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, 20 insertions, 4 deletions

diff --git a/src/split.c b/src/split.c
index 17b77f6..8bc4e60 100755
--- a/src/split.c
+++ b/src/split.c
@@ -604,6 +604,9 @@ Return value:
             g_SplitInfo[u].sCounters.tree.u64TotalNodeCount = 0;
             g_SplitInfo[u].sCounters.tree.u64BetaCutoffs = 0;
             g_SplitInfo[u].sCounters.tree.u64BetaCutoffsOnFirstMove = 0;
+            g_SplitInfo[u].sCounters.tree.u64LeftoverTries = 0;
+            g_SplitInfo[u].sCounters.tree.u64LeftoverAlpha = 0;
+            g_SplitInfo[u].sCounters.tree.u64LeftoverFH = 0;
             g_SplitInfo[u].PV[0] = NULLMOVE;
 
             //
@@ -628,9 +631,10 @@ Return value:
                 // work for naught.  We also want to know as soon as
                 // possible so that we can vacate this split point,
                 // free up a worker thread and get back to the main
-                // search.  So forget about the leftover-selection
-                // budget (NumLeftoverMovesToSelect in search.c) here
-                // and sort the whole list of moves from best..worst.
+                // search.  So sort the whole list of moves from
+                // best..worst (search.c's main loop does the same
+                // unconditionally now too -- see its retired
+                // NumLeftoverMovesToSelect budget comment).
                 //
                 SelectBestWithHistory(ctx, v);
                 ctx->sMoveStack.mvf[v].mv.bvFlags |=
@@ -761,6 +765,12 @@ Return value:
                 g_SplitInfo[u].sCounters.tree.u64BetaCutoffs;
             ctx->sCounters.tree.u64BetaCutoffsOnFirstMove =
                 g_SplitInfo[u].sCounters.tree.u64BetaCutoffsOnFirstMove;
+            ctx->sCounters.tree.u64LeftoverTries =
+                g_SplitInfo[u].sCounters.tree.u64LeftoverTries;
+            ctx->sCounters.tree.u64LeftoverAlpha =
+                g_SplitInfo[u].sCounters.tree.u64LeftoverAlpha;
+            ctx->sCounters.tree.u64LeftoverFH =
+                g_SplitInfo[u].sCounters.tree.u64LeftoverFH;
 #endif
             //
             // Pop off the split info ptr from the stack in the thread's
@@ -932,8 +942,14 @@ Return value:
         ctx->sCounters.tree.u64TotalNodeCount;
     g_SplitInfo[u].sCounters.tree.u64BetaCutoffs += 
         ctx->sCounters.tree.u64BetaCutoffs;
-    g_SplitInfo[u].sCounters.tree.u64BetaCutoffsOnFirstMove += 
+    g_SplitInfo[u].sCounters.tree.u64BetaCutoffsOnFirstMove +=
         ctx->sCounters.tree.u64BetaCutoffsOnFirstMove;
+    g_SplitInfo[u].sCounters.tree.u64LeftoverTries +=
+        ctx->sCounters.tree.u64LeftoverTries;
+    g_SplitInfo[u].sCounters.tree.u64LeftoverAlpha +=
+        ctx->sCounters.tree.u64LeftoverAlpha;
+    g_SplitInfo[u].sCounters.tree.u64LeftoverFH +=
+        ctx->sCounters.tree.u64LeftoverFH;
 
     //
     // TODO: Any other counters we care about?