Redesign lazy/super-lazy eval margins with position-specific percentile

tables, and fix four real search/recognizer bugs found while validating it

Main theme: replace the flat, heavily-padded LAZY_EVAL_BASE_MARGIN /
SUPER_LAZY_MARGIN_BY_ARMY constants with per-material-bucket percentile
tables (king safety by attacker army, residual by own army, separate
tables for the lazy vs super-lazy baselines) derived from a 30k-position
calibration pool, targeting a measured ~1-1.5% exceeded-margin rate
instead of an unmeasured "add lots of headroom" floor. QSearch's
FUTILITY_BASE_MARGIN_LAZY/SUPERLAZY were re-derived to match the new,
now-meaningful (p50-based) iPositional this produces. Self-play confirms
the working tree beats both HEAD, a more liberal (~5% miss target)
variant, and a more conservative (near-zero miss) variant of the same
margin mechanism.

Along the way, an initial self-play regression (this margin work bundled
with several changes in one pass, one of which broke things) led to a
day of ZFS-snapshot bisection and then targeted DEBUG-build fuzzing
against a stratified 200k-position corpus (tests/cross_sectional_200k.ep_,
new), which is what actually found and fixed four distinct, real,
pre-existing engine bugs -- none of them related to the margin redesign
itself:

- searchsup.c (CommonSearchInit): three early-return paths (timer
  abort, draw, too-deep bailout) left a node's own PV[] row stale
  instead of clearing it, letting an ancestor's UpdatePV splice a
  leftover move from a completely unrelated node into the displayed
  PV -- root cause of a WalkPV/MakeMove assert ("moving a piece to
  capture, but nothing was on the target square").

- dynamic.c (RecordEnprisePieceAtPly): the two-slot en-prise dedup
  compared (square, piece) instead of square alone, so a same-square
  re-record with a different piece (legitimate -- a fail-high
  capture's victim is restored by UnmakeMove and can differ across
  calls at the same ply) shifted a duplicate square into both slots,
  tripping ValueOfMaterialInTroubleDespiteMove's two-distinct-squares
  assert.

- recogn.c (_RecognizeKBKP): the wrong-colored-bishop corner-fortress
  draw shortcut fired even when the weak side has its own pawn(s),
  which can hand the strong side real zugzwang resources the fortress
  logic doesn't account for -- produced a false hard draw bound where
  EGTB shows a near-forced loss.

- eval.c (_EvalPasserRacesAgainstLoneKings): a rook pawn's race was
  credited as winning even when the strong side's own king sits
  exactly on its own pawn's queening square (distance 0 specifically --
  adjacent is fine, the square is empty) -- a classic stalemate
  resource the race heuristic can't see. Only reachable through
  _RecognizeKPK's pawn-hash-cache-hit path, which is why
  testrecogn.c's TestRecognExhaustiveKPK reported "0 wrong" the whole
  time; extended it to cover both color assignments and the full board
  (no mirror-shortcut) and documented the remaining cache-hit coverage
  gap for a future session to close.

Also: match_play.py gains a local_ebf metric (geometric-mean of
depth-normalized node-growth ratios between consecutive completed
iterations) alongside the existing cumulative nodes**(1/depth) ebf,
which turned out to be misleading when comparing engines with
different lazy-exit aggressiveness -- and probe.c/hash.c pick up two
small, independently-found correctness fixes (TB root-probe promotion
piece missing its color bit; ASSERT(g_pHashTable) crashing on the
legitimate "--hash none" config) noticed along the way.

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

1 files changed, 16 insertions, 3 deletions

diff --git a/src/dynamic.c b/src/dynamic.c
index 9c68993..c64794a 100644
--- a/src/dynamic.c
+++ b/src/dynamic.c
@@ -471,14 +471,27 @@ Return value:
     ASSERT(p && IS_VALID_PIECE(p) && !IS_PAWN(p));
     ASSERT(GET_COLOR(p) == uExpectedMover);
 
-    if ((ctx->cEnprise[uPly][0] != cSquare) ||
-        (ctx->pEnprise[uPly][0] != p))
+    // 2026-09-18: dedup on SQUARE alone, not (square, piece) -- the
+    // two slots are meant to hold the last two DISTINCT en-prise
+    // squares (see ValueOfMaterialInTroubleDespiteMove's "two
+    // different pieces hanging" use, which ASSERTs the two recorded
+    // squares differ). A same-square re-record with a different
+    // recorded piece -- legitimate per this function's own doc
+    // comment (a fail-high capture's victim is restored to cSquare by
+    // UnmakeMove, and can differ across calls at the same ply) --
+    // used to compare piece identity too, so it shifted the old
+    // (cSquare, oldPiece) entry down into slot 1 instead of updating
+    // slot 0 in place, leaving BOTH slots holding the same square.
+    // Found via fuzzing tests/cross_sectional_200k.ep_ (DEBUG build,
+    // sd 3): tripped ValueOfMaterialInTroubleDespiteMove's
+    // ASSERT(c != c1) from a live QSearch call, not a display path.
+    if (ctx->cEnprise[uPly][0] != cSquare)
     {
         ctx->cEnprise[uPly][1] = ctx->cEnprise[uPly][0];
         ctx->pEnprise[uPly][1] = ctx->pEnprise[uPly][0];
         ctx->cEnprise[uPly][0] = cSquare;
-        ctx->pEnprise[uPly][0] = p;
     }
+    ctx->pEnprise[uPly][0] = p;
 }