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

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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>
This commit is contained in:
Kev
2026-07-17 01:42:03 -04:00
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commit 77e8937a56
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specs/audit-data/mlb-grade-degradation.md
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# 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.