backend/CLAUDE.md

@@ -38,13 +38,20 @@ for systemd/CI callers. Entry target is `app:app`.
   `cache.js` reads `null` cross-origin and never revalidates. Don't change the
   ETag derivation or that list without checking `frontend/static/cache.js`.
 - **`data/grading.py::pct_ordinal()`** is mirrored by `frontend`'s
-  `shared.js::pctOrd()` — floor a percentile into `1..99`, never 0 or 100.
+  `server/internal/format::PctOrdinal` (SSR) and `static/shared.js::pctOrd()`
+  (browser) — floor a percentile into `1..99`, never 0 or 100.
   `TEMP_BANDS`/`RAIN_BANDS` are the source of truth for tier names and
   thresholds; changing them without the frontend produces tiers drawn in colours
   that disagree with the labels the API returns.
-- **Fahrenheit country set** — `api/content_payloads.py`'s `F_COUNTRIES` must stay
-  identical to `frontend`'s `format.py::F_COUNTRIES` and `static/units.js`'s
-  `F_REGIONS`. There is a test asserting this.
+- **Fahrenheit country set** — `api/content_payloads.py`'s `F_COUNTRIES` is
+  canonical; `frontend`'s `server/internal/format::FCountries` and
+  `static/units.js`'s `F_REGIONS` must stay identical to it. Both are asserted
+  by tests in `frontend/server/internal/format/format_test.go` — but note the
+  backend cross-check **skips in CI** (the frontend image's build context is
+  `frontend/`, so this file is unreachable from the builder stage, which is the
+  only place CI runs those tests). It fires on a full checkout. The `units.js`
+  check does run in the image build. `frontend/format.py`'s copy is the
+  superseded Python service's and is not deployed.
 - **`/healthz` and `/api/version` are deliberately I/O-free** so they stay cheap
   under tight healthcheck intervals.