Session 38: Design system Phase G — living layer, i18n/odds, a11y, paywall, parlay math (1890 tests)

VYNDR 2.0 conversion, Phase G (the systems that make the design alive). All 5 wired. Frontend-only; zero backend changes. - lib/parlayMath.js: correlation model (0.62/0.34/0.06/0) + parlayGrade penalty + grade->odds + combined odds (frontend; backend parlayService unchanged). - lib/oddsFormat.js: fmtOdds across american/decimal/fractional/implied with the totals-pass-through rule (safer than the prototype's parseAm, which would mis-convert 228.5) + region presets. - lib/prefs.js: applyPrefs sets <html data-*> (the S33 a11y CSS layer) + load/save. - lib/liveTick.js: single tick engine (SSR/test-safe, no auto-start, fresh state). - lib/checkout.js: checkoutUrl(plan). - LiveLayer (useLive/LiveNumber/HeartbeatBar) under the Nav ticker; GlobalHosts in layout applies prefs + registers __prefs/__goPaywall/__checkout + hosts the Preferences and Paywall modals. Nav read-meter is now a paywall trigger. Gotchas: useEffect can't return a Set.delete unsub directly (boolean != cleanup); header grew to 124px so layout paddingTop + Slate sticky-top updated to match. 18 new tests. Backend 1872 -> 1890, 146 suites, zero regressions. Web build clean. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
2026-06-16 10:37:31 -04:00
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+/* ============================================================
+   VYNDR 2.0 — parlay correlation math (§12).
+   Ported from the prototype's vyndr-parlay.jsx. Plain CommonJS so the
+   Parlay Lab imports it (allowJs) AND Jest exercises it directly.
+
+   NOTE: the BACKEND parlayService (Session 28) owns server-side combined
+   odds + suggestions. This module is the FRONTEND correlation model that
+   powers the Parlay Lab's live matrix + grade penalty.
+   ============================================================ */
+
+// Grade → representative American odds (the prototype's GRADE_ODDS).
+const GRADE_ODDS = { 'A+': -135, A: 110, 'A-': 115, 'B+': 125, B: 135, 'B-': 150, C: 175, D: 240 };
+
+function amToDec(am) {
+  return am > 0 ? am / 100 + 1 : 100 / -am + 1;
+}
+function decToAm(dec) {
+  return dec >= 2 ? Math.round((dec - 1) * 100) : Math.round(-100 / (dec - 1));
+}
+function fmtAmerican(am) {
+  return (am > 0 ? '+' : '') + am;
+}
+
+/**
+ * Pairwise correlation (§12): same player legs move together hardest,
+ * then same team, then same league, then ~independent across sports.
+ */
+function getCorrelation(legA, legB) {
+  if (!legA || !legB) return 0;
+  if (legA.player && legA.player === legB.player) return 0.62;
+  if (legA.team && legA.team === legB.team && legA.sport === legB.sport) return 0.34;
+  if (legA.sport && legA.sport === legB.sport) return 0.06;
+  return 0;
+}
+
+/** Highest pairwise correlation across the slip (the worst hidden drag). */
+function maxCorrelation(legs) {
+  let max = 0;
+  for (let i = 0; i < legs.length; i++) {
+    for (let j = i + 1; j < legs.length; j++) {
+      max = Math.max(max, getCorrelation(legs[i], legs[j]));
+    }
+  }
+  return max;
+}
+
+/** All correlated pairs as [i, j, correlation]. */
+function correlationPairs(legs) {
+  const pairs = [];
+  for (let i = 0; i < legs.length; i++) {
+    for (let j = i + 1; j < legs.length; j++) {
+      pairs.push([i, j, getCorrelation(legs[i], legs[j])]);
+    }
+  }
+  return pairs;
+}
+
+const GRADE_ORDER = ['A+', 'A', 'B+', 'B', 'C', 'D'];
+
+/**
+ * Combined parlay grade. Averages the leg grades, then bumps the slip DOWN
+ * one tier when any pair is strongly correlated (>0.4) — correlated stacks
+ * are riskier than the books' independent pricing implies.
+ */
+function parlayGrade(legs) {
+  if (!legs || !legs.length) return '—';
+  const avg = legs.reduce((s, l) => s + Math.max(0, GRADE_ORDER.indexOf(String(l.grade || 'B').replace('-', ''))), 0) / legs.length;
+  const penalty = maxCorrelation(legs) > 0.4 ? 1 : 0;
+  const idx = Math.min(GRADE_ORDER.length - 1, Math.round(avg + penalty));
+  return GRADE_ORDER[idx];
+}
+
+/** Combined decimal odds (product of per-leg decimal odds). */
+function combinedDecimal(legs) {
+  return legs.reduce((d, l) => d * amToDec(GRADE_ODDS[l.grade] != null ? GRADE_ODDS[l.grade] : 110), 1);
+}
+
+/** Combined odds as an American string, or "—" for an empty slip. */
+function combinedAmerican(legs) {
+  if (!legs || !legs.length) return '—';
+  return fmtAmerican(decToAm(combinedDecimal(legs)));
+}
+
+module.exports = {
+  GRADE_ODDS,
+  GRADE_ORDER,
+  amToDec,
+  decToAm,
+  fmtAmerican,
+  getCorrelation,
+  maxCorrelation,
+  correlationPairs,
+  parlayGrade,
+  combinedDecimal,
+  combinedAmerican,
+};