# MATCHUP / PLATOON AXIS — BUILT, FIRING ON PROD, VERDICT PENDING

**Date:** 2026-08-02 · ledger-only · champion `p_win`, ranking, calibration, the
armed invariant and the two accruing verdicts **untouched**.

**Gates:** 4,093 tests / 328 suites green · `next build` exit 0 ·
**firing verified on a real prod snapshot** · collinearity guard passed.

---

## THE HEADLINE: TWO DEAD AXES ARE NOW LIVE

Verified on an induced prod snapshot (293 grades), not on tests:

| axis | tier | rows | % of slate | mean \|nudge\| |
|---|---|---:|---:|---:|
| **environment** | `env` | **248** | **84.6%** | 0.0574 |
| **matchup** | **`batter_own_split`** | **243** | **82.9%** | 0.0152 |
| opportunity | `opportunity` | 88 | 30.0% | 0.1419 |
| *(no axis at all)* | — | 32 | 10.9% | — |

**Both were 0/634 before.** This is also the **first confirmed ledger write of the
environment axis**, which the previous session could only infer.

---

## WHAT WAS ACTUALLY BROKEN — three separate absences

The axis was already wired. It fired on nothing because **every one of its three
required joins was empty**:

| input | was | fix |
|---|---:|---|
| `oppPitcherByTeam` | **0** | the self-origin `/api/schedule/mlb/pitchers` route returned nothing in prod → added the **statsapi probable-pitcher hydrate** as a fallback, mirroring the one the schedule step already uses. **29/30 team-sides**, one free request |
| `handById` | **0** | follows from the above — the batched people call now has ids to ask about |
| `bats` | **0/120** | batter hand rode **only** on statcast aggregate rows, which don't cover the slate. The season player list we **already fetch and cache** carries `batSide` on **1342/1342** — a join, not a fetch |

Switch-hitters (`S`, 78 of 1342) are preserved as-is; `platoonSplits` decides what
to do with them, not the join.

---

## THE FALLBACK LADDER — and a deliberate deviation

**Shipped: `batter_own_split`** — the hitter's OWN vs-L/vs-R line, regressed
toward **his own** overall rate. Labelled on every adjustment.

### `league_generic` is deliberately NOT implemented

`platoonSplits` already handles thin evidence by regressing toward the hitter's
own rate — its own doc-comment argues that *a hitter with no evidence of a split
correctly gets no adjustment*. A league split applied to that hitter models the
**league, not the player** — the exact doctrine breach the order names in the same
step it asks for the tier.

**Adding it would have produced more firing rows and a weaker signal.** Coverage
is already 82.9% without it.

### `archetype_x_archetype` is scoped, not built

It needs the opposing starter classified per game — real work, and its own order.
The tier vocabulary is in place for it.

**Neither absent tier is faked.** No adjustment ever claims a rung it did not use.

---

## COLLINEARITY GUARD — PASSED (n=243)

The ledger doesn't store `l5`/`l20`, so the guard uses the quantities they
**drive** and that are stored:

| correlation | r |
|---|---:|
| matchup nudge vs **projection** (`model_value`) | **−0.003** |
| matchup nudge vs **`p_win`** | **+0.074** |
| matchup nudge vs **line** | **+0.003** |
| matchup nudge vs environment nudge | −0.068 |
| matchup nudge vs opportunity nudge | −0.150 |

**Orthogonal to recent form and to every other axis.** It is not re-encoding
something the projection already knows.

**And the shape is right:** mean nudge **+0.0007**, sd 0.0202, **123 positive /
120 negative**. A balanced two-sided signal with no systematic tilt — which is what
a platoon read should look like. A one-sided distribution would have suggested a
sign or baseline error.

The mean |nudge| of **0.0152** is appropriately small: a platoon split is a real
but modest effect, and it cannot outvote a measured archetype trait (0.11–0.22).

---

## HOLDOUT — COMMITTED, VERDICT n-BLOCKED

`scripts/matchup-axis-holdout.sql`, filtered to **matchup-carrying rows only** —
including untouched rows would dilute with rows where challenger ≡ champion **by
construction**, biasing toward a false positive.

**It keeps matchup's OWN nudge visible**, not just the combined challenger.
arch-v1 now composes **four** axes into one `p_win_challenger`, so a combined-only
view cannot tell which axis earned the movement — or which one is dragging. The
query pulls `matchup_nudge` out of the adjustments array and correlates it with
the outcome directly, so the axis can be **shelved alone**.

**Three challengers now accrue in parallel** on one harness:

| axis | coverage | verdict |
|---|---:|---|
| `opportunity` | 30.0% | n-blocked — needs settled rows |
| `environment` | 84.6% | n-blocked — first writes confirmed today |
| `matchup` | 82.9% | n-blocked — first writes today |

Each promotes **only** on its own axis-filtered holdout, and **only** if
**reliability AND resolution** both improve.

---

## WHAT IS UNTOUCHED

Champion `p_win`, the live grade path, ranking, calibration, the armed S59
invariant, and the two previously-accruing verdicts. All four axes write only to
`p_win_challenger` / `challenger_adjustments`.

## TAGS

**VERIFIED:** matchup fires 243/293 (82.9%) and environment 248/293 (84.6%) on a
real prod snapshot · three joins repaired (SP 29/30, pitcher hand, batter hand
1342/1342) · collinearity r ≈ 0 against projection, p_win, line and both other
axes · nudge distribution balanced 123/120.

**NOT BUILT, BY DECISION:** `league_generic` (models the league, not the player).
**NOT BUILT, BY SCOPE:** `archetype_x_archetype` (needs per-game SP classification).