Read integrity, as-of context, and the shadow matchup resolve (A1-A7)

Seven orders of measurement-first repair. The served grade does not move.

A0/A1 — the unordered page walk returned the right COUNT and the wrong ROWS:
410-617 of 2,490 duplicated with an equal number never returned, while
rows.length matched the server exactly. safePaginate orders on a real unique
key, verifies the tuple at runtime, and THROWS on a query error instead of
treating it as end-of-data. Both hits PROVES are withdrawn: they were drawn
through that reader, and defense_by_direction's distinct-n was likely below
the gate floor all along.

A2/A2b — rolled across every reader: 11 FAIL -> 0. Composite keys pulled from
pg_index (the context tables are dated-composite and had no single unique
column). The unordered helper is deleted, not parked.

A3 — ledgerService and retentionService defaulted the SAME env var to
DIFFERENT versions, so no ledger row ever carried the marker eligibility
requires. One source now. model_snapshots settlement moved onto the cron:
15,484 -> 28,894 settled, repaired-champion 0 -> 7,556.

A4 — hitsFactorContext takes an as-of cutoff. Refusal over reconstruction: no
row at-or-before the date means the factor does not apply, never the nearest
row. Live path unchanged, proven 400/400 on real rows.

A5 — factor_inputs freezes what the factor READ, never the multiplier, so an
audit can recompute and check. It also recorded the finding: the three hits
factors have NEVER fired. prop.opponent and prop.opposing_pitcher are read by
the resolver and written by nothing.

A6/A7 — matchupKeys resolves those keys from the posted lineup plus the
schedule's probable pitchers, and fires the factors into a SHADOW freeze:
248 fires on 308 props, 245 of which would move the grade. The served
forecast is untouched. specs/a8-shadow-factor-gate.md pre-registers the test
that decides whether they ever go live.

Nothing is turned on. CALIBRATION_DEPLOYED stays []. Both verdicts stay
withdrawn. 4,772 tests / 371 suites green, web build exit 0, read-integrity
harness 34/34.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

scripts/champion-ablation.js

@@ -51,6 +51,8 @@
 
 require('dotenv').config();
 const { createClient } = require('@supabase/supabase-js');
+const { paginate } = require('../src/utils/safePaginate');
+const { uniqueKeyFor } = require('../src/utils/tableKeys');
 
 const SB_URL = process.env.SUPABASE_URL;
 const SB_KEY = process.env.SUPABASE_SERVICE_ROLE_KEY || process.env.SUPABASE_SERVICE_KEY;
@@ -143,20 +145,39 @@ function bootstrapCorr(rows, key, seed = 20260804, iters = 3000) {
   };
 }
 
-async function page(sb, table, select, apply) {
-  const out = [];
-  for (let from = 0; ; from += PAGE) {
-    let q = sb.from(table).select(select);
-    q = apply(q).range(from, from + PAGE - 1);
-    const { data, error } = await q;
-    if (error) throw error;
-    if (!data || data.length === 0) break;
-    out.push(...data);
-    if (data.length < PAGE) break;
-  }
-  return out;
+// ── FIX A2 (2026-08-09) — THE SAFE WALK ───────────────────────────────────
+// `page()` above walks with no ORDER BY. Measured on production, that returned
+// the correct row COUNT and the wrong ROWS: up to 33.6% of a read came back
+// twice while an equal share never came back at all. `pageSafe` routes the same
+// call through `src/utils/safePaginate`, which orders on a UNIQUE key on every
+// page, verifies uniqueness at runtime, and THROWS on a query error instead of
+// treating it as end-of-data.
+//
+// `page()` SURVIVES only for the context tables (statcast_aggregates,
+// batter_spray, team_defense, platoon_splits, park_dimensions, game_context...).
+// Those have COMPOSITE primary keys with no single unique column, so
+// safePaginate cannot express them. They measure 0% corruption today; making
+// them safe needs a composite-key ordering the helper does not yet have. Do not
+// use `page()` for ledger_entries or model_snapshots.
+async function pageSafe(sb, table, select, apply, key = uniqueKeyFor(table)) {
+  return paginate(() => apply(sb.from(table).select(select)),
+    { key, pageSize: PAGE, label: `${table}` });
 }
 
+/** THE MEASURED READS — main() and the harness call the same functions. */
+const READS_LEDGER = {
+  ledger: (sb) => pageSafe(sb, 'ledger_entries',
+    'id, player_key, stat, line, side, game_date, outcome, quarantine_reason',
+    (q) => q.eq('sport', 'mlb').is('user_id', null).in('outcome', ['hit', 'miss'])),
+};
+
+/** THE MEASURED READS — main() and the harness call the same functions. */
+const READS = {
+  snaps: (sb) => pageSafe(sb, 'model_snapshots',
+    'id, player_key, stat, line, side, game_date, p_win, features, quarantine_reason, captured_at, archetype',
+    (q) => q.eq('sport', 'mlb').not('p_win', 'is', null).not('features', 'is', null)),
+};
+
 const propKey = (r) => `${r.player_key}|${r.stat}|${Number(r.line)}|${String(r.side).toLowerCase()}|${r.game_date}`;
 
 /**
@@ -170,10 +191,8 @@ const propKey = (r) => `${r.player_key}|${r.stat}|${Number(r.line)}|${String(r.s
  * this run is read-only.
  */
 async function fetchAll(sb) {
-  const snaps = await page(sb, 'model_snapshots',
-    'player_key, stat, line, side, game_date, p_win, features, quarantine_reason, captured_at, archetype',
-    (q) => q.eq('sport', 'mlb').not('p_win', 'is', null).not('features', 'is', null));
-  const led = await page(sb, 'ledger_entries', 'player_key, stat, line, side, game_date, outcome, quarantine_reason',
+  const snaps = await READS.snaps(sb);
+  const led = await pageSafe(sb, 'ledger_entries', 'id, player_key, stat, line, side, game_date, outcome, quarantine_reason',
     (q) => q.eq('sport', 'mlb').is('user_id', null).in('outcome', ['hit', 'miss']));
 
   const outcomeBy = new Map();
@@ -371,4 +390,9 @@ async function main() {
   process.exit(0);
 }
 
-main().catch((e) => { console.error(e); process.exit(1); });
+if (require.main === module) {
+  main().catch((e) => { console.error(e); process.exit(1); });
+}
+
+// Exported so the read-integrity harness measures THE REAL FUNCTION.
+module.exports = { READS, READS_LEDGER };