NNUE accumulator struct scaffolding; fix 3 bugs found by DEBUG+TEST; add that gate

Partial checkpoint on the nnue-accumulator-plumbing branch, before the
MakeMove/UnmakeMove hookup itself:

- chess.h: NNUE_ACCUMULATOR struct (256 floats, pre-activation, float32
  for now -- quantization to int16 deliberately deferred until a real
  quantization-aware export pass exists, per docs/NNUE.md). Added the
  live, always-current SEARCHER_THREAD_CONTEXT.sNnueAccum[2] (one per
  color) and PLY_INFO.sNnueAccumBackup (the king-move full-recompute
  backup slot, DEBUG-only color tag declared for a later ASSERT).
  LIGHTWEIGHT_SEARCHER_CONTEXT also mirrors sNnueAccum[2] at the same
  relative position -- omitting that broke its byte-compatible-prefix
  contract with the full context the moment MakeMove/UnmakeMove will
  start touching it unconditionally (caught by this session's own
  TestSan self-test failure).

- Combining DEBUG=1 and TEST=1 for the first time (apparently ever)
  while chasing that failure immediately turned up three more real,
  pre-existing bugs, all in self-test-only code whose assert-guarded
  invariants had never been checked with asserts actually compiled in:
    - board.c: IsBoardLegal now rejects an en passant square whose rank
      doesn't match the side to move (and verifies the double-moved
      pawn/empty origin square), closing a gap VALID_EP_SQUARE alone
      can't catch.
    - testgenerate.c: TestCapturesAndPromotionsGenerator's fixture table
      had a self-contradictory FEN this new IsBoardLegal check would
      have caught; replaced with a genuine Black-to-move en passant
      position.
    - testgenerate.c: TestFindUnblockedSquaresSpeed called
      _GenerateAllMoves directly instead of the GenerateMoves wrapper,
      skipping the DEBUG-only pStack->board[uPly] snapshot
      WouldGiveCheck's own ASSERT checks against.

- precommit_check.sh / CLAUDE.md: added the DEBUG=1 TEST=1 combination
  as a permanent third pre-commit gate, given what its first-ever run
  turned up. Real cost (~235s of ~266s total, unoptimized build
  dominates), judged worth it.

Co-Authored-By: Claude Sonnet 5 <[email protected]>

1 files changed, 28 insertions, 5 deletions

diff --git a/src/CLAUDE.md b/src/CLAUDE.md
index f2bbd37..c8e9c08 100644
--- a/src/CLAUDE.md
+++ b/src/CLAUDE.md
@@ -42,9 +42,9 @@ object mismatches at link time.
 
 ## Pre-commit testing
 
-Two cheap, complementary gates exist and should both be run before
+Three cheap, complementary gates exist and should all be run before
 committing a search/eval/move-generation change (not needed for pure
-doc/comment-only changes). Neither replaces the curated-suite/`sd`-`sn`
+doc/comment-only changes). None of these replace the curated-suite/`sd`-`sn`
 comparison workflow below -- these catch outright bugs (crashes, broken
 invariants) fast; the suite workflow measures whether a change is actually
 *better*, which is a slower, separate question.
@@ -61,7 +61,28 @@ invariants) fast; the suite workflow measures whether a change is actually
   original-2004-era and untouched since, but `testeval.c`/`testsearch.c`/
   `testsee.c` have been actively edited by recent sessions -- this is a
   live, working harness, not dead code, despite living outside the normal
-  build profile.
+  build profile. **Note this profile has no `DEBUG`, so every `ASSERT` in
+  these test files is a silent no-op** -- see the next gate.
+- **`gmake DEBUG=1 TEST=1` combined self-test.** Same self-test suite as
+  above, but with asserts actually compiled in. Added 2026-10-15 after
+  running this exact combination for the first time (ever, as far as
+  anyone could tell) immediately turned up three real, previously-
+  undiscovered bugs in one run -- none in production code, all in
+  self-test-harness code whose assert-guarded invariants had apparently
+  never been checked with asserts live: (1) `testgenerate.c`'s
+  `TestCapturesAndPromotionsGenerator` fixture table had a
+  self-contradictory hand-built FEN (en passant square on rank 6 paired
+  with Black to move -- only reachable with White to move; see `board.c`'s
+  `IsBoardLegal`, which now rejects this same mistake if it ever arrives
+  via `setboard`); (2) same file's `TestFindUnblockedSquaresSpeed` called
+  `_GenerateAllMoves` directly instead of the `GenerateMoves` wrapper,
+  skipping the DEBUG-only `pStack->board[uPly]` snapshot
+  `WouldGiveCheck`'s own `ASSERT(PositionsAreEquivalent(...))` checks
+  against. Budget real time for this step -- it's unoptimized (`DEBUG`
+  implies no `-O3`), so it dominates `precommit_check.sh`'s total runtime
+  (measured ~235s of ~266s total on this box, vs. ~16s for the plain
+  `TEST=1` gate) -- but kept anyway: the bug-catching rate on its first
+  ever run made the cost clearly worth it.
 - **`debug_smoke_test.sh [binary] [depth] [count]`** (defaults: `./_typhoon`,
   `sd 4`, 10 positions). Builds/runs a `DEBUG=1` binary (asserts compiled
   in) against a fresh random sample of positions drawn from the full
@@ -79,11 +100,13 @@ invariants) fast; the suite workflow measures whether a change is actually
   flushes the logfile every call) before triggering the `int3` breakpoint,
   so that text survives in the logfile even if stdout capture is lost to
   an abrupt `SIGTRAP` death.
-- **`precommit_check.sh`** runs both gates back-to-back and restores a
+- **`precommit_check.sh`** runs all three gates back-to-back and restores a
   normal release build afterward (`gmake clean` + the standard
   `GENETIC=1 PERF_COUNTERS=1 MP=1 SIXTYFOUR=1` profile), so the working
   directory isn't left with a `TEST`/`DEBUG`-flavored binary as a side
-  effect of running it. ~20s end to end on this box.
+  effect of running it. **~266s (~4.5min) end to end on this box** as of
+  adding the combined DEBUG+TEST gate (was ~20s with just the two original
+  gates) -- almost all of the increase is that one unoptimized step.
 
 **On not making this an automatic git pre-commit hook**: deliberately not
 wired up that way. Two concrns pushed toward manual-by-default: (1) each