P2-9: leaderboard stat labels (SB/ER/TB) + FLAG the grade-degradation root cause

DISPLAY FIX (shipped): the league leaderboard rendered raw snake_case
("stolen_bases U0.5", "earned_runs U2.5"). New canonical short-label lib
web/src/lib/statAbbrev.js (one source, CommonJS + unit-tested) maps stat_type
to SB/ER/TB/HR/K/PTS/… and ExploreHub routes through it. Unknown ids upper-case
their words so raw snake_case can never leak again.

FLAG (reported, NOT silently changed — per the audit's instruction): the "B at
45% confidence" is a BACKEND grading issue, diagnosed against live snapshot:
- 25/25 grades mismatch their own confidence vs grade_thresholds.json (B shown
  at conf 55 = the B- band; a systematic one-sub-tier gap on every prop). The
  surfaced `confidence` is not the probability that derived the letter (likely
  the data-sufficiency penalty applied to display-only).
- 9/25 have projection=0 — the MLB feature path feeds 0 instead of refusing
  (S58 insufficient_data), which also produces the P1-7 broken edge_pct.
Full write-up + do-not list: specs/audit-data/mlb-grade-degradation.md. NOT
re-lettering or shifting thresholds on the frontend — that would hide the bug.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

specs/audit-data/mlb-grade-degradation.md

@@ -0,0 +1,37 @@
+# MLB Grade Pipeline Degradation — Backend Finding (2026-07-17)
+
+Source: phone-audit P1-7 (broken edge board) + P2-9 (B grades at 45% confidence).
+Diagnosed against LIVE `GET /api/snapshot/mlb` on 2026-07-17. This is a BACKEND
+grading/feature-pipeline issue, NOT a frontend display bug. The frontend guards
+(sane-edge cap, statAbbrev) are damage control, not the fix.
+
+## The evidence (25 live MLB grades)
+- **projection == 0 for 9/25.** The model has no projection reference for a third
+  of props — a degraded feature path (the S58 insufficient-data refusal should
+  have caught these; instead they graded with projection 0).
+- **edge_pct on a broken scale.** Distinct values {20, 60, 100, 140}. A real
+  prop-market edge is single-digit %, never past ~40. These are not a market edge
+  (frontend now shows them absent — slateAdapter EDGE_BOARD_SANE_MAX / EdgeCell).
+- **grade <-> confidence mismatch on 25/25.** Every grade's letter disagrees with
+  its own surfaced `confidence` vs `grade_thresholds.json`:
+    - B shown at confidence 55 -> 55 is the B- band (55-59), not B (60-65).
+    - Systematic ~5-point (one sub-tier) gap on every prop.
+  The surfaced `confidence` is NOT the probability that derived the letter.
+
+## Likely root cause (to investigate, not yet fixed)
+1. `confidence` field is post-`apply_data_sufficiency_modifier` (bayesian.py),
+   while the grade letter was assigned from the PRE-penalty prob -> the two
+   disagree by one sub-tier on every prop. Either surface the same value, or
+   re-letter from the penalized confidence. Decide which is the source of truth.
+2. projection==0 for 9/25: the MLB feature/projection path is feeding 0 instead
+   of refusing (S58 `insufficient_data`). Trace `projectionFor` for MLB props;
+   projection 0 also breaks `computeEdge` (=> the 20/60/100/140 garbage).
+
+## Do NOT
+- Do not re-letter or shift thresholds on the frontend (would hide the bug).
+- Do not "fix" edge display by rescaling 140 -> 14 (guessing the scale is its own
+  fabrication). The number must come out of the pipeline correct.
+
+## Frontend already shipped (honest guards)
+- Leaderboard stat labels: `web/src/lib/statAbbrev.js` (raw snake_case -> SB/ER/TB).
+- Edge board: impossible |edge|>40 rendered absent AND excluded from ranking.

