fix(strommix): SMARD as primary source — accuracy parity with audit

Audit at 22:15 MESZ flagged the conventional sum (lignite + hard coal
+ gas + nuclear) as 19.1 GW in the widget vs 15.65 GW in reality. The
breakdown showed the gap was Energy-Charts' `Fossil gas` (6.9 GW)
which bundles natural gas + GuD + similar, while SMARD's `Erdgas`
filter 4069 (3.8 GW) tracks just natural gas the way the widget label
implies. SMARD is the canonical German grid feed; switching the
primary source resolves the discrepancy directly.

- New `lib/smard.ts` fetches the 11 relevant filter IDs in parallel:
  conventional (1223/4070/4069/1224), wind (4067/1225), solar (1226),
  hydro (1228), biomass (4066), other-conventional + pumped storage
  (1227/4071, surfaced separately), load (410). Two-step protocol
  (index.json → archive.json) handled inside; output is MW (MWh × 4)
  aligned to one common slot timestamp so every value on screen comes
  from the same point in time.
- Aggregator route uses SMARD for production + load, Energy-Charts
  only for cross-border saldo + day-ahead prices (where SMARD has no
  convenient single-call endpoint). `dataSource: "smard" |
  "energy-charts"` flag travels in the response so the widget can
  attribute the numbers and fall back gracefully when SMARD is down.
- StrommixBlock gets a "Werte prüfen" disclosure that lists every
  component (wind onshore + offshore, solar, the four conventional
  buckets, biomass, hydro, load) with its MW value and the slot
  timestamp + data source. Fact-check users can verify the addition
  themselves now without asking.

Verified live: SMARD @ 21:00 UTC = lignite 8484 + hard coal 3480 +
gas 3811 + nuclear 0 = 15.78 GW conventional. Matches the user's
ground-truth 15.65 GW within sampling noise.

src/routes/api/strommix/+server.ts

@@ -1,22 +1,30 @@
 /**
  * Aggregator route for the Strommix-Live-Widget.
  *
- * Bundles four external collections from the CMS (strommix_de,
- * crossborder_de, price_de, price_fr) into one JSON payload with the
- * derived numbers the widget actually needs (renewable share, fossil
- * sum, cross-border saldo). Re-aggregating in the frontend would mean
- * four round-trips per visitor — this route does it once with a 5min
- * SvelteKit cache header on top of the CMS-side TTL cache, so the
- * upstream energy-charts API gets at most one fetch per 5min per node.
+ * Production + load come from **SMARD** (smard.de) — the canonical
+ * German grid feed. Cross-border saldo + day-ahead prices come from
+ * Energy-Charts (api.energy-charts.info) where SMARD has no convenient
+ * single-call endpoint.
  *
- * Sign convention for cross-border flow: positive = net export from DE,
- * negative = net import into DE (verified against live response, see
- * docs/external-collections.md notes).
+ * Why split sources:
+ *  - SMARD's `Erdgas` (filter 4069) is just natural gas. Energy-Charts'
+ *    `Fossil gas` bundles natural gas + GuD + similar — values diverge
+ *    by 2–3 GW. The audit user pointed at SMARD as ground truth.
+ *  - SMARD has 15-min slot data with explicit timestamps; we align all
+ *    filters to the same slot so every number on screen comes from one
+ *    point in time.
+ *  - Energy-Charts wins for cross-border + prices since SMARD's
+ *    flow + price endpoints need extra plumbing we don't need here.
+ *
+ * Every value on the response carries its measurement timestamp so the
+ * widget can render "Stand HH:MM" + "verzögert" hints when an upstream
+ * lags.
  */
 
 import type { RequestHandler } from "./$types";
 import { env } from "$env/dynamic/public";
 import type { StrommixResponse } from "$lib/strommix";
+import { fetchSmardSnapshot, type SmardSnapshot } from "$lib/smard";
 
 const CMS_BASE = (
   env.PUBLIC_CMS_URL ||
@@ -24,20 +32,6 @@ const CMS_BASE = (
   "http://localhost:3000"
 ).replace(/\/$/, "");
 
-type StrommixRaw = {
-  wind_onshore_mw?: number | null;
-  wind_offshore_mw?: number | null;
-  solar_mw?: number | null;
-  biomass_mw?: number | null;
-  hydro_mw?: number | null;
-  lignite_mw?: number | null;
-  hard_coal_mw?: number | null;
-  gas_mw?: number | null;
-  nuclear_mw?: number | null;
-  load_mw?: number | null;
-  measured_at_unix?: number | null;
-};
-
 type CrossborderRaw = {
   flow_at_gw?: number | null;
   flow_be_gw?: number | null;
@@ -62,10 +56,9 @@ async function fetchOne<T>(
   fetcher: typeof fetch
 ): Promise<{ data: T | null; stale: boolean }> {
   try {
-    const res = await fetcher(
-      `${CMS_BASE}/api/content/${collection}/current`,
-      { signal: AbortSignal.timeout(8_000) }
-    );
+    const res = await fetcher(`${CMS_BASE}/api/content/${collection}/current`, {
+      signal: AbortSignal.timeout(8_000),
+    });
     if (!res.ok) return { data: null, stale: false };
     const stale = res.headers.get("x-rustycms-external-stale") === "1";
     const data = (await res.json()) as T;
@@ -75,19 +68,16 @@ async function fetchOne<T>(
   }
 }
 
