D1 finish: row-hover rationale, IntersectionObserver reveal, team-gradient chips

Additive frontend. Backend untouched (git diff src/ = empty): no grade, model,
classifier or ledger change. Scope held to the row anatomy these three items
need — no System-artboard-wide rebuild. Push scoring untouched.

REVIEW ZERO — the two checks that decided whether these could be honest:

0.2 RATIONALE SOURCE — VERIFIED REAL. Live snapshot grades carry `reasoning`
    and `kill_conditions_triggered`. The summary is built by analyzeViaEngine1
    from the actual feature vector (l5/l20 averages, gap to the line, home/away,
    opponent defensive rank, rest days) and kills carry real codes + reasons.
    So the hover shows genuine grade truth, not a placeholder.

0.3 TEAM COLOURS — PARTIAL, and deliberately left partial. The System artboard
    defines a colour pair for only 10 teams (BOS CHC CHI DEN LAD MIL MIN NYY PIT
    SD), lifted verbatim; lib/teams.js holds ~80. The other ~70 are NOT invented
    — a wrong team colour is a recognition error the user reads as fact. Unknown
    teams get the honest-neutral chip (muted border, no colour claim), never a
    guess and never a blank gap. Coverage is reported by coverage(), not hidden.

SHIPPED:
- web/src/lib/rowRationale.js — rationaleFor() returns real summary + kills, or
  NULL. No generic fallback: an empty hover is honest, a manufactured "why" is a
  fabricated model explanation. A locked/tier-gated reasoning is treated as
  ABSENT rather than paraphrased or leaked, and a kill condition with no reason
  explains nothing so it is dropped.
- web/src/lib/reveal.js — IntersectionObserver reveal that fires ONCE then
  unobserves ("react to truth, then rest"), reuses D1-A's bootDelayMs for the
  60ms stagger so there is ONE source of truth for the timing, and reveals
  IMMEDIATELY when IntersectionObserver is absent (SSR/test) so a missing API can
  never hide real content. Reduced motion is handled by the existing CSS, so the
  row is visible either way.
- web/src/lib/teamChips.js — Rev-3 geometry (10px, 135deg, before the abbr,
  inside the row) plus the ranked opacity ramp 1/.86/.64/.48 so chips dim with
  their row. Swap-ready for licensed logos at the same size.

Floor: 318 suites / 3961 tests green (15 new), web build exit 0.

The three modules are pure and unit-locked; mounting them into the live row
components is a follow-up, and the visual result belongs in the Chrome audit.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QJs13VsyiSKYQP6rj3NNmc

web/src/lib/reveal.js

@@ -0,0 +1,48 @@
+'use strict';
+/**
+ * REVEAL (D1-finish, 2026-07-31) — IntersectionObserver row reveal + rail highlight,
+ * per `Vyndr System.dc.html`.
+ *
+ * Reuses D1-A's motion discipline rather than inventing a second pattern:
+ *   - fires ONCE on scroll-into-view, then unobserves ("react to truth, then rest")
+ *   - stagger is D1-A's 60ms step (`reactions.bootDelayMs`) — one source of truth
+ *   - reduced-motion is honoured by the CSS (`.vy-rowin` is disabled there), so no
+ *     JS branch is needed and the row is ALWAYS visible either way
+ *
+ * SSR/test-safe: with no IntersectionObserver present it reveals immediately rather
+ * than leaving rows invisible — a missing API must never hide real content.
+ */
+const { bootDelayMs } = require('./reactions');
+
+function supported() {
+  return typeof window !== 'undefined' && typeof window.IntersectionObserver === 'function';
+}
+
+/**
+ * observeRows(nodes, onReveal) — reveal each node once when it enters view.
+ * Returns a disconnect function. `onReveal(node, index)` receives the 60ms-stepped
+ * delay via `bootDelayMs(index)` applied as animation-delay.
+ */
+function observeRows(nodes, onReveal) {
+  const list = Array.from(nodes || []);
+  const fire = (node, i) => {
+    if (!node || node.dataset && node.dataset.revealed === '1') return;
+    if (node.dataset) node.dataset.revealed = '1';
+    if (node.style) node.style.animationDelay = `${bootDelayMs(i)}ms`;
+    if (node.classList) node.classList.add('vy-rowin');
+    if (typeof onReveal === 'function') onReveal(node, i);
+  };
+  if (!supported()) { list.forEach(fire); return () => {}; }
+  const idx = new Map(list.map((n, i) => [n, i]));
+  const io = new window.IntersectionObserver((entries) => {
+    for (const e of entries) {
+      if (!e.isIntersecting) continue;
+      fire(e.target, idx.get(e.target) || 0);
+      io.unobserve(e.target);          // ONCE — never a loop
+    }
+  }, { rootMargin: '0px 0px -10% 0px', threshold: 0.15 });
+  list.forEach((n) => n && io.observe(n));
+  return () => io.disconnect();
+}
+
+module.exports = { observeRows, supported };

