# frontend/ — agent instructions

The **SSR + static-asset service**: server-rendered crawlable pages, the
interactive tool's SPA shells, and every static asset. No climate data, no DB,
no compute — everything comes from `backend/`'s content API over HTTP.

Read the root `CLAUDE.md` first for the branch model, deploy contract and image
names.

## The live service is Go — `server/`

`server/` (module `thermograph/frontend`, Go 1.26) is what builds, tests, ships
and runs. It is the only thing in the `emi/thermograph/frontend` image.

The Python files at this level — `app.py`, `content.py`, `api_client.py`,
`format.py`, `content_loader.py`, `paths.py`, `templates/*.html.j2` — are the
**superseded original implementation**, kept as the reference the port was made
from. Nothing deploys them. Don't add features there; don't take their file
paths as current. (They still carry duplicate copies of some contracts below —
notably `api_client.py`'s `API_VERSION` pin and `format.py`'s `F_COUNTRIES`. If
you use them locally, keep them in step or you will debug a phantom.)

Deleting them is a live question, not a settled one — the Python test tiers
still run against the fixtures the Go tests share. Raise it rather than doing it
in passing.

## Build & verify

- `cd server && go build ./... && go vet ./... && go test ./...` — **the suite
  that matters.**
- **CI runs it inside `Dockerfile`'s builder stage**, which does `gofmt -l` +
  `go vet` + `go test ./...` before compiling. A failing Go test therefore fails
  the image build — that is the whole frontend check. There is no separate
  frontend test step in any workflow.
- `make test-unit` / `make test-integration` — the **Python** tiers. Local only;
  CI runs neither. The unit tier is hermetic (SSR rendering fed committed
  fixtures); the integration tier pulls and runs a real backend image.
- `make backend-up` / `make backend-down` — a local backend container for dev.
  The image tag is derived from this checkout (last commit touching `backend/`,
  the same domain-keyed rule build-push and deploy use); override with
  `THERMOGRAPH_BACKEND_TEST_TAG=sha-<12hex>`.
- `make capture-fixtures` — refresh `tests/fixtures/*.json` from a live backend.
  **These fixtures feed the Go tests too**, not just the Python ones.

## Running it

`THERMOGRAPH_API_BASE_INTERNAL` is **required** — the boot fails loudly without
it, as the Python raised at import.

Build in `server/`, run from `frontend/`: `static/` and `content/` resolve
relative to the working directory, while templates are embedded in the binary.

```bash
cd server && go build -o thermograph-frontend .
cd ..
THERMOGRAPH_API_BASE_INTERNAL=http://127.0.0.1:8137 THERMOGRAPH_BASE=/thermograph \
  ./server/thermograph-frontend
```

Other env: `THERMOGRAPH_BASE` (default `/thermograph`; the Dockerfile sets `/`),
`THERMOGRAPH_API_VERSION` (default `v2`), `THERMOGRAPH_API_BASE_PUBLIC`
(browser-facing backend origin when cross-origin; empty = same-origin, today's
default), `THERMOGRAPH_SSR_CACHE_TTL` (default 600s),
`THERMOGRAPH_GOOGLE_VERIFY` / `THERMOGRAPH_BING_VERIFY`, `PORT` (default 8080).

Boot is fail-loud on bad **config or content**: a missing backend URL, a garbage
TTL, or malformed `content/*.yaml` all stop the process rather than 500 on the
first request.

## Layout

- **`server/internal/content/`** — the SSR page handlers (climate hub, city,
  month, records, glossary, about, privacy) + `robots.txt` + `sitemap.xml`,
  plus the template funcmap and SEO helpers. The backend's
  `content_payloads.py` owns `page_title` / `canonical_path` / `breadcrumb` /
  `jsonld`, **not this domain**.
- **`server/internal/contentapi/`** — the backend `/content/*` client: TTL
  cache, bounded LRU, per-key single-flight, origin forwarding. All four
  properties are load-bearing; read the file before changing caching.
- **`server/internal/render/`** + `render/templates/*.tmpl` — `html/template`
  over an `embed.FS`, plus the ETag helpers. Templates are **embedded**, so a
  template change needs a rebuild.
- **`server/internal/{config,format,contentdata,handlers}/`** — env parsing,
  unit-aware °C/°F formatting and band names, the glossary/pages loader, and
  the SPA-shell + static handlers.
- **`static/*.js`** — `app.js` (map/search/results + inline SVG chart),
  `calendar.js`/`day.js`/`score.js`/`compare.js` (SPA shells), `account.js`
  (auth), `cache.js` (IndexedDB cache + `/cell` bundle prefetch), `shared.js`.
- **`static/style.css`** — the single hand-written stylesheet; design tokens live
  here, documented in `DESIGN.md`.
- **`content/*.yaml`** — structured SSR copy, loaded by
  `server/internal/contentdata`.

## Contracts with the backend

- **API version is pinned in exactly two places** — `server/internal/config`'s
  `THERMOGRAPH_API_VERSION` (Go) and `static/account.js`'s exported
  `API_VERSION` plus the `uv(path)` helper (JS). Never hardcode `api/v2/...`
  anywhere else. Bump both in one PR, and only after the target backend's
  `/api/version` confirms it serves that version and its `min_frontend` doesn't
  exclude the one you're leaving.
- **`shared.js::pctOrd()` must mirror `backend`'s `data/grading.py::pct_ordinal()`**
  in behaviour — floor into `1..99`, never 0 or 100 — and so must
  `server/internal/format`'s `PctOrdinal`. Every percentile on every surface
  goes through one of the three; if they diverge, the same reading says two
  different things in two places.
- **`/cell` bundle + ETag** — `cache.js` fetches `/api/v2/cell` once per view-set
  and slices it, revalidating with `If-None-Match`. The slice→view map must track
  the backend's payload shape.
- **Fahrenheit country set** — `server/internal/format`'s `FCountries` and
  `static/units.js`'s `F_REGIONS` must stay identical to the backend's
  `F_COUNTRIES`. Both are now asserted by tests in
  `server/internal/format/format_test.go`: the backend cross-check is a
  checkout-only guard (the image build context is `frontend/`, so `backend/` is
  unreachable there), while the `units.js` check runs in the image build too —
  `Dockerfile` copies that one file into the builder stage for exactly that
  reason.
- **Boot must survive an unreachable backend.** The IndexNow-key fetch is tried
  once at boot, caught, and falls back to a lazy per-request lookup.
  Asynchronous FE/BE deploys depend on this — don't make it fatal.

## Commits & PRs

Concise and technical. Never mention AI, assistants or automated authorship.