tests/unit/statAbbrev.test.js

@@ -0,0 +1,36 @@
+'use strict';
+
+// P2-9 — the canonical SHORT stat label. Raw snake_case ("stolen_bases U0.5")
+// on the leaderboard was the display bug; lock the abbreviations the audit named.
+
+const { statAbbrev, STAT_ABBREV } = require('../../web/src/lib/statAbbrev');
+
+describe('statAbbrev', () => {
+  test('the audit-named MLB stats map to short labels', () => {
+    expect(statAbbrev('stolen_bases')).toBe('SB');
+    expect(statAbbrev('earned_runs')).toBe('ER');
+    expect(statAbbrev('total_bases')).toBe('TB');
+    expect(statAbbrev('home_runs')).toBe('HR');
+    expect(statAbbrev('strikeouts')).toBe('K');
+  });
+
+  test('NBA stats too', () => {
+    expect(statAbbrev('points')).toBe('PTS');
+    expect(statAbbrev('rebounds')).toBe('REB');
+    expect(statAbbrev('assists')).toBe('AST');
+  });
+
+  test('an unknown id upper-cases its words (never leaks raw snake_case)', () => {
+    expect(statAbbrev('some_new_stat')).toBe('SOME NEW STAT');
+    expect(statAbbrev('some_new_stat')).not.toContain('_');
+  });
+
+  test('null / empty is safe', () => {
+    expect(statAbbrev(null)).toBe('');
+    expect(statAbbrev('')).toBe('');
+  });
+
+  test('no label contains an underscore (all are real abbreviations)', () => {
+    for (const v of Object.values(STAT_ABBREV)) expect(v).not.toContain('_');
+  });
+});

web/src/components/ExploreHub.tsx

@@ -5,6 +5,7 @@ import SportBadge from '@/components/vyndr/SportBadge';
 import GradeBadge from '@/components/vyndr/GradeBadge';
 import { playerHref } from '@/lib/playerHref';
 import { dedupeLeaders } from '@/lib/playerGrouping';
+import { statAbbrev } from '@/lib/statAbbrev';
 
 /**
  * ExploreHub (Session 42 leaders; Session 60 night2/C — THE AGGREGATOR).
@@ -147,7 +148,7 @@ export default function ExploreHub() {
               <span style={{ fontWeight: 700, fontSize: 13, color: '#fff', whiteSpace: 'nowrap' }}>{r.player}</span>
               {r.team && <span className="mono" style={{ fontSize: 10, color: 'var(--text-1)' }}>{r.team}</span>}
             </div>
-            <div className="mono" style={{ textAlign: 'right', fontSize: 12, color: '#C8CCD6' }}>{r.stat} {r.side}{r.line}</div>
+            <div className="mono" style={{ textAlign: 'right', fontSize: 12, color: '#C8CCD6' }}>{statAbbrev(r.stat)} {r.side}{r.line}</div>
             <div className="mono" style={{ textAlign: 'right', fontSize: 13, fontWeight: 600, color: 'var(--text-0)' }}>{r.confidence != null ? `${r.confidence}%` : '—'}</div>
             <div style={{ display: 'flex', justifyContent: 'center' }}><GradeBadge grade={r.grade} size="sm" /></div>
           </a>

web/src/lib/statAbbrev.js

@@ -0,0 +1,35 @@
+/**
+ * statAbbrev — the ONE canonical SHORT stat label ("total_bases" -> "TB").
+ *
+ * The compact, mono, grid-aligned surfaces (leaderboard, breadth, top signals)
+ * want abbreviations, not the long "Total Bases" form gradeAdapter.statLabel
+ * emits for the roomy grade card. Raw snake_case ("stolen_bases U0.5") is a
+ * display bug — every ranked/gridded surface routes stat_type through here.
+ *
+ * CommonJS so it's importable by .tsx (allowJs) AND unit-testable by Jest.
+ */
+
+'use strict';
+
+const STAT_ABBREV = {
+  // MLB — batting
+  total_bases: 'TB', home_runs: 'HR', hits: 'H', rbi: 'RBI', runs: 'R',
+  stolen_bases: 'SB', doubles: '2B', triples: '3B', walks: 'BB', singles: '1B',
+  // MLB — pitching
+  strikeouts: 'K', hits_allowed: 'HA', earned_runs: 'ER', innings_pitched: 'IP',
+  outs: 'OUTS', walks_allowed: 'BB',
+  // NBA / WNBA
+  points: 'PTS', rebounds: 'REB', assists: 'AST', threes: '3PT', steals: 'STL',
+  blocks: 'BLK', pra: 'PRA', turnovers: 'TO', pr: 'PR', pa: 'PA', ra: 'RA',
+  // NHL / soccer (best-effort)
+  shots_on_goal: 'SOG', saves: 'SV', goals: 'G', shots: 'SH',
+};
+
+/** Short display label for a stat_type id; unknown ids upper-case the words. */
+function statAbbrev(stat) {
+  if (!stat) return '';
+  if (STAT_ABBREV[stat]) return STAT_ABBREV[stat];
+  return String(stat).replace(/_/g, ' ').toUpperCase();
+}
+
+module.exports = { STAT_ABBREV, statAbbrev };