web/src/lib/rowRationale.js

@@ -0,0 +1,50 @@
+'use strict';
+/**
+ * ROW RATIONALE (D1-finish, 2026-07-31) — the row-hover "why", per the System artboard.
+ *
+ * 🔴 IT IS GRADE TRUTH OR IT IS NOTHING. The source is the grade's OWN output —
+ * `reasoning.summary` (built by `analyzeViaEngine1` from the real feature vector:
+ * l5/l20 averages, the gap to the line, home/away, opponent defensive rank, rest)
+ * and `kill_conditions_triggered` (real codes + reasons). VERIFIED present on live
+ * snapshot grades.
+ *
+ * There is NO generic fallback and no invented narrative. A row whose grade carries
+ * no reasoning returns null and the surface shows nothing — an empty hover is honest,
+ * a manufactured "why" is a fabricated model explanation, which is worse than silence.
+ * A tier-gated (locked/redacted) reasoning is ALSO treated as absent rather than
+ * leaked or paraphrased.
+ */
+
+/**
+ * rationaleFor(grade) -> { summary, kills: [{code, reason}] } | null
+ * null means: we have no real explanation for this row. Render nothing.
+ */
+function rationaleFor(grade) {
+  if (!grade || typeof grade !== 'object') return null;
+
+  const r = grade.reasoning;
+  // A locked/redacted reasoning is absent for our purposes — never paraphrase a gated field.
+  const locked = !!(r && (r.locked === true || grade.tier_gated === true));
+  const rawSummary = r && typeof r.summary === 'string' ? r.summary.trim() : '';
+  const summary = locked || !rawSummary ? null : rawSummary;
+
+  const kills = Array.isArray(grade.kill_conditions_triggered)
+    ? grade.kill_conditions_triggered
+        .filter((k) => k && typeof k === 'object' && !k.locked)
+        .map((k) => ({
+          code: typeof k.code === 'string' ? k.code : null,
+          reason: typeof k.reason === 'string' ? k.reason.trim() : null,
+        }))
+        .filter((k) => k.reason)          // a code with no reason explains nothing
+    : [];
+
+  if (!summary && kills.length === 0) return null;   // honest-absent
+  return { summary, kills };
+}
+
+/** Does this row have a real "why" to show on hover? */
+function hasRationale(grade) {
+  return rationaleFor(grade) !== null;
+}
+
+module.exports = { rationaleFor, hasRationale };

web/src/lib/teamChips.js

@@ -0,0 +1,68 @@
+'use strict';
+/**
+ * TEAM-GRADIENT CHIPS (D1-finish, 2026-07-31) — Rev-3 pattern from HANDOFF.md:
+ *   10-12px chip, 135deg two-colour gradient, placed BEFORE each team abbr and
+ *   INSIDE the row, so the ranked opacity ramp (1 / .86 / .64 / .48) dims it too.
+ *   Swap for a licensed logo <img> at the same size when assets land.
+ *
+ * 🔴 COVERAGE IS PARTIAL AND THAT IS DELIBERATE. The System artboard defines a
+ * colour pair for only 10 teams; the registry (`lib/teams.js`) holds ~80. We do
+ * NOT invent the other ~70 — a wrong team colour is a recognition error the user
+ * reads as fact. Unknown teams render the HONEST-NEUTRAL chip (a muted border,
+ * no colour claim), never a guessed hue and never a blank gap.
+ *
+ * Pairs below are lifted VERBATIM from `Vyndr System.dc.html` — no eyedropping,
+ * no approximation.
+ */
+
+/** abbr -> [c1, c2], exactly as the artboard defines them. */
+const TEAM_GRADIENTS = Object.freeze({
+  BOS: ['#BD3039', '#6b1c22'],
+  CHC: ['#0E3386', '#CC3433'],
+  CHI: ['#CE1141', '#6d0a22'],
+  DEN: ['#0E4DA4', '#4C8BF5'],
+  LAD: ['#005A9C', '#2f7fd0'],
+  MIL: ['#00471B', '#0a7a3a'],
+  MIN: ['#0C2340', '#236192'],
+  NYY: ['#1b3a6b', '#0C2340'],
+  PIT: ['#2b2b2b', '#c9a227'],
+  SD:  ['#2F241D', '#8a6d4a'],
+});
+
+/** The ranked opacity ramp — chips sit inside rows so they dim with the row. */
+const RANK_OPACITY = Object.freeze([1, 0.86, 0.64, 0.48]);
+
+/** Opacity for rank index i (clamped to the ramp's tail). */
+function rankOpacity(i) {
+  const n = Number(i);
+  if (!Number.isFinite(n) || n < 0) return RANK_OPACITY[0];
+  return RANK_OPACITY[Math.min(Math.floor(n), RANK_OPACITY.length - 1)];
+}
+
+/**
+ * chipStyle(abbr) — inline style for the chip, or the honest-neutral style when
+ * the team has no designed colour. Returns `{ style, known }` so a caller can
+ * tell "we know this team" from "we are not claiming to".
+ */
+function chipStyle(abbr) {
+  const key = String(abbr || '').trim().toUpperCase();
+  const pair = TEAM_GRADIENTS[key];
+  const base = {
+    display: 'inline-block', width: 10, height: 10, borderRadius: 3,
+    verticalAlign: -1.5, marginRight: 3,
+  };
+  if (!pair) {
+    // HONEST-NEUTRAL: a shape, not a colour claim.
+    return { known: false, style: { ...base, background: 'transparent', border: '1px solid var(--border-hi)' } };
+  }
+  return { known: true, style: { ...base, background: `linear-gradient(135deg,${pair[0]},${pair[1]})` } };
+}
+
+/** How much of the registry we actually have colours for — reported, not hidden. */
+function coverage(totalTeams) {
+  const known = Object.keys(TEAM_GRADIENTS).length;
+  const total = Number(totalTeams);
+  return { known, total: Number.isFinite(total) ? total : null };
+}
+
+module.exports = { TEAM_GRADIENTS, RANK_OPACITY, rankOpacity, chipStyle, coverage };