    ingredients:
+      - {kind: tomato, form: raw}
+    steps:
+      - {kind: pick, station: spawn_shelf}
+      - {kind: serve, station: serve}