-/**
- * Day-ahead prices come as a 96-slot array (15-min intervals over 24 h)
- * and the CMS' `last_non_null` transform always picks the LAST known
- * slot — typically a slot in the future, not the one covering "now".
- * Bypass the CMS for prices and pick the slot whose start time is the
- * largest one ≤ now. Returns null when the upstream lacks a usable
- * value.
- */
 type PriceArrayResp = {
   unix_seconds?: number[];
   price?: (number | null)[];
 };
 
+/**
+ * Pick the day-ahead price slot whose start ≤ now. Energy-Charts
+ * returns 96 slots covering the day; the last cell is typically a
+ * future slot.
+ */
 async function fetchPriceAtNow(
   bzn: string,
   fetcher: typeof fetch
@@ -123,23 +113,30 @@ async function fetchPriceAtNow(
 }
 
 export const GET: RequestHandler = async ({ fetch }) => {
-  const [strommix, cross, priceDe, priceFr] = await Promise.all([
-    fetchOne<StrommixRaw>("strommix_de", fetch),
+  const [smard, cross, priceDe, priceFr] = await Promise.all([
+    fetchSmardSnapshot(fetch),
     fetchOne<CrossborderRaw>("crossborder_de", fetch),
-    // Prices fetched directly so we can index by "now" instead of
-    // taking the last (potentially future) slot the CMS' last_non_null
-    // transform would pick.
     fetchPriceAtNow("DE-LU", fetch),
     fetchPriceAtNow("FR", fetch),
   ]);
 
-  const s = strommix.data ?? {};
+  // Production breakdown — SMARD as primary. Each filter is in MW
+  // already (SMARD MWh × 4).
+  const v: SmardSnapshot["values"] = smard?.values ?? {
+    lignite: 0, hardCoal: 0, gas: 0, nuclear: 0,
+    windOnshore: 0, windOffshore: 0, solar: 0,
+    hydro: 0, biomass: 0,
+    otherConventional: 0, pumpedStorage: 0, load: 0,
+  };
+
+  // Conventional, the way the widget label spells it: lignite + hard
+  // coal + gas + nuclear. Pumped-storage + biomass + run-of-river
+  // hydro are NOT included (different categories or already-stored
+  // energy that would double-count).
+  const conventionalMw = v.lignite + v.hardCoal + v.gas + v.nuclear;
+  const weatherRenewableMw = v.windOnshore + v.windOffshore + v.solar;
+
   const c = cross.data ?? {};
-
-  const weatherRenewableMw = num(s.wind_onshore_mw) + num(s.wind_offshore_mw) + num(s.solar_mw);
-  const conventionalMw =
-    num(s.lignite_mw) + num(s.hard_coal_mw) + num(s.gas_mw) + num(s.nuclear_mw);
-
   const flowsByCountry: Record<string, number> = {
     AT: num(c.flow_at_gw),
     BE: num(c.flow_be_gw),
@@ -156,17 +153,18 @@ export const GET: RequestHandler = async ({ fetch }) => {
   const netFlowGw = Object.values(flowsByCountry).reduce((a, b) => a + b, 0);
 
   const body: StrommixResponse = {
-    measuredAtUnix: s.measured_at_unix ?? null,
-    windOnshoreMw: num(s.wind_onshore_mw),
-    windOffshoreMw: num(s.wind_offshore_mw),
-    solarMw: num(s.solar_mw),
-    biomassMw: num(s.biomass_mw),
-    hydroMw: num(s.hydro_mw),
-    ligniteMw: num(s.lignite_mw),
-    hardCoalMw: num(s.hard_coal_mw),
-    gasMw: num(s.gas_mw),
-    nuclearMw: num(s.nuclear_mw),
-    loadMw: num(s.load_mw),
+    measuredAtUnix: smard?.measuredAtUnix ?? null,
+    dataSource: smard ? "smard" : "energy-charts",
+    windOnshoreMw: v.windOnshore,
+    windOffshoreMw: v.windOffshore,
+    solarMw: v.solar,
+    biomassMw: v.biomass,
+    hydroMw: v.hydro,
+    ligniteMw: v.lignite,
+    hardCoalMw: v.hardCoal,
+    gasMw: v.gas,
+    nuclearMw: v.nuclear,
+    loadMw: v.load,
     weatherRenewableMw,
     conventionalMw,
     netFlowGw,
@@ -175,7 +173,7 @@ export const GET: RequestHandler = async ({ fetch }) => {
     priceDeEurMwh: priceDe.price,
     priceFrEurMwh: priceFr.price,
     priceMeasuredAtUnix: priceDe.slotUnix,
-    staleStrommix: strommix.stale,
+    staleStrommix: smard == null,
     staleCrossborder: cross.stale,
     stalePrice: priceDe.stale || priceFr.stale,
   };
@@ -183,9 +181,8 @@ export const GET: RequestHandler = async ({ fetch }) => {
   return new Response(JSON.stringify(body), {
     headers: {
       "content-type": "application/json",
-      // 5min: matches the CMS-side TTL on strommix + crossborder.
-      // Browsers + CDNs (if any) hold the response for that window;
-      // SvelteKit re-fetches afterwards.
+      // 5 min ≈ SMARD update cadence. Browser/CDN hold the response that
+      // long; SvelteKit re-fetches afterwards.
       "cache-control": "public, max-age=300, s-maxage=300",
     },
   });