Dynamic move ordering overhaul: continuation-history, evidence-gated

countermove promotion, retired hung-piece-escape and NumLeftoverMovesToSelect.

Full session was built on a "measure the pick, not the game" methodology:
aggregate solve counts on curated suites are too noisy to tune move-ordering
knobs against, so most decisions here came from per-move fail-high/alpha-raise
rates at much larger sample sizes (leftover FH% instrumentation, a zero-
selection-budget diagnostic that isolates a single best-of-remaining pick,
and evidence-bucket calibration), not solve-count deltas alone. See
CLAUDE.md's "Dynamic move ordering experiments" section for the reusable
methodology and generate.c's _ScoreAllMoves comment for the resulting
ordering hierarchy.

Changes:
- Added g_ContinuationHistory: same growth/decay math as the existing
  g_HistoryCounters butterfly table, additionally keyed by the previous
  move, so its magnitude is self-calibrated rather than a hand-picked
  constant. Flat, sufficient response across a 256x scale sweep.
- Countermove-table matches now get a real GOOD_MOVE-tier promotion
  (previously the table was write-only, tracked for stats but never read
  for ordering), but only when the match's own accumulated
  history+continuation evidence clears COUNTERMOVE_EVIDENCE_THRESHOLD
  (10,000) -- a raw match with no track record was shown to perform
  identically to an ordinary leftover (~0.6-0.85% FH), so promoting on
  match alone would have repeated hung-piece-escape's mistake below.
- Retired hung-piece-escape's unconditional GOOD_MOVE-tier promotion.
  Evidence-calibration showed the overwhelming majority of triggers (a
  zero-evidence population 250-1000x larger than countermove's) performed
  at the plain-leftover baseline -- the promotion was mostly free tier-
  escape treatment for moves that hadn't earned it. Replaced with
  FLEE_BONUS, a flat same-tier nudge inside SelectBestWithHistory (never
  escapes GOOD_MOVE/leftover classification, unlike a generation-time
  promotion) at the magnitude found to plateau a same-tier-nudge sweep.
- Retired NumLeftoverMovesToSelect (the depth-indexed budget on how many
  leftover moves got a full selection scan before falling back to
  unsorted order). search.c's main move loop now always fully selects --
  the leftover pool was shown to contain real, findable signal a bailout
  budget was discarding for a node-count savings that didn't hold up net-
  net once measured by solve counts and fail-high rates rather than raw
  node counts (noisy on small suites independent of this change).
- Collapsed leftover-move instrumentation from sorted/raw pairs down to a
  single set now that "raw" (unsorted fallback) is structurally
  impossible; kept the countermove evidence-bucket calibration counters
  (ongoing check that COUNTERMOVE_EVIDENCE_THRESHOLD stays well-
  calibrated); removed the contested-node A/B harness and hung-piece
  evidence calibration now that the decisions they were built to inform
  are made.

Net effect on the three curated suites (sd 10): solve counts wash (tied,
+1, -1 across ringers/confident/hard), leftover fail-high rate improved
consistently on all three (the intended, directly-measured target of this
work). Not yet validated beyond sd 10 -- an sn-based run or
eval_tune/match_play.py head-to-head gate is the natural next check before
leaning on this as a proven strength gain rather than a directionally-
sound, sd-10-clean change.

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_014XePz6Sk4qQsTaP2jVJWJu

1 files changed, 44 insertions, 0 deletions

diff --git a/src/movesup.c b/src/movesup.c
index dec090c..33deae2 100755
--- a/src/movesup.c
+++ b/src/movesup.c
@@ -1017,11 +1017,36 @@ Return value:
     SCORE iVal;
     MOVE mv;
     MOVE_STACK_MOVE_VALUE_FLAGS mvfTemp;
+    MOVE mvLast;
+    ULONG uPrevContKey = 0;
+    FLAG fHaveContinuation = FALSE;
+    COOR cEnprise;
 
     ASSERT(ctx->sMoveStack.uBegin[ctx->uPly] <= uEnd);
     ASSERT(u >= ctx->sMoveStack.uBegin[ctx->uPly]);
     ASSERT(u < uEnd);
 
+    // Continuation history: "did a move like this tend to fail high
+    // right after a move like that?", keyed by (previous move, this
+    // move) at the same [piece][to] coarseness g_HistoryCounters
+    // already uses. Same accumulation/decay math as g_HistoryCounters
+    // (see _IncrementContinuationCounter/_DecrementContinuationCounter,
+    // dynamic.c) so its magnitude is empirically self-calibrated rather
+    // than a hand-picked constant -- a pair seen once contributes
+    // almost nothing, a pair that's fail-highed repeatedly at real
+    // depth naturally grows to compete with PSQT+history.
+    if ((ctx->uPly > 0) && (0 != (mvLast = (ctx->sPlyInfo[ctx->uPly - 1]).mv).uMove))
+    {
+        uPrevContKey = MOVE_TO_CONT_KEY(mvLast);
+        fHaveContinuation = TRUE;
+    }
+
+    // Flee-to-safety: a small, same-tier selection-time nudge (not a
+    // GOOD_MOVE promotion -- that class was retired, see generate.c's
+    // RETIRED comment) for a quiet move whose origin square is
+    // currently en prise.
+    cEnprise = FindEnprisePiece(ctx, ctx->sPosition.uToMove);
+
     //
     // Linear search from u..ctx->sMoveStack.uEnd[ctx->uPly] for the
     // move with the best value.
@@ -1031,6 +1056,16 @@ Return value:
     if (!IS_CAPTURE_OR_PROMOTION(mv))
     {
         iBestVal += g_HistoryCounters[mv.pMoved][mv.cTo];
+        if (TRUE == fHaveContinuation)
+        {
+            iBestVal += CONTINUATION_SCALE *
+                g_ContinuationHistory[(uPrevContKey * CONT_KEY_RANGE) +
+                                      MOVE_TO_CONT_KEY(mv)];
+        }
+        if (mv.cFrom == cEnprise)
+        {
+            iBestVal += FLEE_BONUS;
+        }
     }
     uLoc = u;
 
@@ -1041,6 +1076,15 @@ Return value:
         if (!IS_CAPTURE_OR_PROMOTION(mv))
         {
             iVal += g_HistoryCounters[mv.pMoved][mv.cTo];
+            if (TRUE == fHaveContinuation)
+            {
+                iVal += g_ContinuationHistory[(uPrevContKey * CONT_KEY_RANGE) +
+                                               MOVE_TO_CONT_KEY(mv)];
+            }
+            if (mv.cFrom == cEnprise)
+            {
+                iVal += FLEE_BONUS;
+            }
         }
         if (iVal > iBestVal)
         {