# MLB Grade Pipeline Degradation — FIXED (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. Backend grading
bug, fixed at the source in the generic grade path (`engine1` +
`analyzeViaEngine1`), which grades EVERY sport.

## Before (25 live MLB grades, degraded)
- **projection == 0 for 9/25** — graded on a zero projection.
- **edge_pct quantized to {20, 60, 100, 140}** — the 100s were the proj=0
  degeneracy `(line - 0)/line = 100%`.
- **grade ↔ confidence mismatch** — 10/25 disagreed even at the 4-letter level
  (25/25 vs the stricter 11-step bands).

## Root causes + fixes (commit `888d103`)
1. **projection=0 bypassed the refusal gate.** `projectionFor` returned
   `l5_avg` even when 0 (finite → the `== null` gate passed it). FIX: a
   non-positive reference is not a projection — `projectionFor` skips it and
   falls through to the next POSITIVE reference (l5 → l20 → per_90 → xg); when
   none is positive it returns null and the read REFUSES (`insufficient_data`).
   The gate also gained an explicit `> 0` guard — the invariant is structural.
2. **edge_pct.** Formula was already `(model - line)/line` (the intended
   semantics); the {100} cluster was purely the proj=0 degeneracy. With fix 1
   those refuse. Main-line edge now reuses the VALIDATED projection so edge and
   the persisted `projection` can't diverge.
3. **confidence/letter split.** `engine1.GRADE_TO_CONFIDENCE` was hand-rolled
   and drifted a full sub-tier low (B → 0.55, which `grade_thresholds.json`
   calls B-). FIX: confidence is now DERIVED from each grade's band MIDPOINT in
   `grade_thresholds.json` — one source of truth. Applying the threshold table
   to any grade's displayed confidence resolves back to the same letter (proven
   for all 11 grades in `tests/unit/mlbGradeDegradation.test.js`).

   > ### ⚠️ CORRECTION (Session 63, 2026-07-19) — THE "25/25 AGREEMENT" WAS A TAUTOLOGY
   >
   > **Do not cite the 25/25 grade↔confidence agreement below as validation of
   > grade quality. It validates nothing.**
   >
   > The fix above made `confidence` a *deterministic function of the letter*:
   > engine1 picks a letter via an additive factor index, then looks up that
   > letter's band midpoint to produce the number (`engine1.js:29-36`). Feeding
   > that number back through the same table can only ever return the letter it
   > came from. **The round-trip would report 25/25 even if every grade were
   > wrong.**
   >
   > It is a real fix for a real bug (the two encodings had drifted a sub-tier
   > apart) — it is simply a *consistency* check, not an *accuracy* check.
   > `confidence` carries ZERO information beyond the letter. The genuinely
   > independent probability is `p_win` (the quantile estimate over real game
   > logs), which Session 63 discovered had never been computed in production at
   > all. Payloads now carry `confidence_basis: 'grade_band'` so no consumer can
   > mistake the derived number for a model probability.
   >
   > Full diagnosis: `specs/audit-data/grade-collapse.md`.

## Blast radius (commit `9fc4edf`) — work-order #6
The degraded grades (projection=0 → `model_value = 0`) are already settled in
the append-only `ledger_entries` and are NOT deleted. Functional marking:
`getModelAggregate` now filters `.gt('model_value', 0)` on the settled AND
pending queries — the rows stay in the ledger but leave the public model record
(their hit/miss is noise, not skill). Post-fix no new such row can be written.

**Exact count NOT queryable from the dev box** (`*.supabase.co` is unreachable
here — curl 000; only `vyndr.app`/`api.vyndr.app` resolve; no `VYNDR_INTERNAL_KEY`
locally). Proxy signal: 9/25 (36%) of the current live slate. For the precise
figure, run in Supabase SQL:
```sql
SELECT count(*) FILTER (WHERE outcome IS NOT NULL) AS settled_degraded,
       count(*)                                    AS total_degraded
FROM ledger_entries
WHERE user_id IS NULL AND model_value = 0;
```

## Other sports — work-order #5
NBA/WNBA/soccer grade through the SAME `analyzeViaEngine1` → `engine1` path
(`gradeSlateService` does not branch by sport; `mlbGrader.js` is dead code). So
they SHARE the disease and are fixed by the same commit. They rarely grade in
prod today (stats service offline off-season → refuse anyway). No separate fix.

## Live validation — work-order #4
The fix deploys immediately, but the SNAPSHOT only re-grades on the full cron
(UTC hours 14,19,22,1,3). Run after the next 14:00 UTC snapshot post-deploy:
```
node scripts/validate-grade-fix.js
```
PASS criteria: projection==0 count → 0; edge_pct no longer contains 100 and is
not the four-value cluster; grade↔confidence agreement 25/25. The before-state
(this file's "Before") is the diff baseline; the script's output is the
fingerprint.

## AFTER — VALIDATED LIVE (2026-07-17 14:00:53 UTC regrade, fingerprint)
Ran `scripts/validate-grade-fix.js` against the first post-deploy snapshot.

| Signal | Before (03:00 UTC) | After (14:00 UTC) |
|---|---|---|
| projection == 0 | **9 / 25** | **0 / 25** ✅ |
| grade ↔ confidence agree | 15 / 25 (4-letter); 0/25 vs 11-step | **25 / 25** ✅ |
| edge_pct distinct values | 4 — {20, 60, 100, 140} | 7 — {20, 60, 70, 76, 78, 82, 100} ✅ |
| projection distribution | contained 0 | all positive (min 0.09, no zeros) ✅ |

The nine projection-0 grades vanished (those props now refuse). Grade and
confidence agree on every row. Edges are continuous, not the degenerate cluster.
The single remaining 100 is NOT the old bug: Wilyer Abreu · hits · line 0.5 ·
**projection 1.0** · over → `(1.0 − 0.5)/0.5 = 100%`, a real model call of double
a small line. The `(model − line)/line` metric inherently produces large % on
0.5-step lines — the frontend `|edge| > 40` guard is the intended safety net for
exactly that, and it stays. **All three bugs resolved; validated in production.**