In-play win-probability timeline: the momentum curve on match pages

While a match runs, every poll records the in-play model probability
per game state (insert-if-new on minute+score) into inplay_history.
The match page draws it as a stacked area chart — home fills from the
bottom, away from the top, the gap is the draw — with minute ticks and
a 50% guide. Shows live (under the win-probability bar) and after full
time as its own card. EN/DE strings included.

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

server/src/index.ts

@@ -10,7 +10,8 @@ import { startScheduler } from './ingest/scheduler';
 import { ModelEngine } from './model';
 import { buildPreview, buildTeamProfile } from './preview';
 import { buildScoreboard, snapshotCheck } from './scoreboard';
-import { db, healthAll, oddsFor, latestOddsAll, dbCounts } from './db/db';
+import { db, healthAll, oddsFor, latestOddsAll, dbCounts, inplayHistory, recordInplay } from './db/db';
+import { inPlayProbs } from '../../src/lib/model/inplay';
 import { loadStatic } from './preview';
 import { canonicalTeam } from '../../src/lib/teams';
 import type { MatchStatus, ServerMessage } from '../../src/lib/types';
@@ -56,12 +57,35 @@ export function buildServer() {
     if (model.recompute(state.allFixtures())) sendAll(predictionsMessage());
   };
 
+  // Record the in-play win probability per game state while matches run —
+  // the momentum curve on match pages. Lambdas are the frozen pre-match
+  // expectation (predictions only recompute when the finished set changes).
+  const recordInplayTick = (): void => {
+    const preds = new Map(model.current().matches.map((m) => [m.num, m]));
+    for (const f of state.allFixtures()) {
+      if (f.status !== 'live' || f.homeScore == null || f.awayScore == null) continue;
+      const pred = preds.get(f.num);
+      if (!pred) continue;
+      const minute = f.minute ?? 0;
+      const p = inPlayProbs(pred.lambdaHome, pred.lambdaAway, minute, f.homeScore, f.awayScore);
+      recordInplay(f.num, {
+        minute, home_score: f.homeScore, away_score: f.awayScore,
+        p_home: +p.home.toFixed(4), p_draw: +p.draw.toFixed(4), p_away: +p.away.toFixed(4),
+      });
+    }
+  };
+
   // ---- 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('/api/sources/health', async () => ({ sources: healthAll() }));
   // Bookmaker odds (benchmark for the Model-vs-Market scoreboard; not a model input)
   app.get('/api/odds', async () => ({ odds: latestOddsAll() }));
+  // In-play win-probability history — the momentum curve on match pages.
+  app.get('/api/inplay/:num', async (req) => {
+    const num = Number((req.params as { num: string }).num);
+    return { points: Number.isFinite(num) ? inplayHistory(num) : [] };
+  });
   app.get('/api/scoreboard', async () => buildScoreboard(state));
   // The data lake, quantified — counters for the /data page.
   app.get('/api/data/stats', async () => {
@@ -114,6 +138,7 @@ export function buildServer() {
       );
       if (!f) return reply.code(404).send({ error: 'no such fixture' });
       snapshotCheck(state, model);
+      recordInplayTick();
       broadcast();
       return { ok: true, fixture: f };
     });
@@ -149,6 +174,7 @@ export function buildServer() {
   const stopIngest = startScheduler(state, () => broadcast(), () => {
     const taken = snapshotCheck(state, model);
     if (taken) console.log(`[scoreboard] froze ${taken} pre-kickoff forecast(s)`);
+    try { recordInplayTick(); } catch { /* non-fatal */ }
   });
   app.addHook('onClose', async () => stopIngest());