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 };