Phase 2: predictive model — Elo + Dixon-Coles + Monte Carlo

- buildRatings.ts: walks 49k historical results → World-Football-Elo per team,
  data-calibrated goals model (goals-per-Elo slope, mean goals) + MLE-fit
  Dixon-Coles rho. Top: Spain/Argentina/France (the real 2026 favourites)
- src/lib/model: elo, poisson/dixon-coles, predict, host-advantage, monteCarlo
  (full 48-team sim — group sampling, best-third bipartite allocation, knockout
  advance probs). 20 vitest cases incl. exact per-round count invariants
- Server ModelEngine: live Elo re-rating after each result, per-match W/D/L,
  20k-sim odds, odds-over-time history; broadcast on finished-result changes
- Client: championship board, heat-shaded odds table, lazy-loaded title-race
  chart (Recharts split to its own chunk), match-prediction bars, bracket
  advance overlay
- Verified: odds render, chart populates as injected results re-rate teams live

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

server/src/index.ts

@@ -7,6 +7,7 @@ import fastifyStatic from '@fastify/static';
 import type { WebSocket } from 'ws';
 import { TournamentState } from './tournament';
 import { startLiveLoop } from './liveLoop';
+import { ModelEngine } from './model';
 import type { MatchStatus, ServerMessage } from '../../src/lib/types';
 
 const PORT = Number(process.env.PORT ?? 8787);
@@ -27,20 +28,30 @@ export function buildServer() {
   });
 
   const state = new TournamentState(STATIC_DIR);
+  const model = new ModelEngine(STATIC_DIR);
+  model.recompute(state.allFixtures());
   const clients = new Set<WebSocket>();
 
   const snapshotMessage = (): string =>
     JSON.stringify({ t: 'snapshot', snapshot: state.snapshot() } satisfies ServerMessage);
+  const predictionsMessage = (): string =>
+    JSON.stringify({ t: 'predictions', model: model.current() } satisfies ServerMessage);
 
-  const broadcast = (): void => {
-    const msg = snapshotMessage();
+  const sendAll = (msg: string): void => {
     for (const ws of clients) {
       try { ws.send(msg); } catch { /* closed */ }
     }
   };
 
-  // ---- REST: current snapshot (initial load + a no-WS fallback) ----
+  /** Re-push the snapshot, and predictions too if the finished-result set moved. */
+  const broadcast = (): void => {
+    sendAll(snapshotMessage());
+    if (model.recompute(state.allFixtures())) sendAll(predictionsMessage());
+  };
+
+  // ---- REST: snapshot + predictions (initial load + a no-WS fallback) ----
   app.get('/api/snapshot', async () => state.snapshot());
+  app.get('/api/predictions', async () => model.current());
   app.get('/healthz', async () => ({ ok: true }));
 
   // ---- dev-only: inject a score to exercise the live → standings → WS loop ----
@@ -76,7 +87,7 @@ export function buildServer() {
       }
       if (clients.size >= MAX_WS) { socket.close(1013, 'busy'); return; }
       clients.add(socket);
-      try { socket.send(snapshotMessage()); } catch { /* closed */ }
+      try { socket.send(snapshotMessage()); socket.send(predictionsMessage()); } catch { /* closed */ }
 
       let alive = true;
       socket.on('pong', () => { alive = true; });

server/src/tournament.ts

@@ -63,6 +63,11 @@ export class TournamentState {
     return this.byNum.get(num);
   }
 
+  /** The live fixtures array (for the model engine). */
+  allFixtures(): Fixture[] {
+    return this.fixtures;
+  }
+
   /** True if any match is live or kicks off within `windowMs` of now — used to
    *  poll the APIs often during match windows and rarely when nothing is on. */
   hasLiveActivity(windowMs: number): boolean {