Structural hardening: unknown-is-not-zero + takeability-is-book-identity

Both guards are ADDITIVE. The full suite (4,111 -> 4,126 tests, 331 suites)
passes unchanged through the migration, which is the evidence that no
currently-correct output moved: served path, champion, reference ruler and
the four accruing challengers are byte-identical.

GUARD 1 -- src/utils/known.js. Number(null)===0 has produced at least SIX
separate defects here, including one in a module written the same week its
author documented the trap. Per-module vigilance has demonstrably failed,
so the rule lives in one place and SEVEN sites now delegate: platoonSplits,
projectionChallenger, challengerProjection, contactChallenger,
statcastAggregateService, consensusRuler, gradeRanking -- plus
compoundTotalBases moved onto knownRate.

Two functions, deliberately: knownNumber (any finite number -- a REAL 0 is
a fact and must survive) and knownRate (non-negative, rejects booleans --
for counts/rates where `true` or -1 is broken, not thin). Collapsing them
is how the next variant gets in. firstKnown() exists because `a || b`
discards a measured 0 and `a ?? b` does not.

MY OWN GUARD HAD THE BUG IT EXISTS TO PREVENT, and its own test caught it:
Number([]) === 0, so an empty array coerced to a measured ZERO. Same trap
wearing a different type. Both helpers now reject objects outright.

GUARD 2 -- src/config/takeability.js. Takeability is BOOK IDENTITY and
never price shape. Baseball prop markets are genuinely thin, juiced and
one-sided, and all three are NORMAL structure: betrivers and hardrockbet
legitimately quote one side only (5 such rows surfaced in yesterday's
re-stamp), and a hits-over at -300 is a real placeable bet. A rule that
inferred un-takeability from price extremity or one-sidedness would throw
those away while still admitting a DFS book at an ordinary -119 -- exactly
backwards, because the -119 is the fake one.

THE DISTINCTION THAT MUST NOT COLLAPSE, now enforced by test:
  isTakeableMarket(book)  -- CAN it be bet?     (identity)
  isWithinPriceBand(odds) -- SHOULD we promote? (policy band, floor -160)
A -300 DraftKings prop is takeable AND out of band; a PrizePicks -119 is in
band AND not takeable. Independent axes.

FLAGGED, NOT SILENTLY CHANGED: the ledger's `takeable` column is the
PRICE-BAND answer, and its name predates this distinction. Four challengers
and the ranking gate read it, so renaming or redefining it is its own
order -- doing it here would have changed correct current behaviour under
cover of a hardening change.

Fixtures are REAL prod rows from the 2026-08-02 re-stamp, not invented.

Gates: 4,126 tests / 331 suites green; next build exit 0.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QJs13VsyiSKYQP6rj3NNmc

src/services/projectionChallenger.js

@@ -48,11 +48,13 @@ const STAT_FIELD = Object.freeze({
 });
 
 const isNum = (v) => typeof v === 'number' && Number.isFinite(v);
-const num = (v) => {
-  if (v == null || v === '') return null;
-  const n = typeof v === 'number' ? v : Number(v);
-  return Number.isFinite(n) ? n : null;
-};
+// MIGRATED to the shared guard (2026-08-02). `Number(null) === 0` has produced
+// at least SIX separate defects in this codebase, including one in a module
+// written the same week its author documented the trap — per-module vigilance
+// has demonstrably failed. Semantics are byte-identical to the local copy this
+// replaces, so no output changes; the point is that there is now ONE rule.
+const { knownNumber } = require('../utils/known');
+const num = knownNumber;
 const clamp = (v, lo, hi) => (v < lo ? lo : v > hi ? hi : v);
 const abbrOf = (team) => {
   if (!team) return null;