Recency-weighted v4 model: fast-Elo blend, Team-DC majority, nightly refit

Validated on the strict 2018-2022 window and confirmed on the untouched
2022-2026 test set (RPS 0.1703 vs 0.1721 over 4,448 matches):
- the Elo member now blends 30% of a 3x-faster Elo walk, so recent
  results move ratings much harder
- ensemble weight shifts from 75/25 toward Elo to 45/55 toward the
  time-decayed Team-DC member — the recent-form model now leads
- Team-DC refits nightly (and at boot) on the 15-year window plus every
  finished 2026 match, via a new committed-at-build dcTrain.json
  (server-only, excluded from the PWA precache)
- a recent-form goal multiplier was also tested and did NOT validate;
  it ships disabled, and backtest.json records the whole decision

buildBacktest.ts grew the experiment harness: wider xi/k grids, the
fast-Elo and form variants, a pre-registered ship bar (>=0.0005
validation RPS), and a 7-day refit-cadence check. Older ratings.json
files still work — all new model fields are optional with golden
regression coverage.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

server/src/index.ts

@@ -35,6 +35,7 @@ export function buildServer() {
   db(); // open + migrate SQLite before anything reads it
   const state = new TournamentState(STATIC_DIR);
   const model = new ModelEngine(STATIC_DIR);
+  model.refitTeamDc(state.allFixtures()); // current Team-DC from day one (covers restarts mid-tournament)
   model.recompute(state.allFixtures());
   const clients = new Set<WebSocket>();
 
@@ -151,6 +152,12 @@ export function buildServer() {
   });
   app.addHook('onClose', async () => stopIngest());
 
+  // ---- nightly Team-DC refit (backtest-validated): learn from this tournament ----
+  const refitTimer = setInterval(() => {
+    if (model.refitTeamDc(state.allFixtures())) broadcast();
+  }, 24 * 60 * 60 * 1000);
+  app.addHook('onClose', async () => clearInterval(refitTimer));
+
   // ---- static SPA (prod) with history fallback ----
   if (existsSync(STATIC_DIR)) {
     void app.register(fastifyStatic, { root: STATIC_DIR, wildcard: false });