Plumb fThreat and attack snapshots into SPLIT_INFO (prep for step 4)

UNIFY_SEARCH.md step 3: add fThreat and the two attack-snapshot
bitboards (bbMinorAttacksSnapshot/bbRookAttacksSnapshot) to SPLIT_INFO
(chess.h), populated by StartParallelSearch (split.c) from values the
originating thread already has at split-launch time, passed through
from search.c's call site.

Plumbing only -- nothing reads these fields yet (HelpSearch() still
runs its own inline copy, untouched). That's step 4: unify
HelpSearch() onto SearchOneMove, at which point it can pass these
real values instead of the zeroed snapshots and missing fThreat its
current hand-rolled gate has.

Sequenced before step 4 deliberately (not combined or left for
after): landing the plumbing first means there's no window where
HelpSearch() calls the real CanWeReduceOrPruneMove()/ShouldLatePrune()
gate with stale/zeroed snapshots -- see UNIFY_SEARCH.md's note on why
that matters for FH_TABLE_COLLECTION's sampling.

Verified: precommit_check.sh passes. Bit-identical node counts at
sd10/--cpus 1 across all three curated suites, zero change (expected
-- single-threaded path never reads these new fields). cpus 4 smoke
run across all three suites: clean exits, no crashes.

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

1 files changed, 19 insertions, 1 deletions

diff --git a/src/split.c b/src/split.c
index 2997661..fd65f2b 100644
--- a/src/split.c
+++ b/src/split.c
@@ -472,7 +472,10 @@ StartParallelSearch(IN SEARCHER_THREAD_CONTEXT *ctx,
                     IN OUT MOVE *pmvBest,
                     IN ULONG uMoveNum,
                     IN INT iPositionExtend,
-                    IN ULONG uDepth)
+                    IN ULONG uDepth,
+                    IN FLAG fThreat,
+                    IN BITBOARD bbMinorAttacksSnapshot[2],
+                    IN BITBOARD bbRookAttacksSnapshot[2])
 {
 /**
 
@@ -500,6 +503,16 @@ Parameters:
     ULONG uMoveNum : in next move number in ctx->sMoveStack
     INT iPositionExtend : in position based extensions for split node
     ULONG uDepth : in the depth we need to search to
+    FLAG fThreat : in whether a node-wide threat extension is in play at
+                  the split point -- stashed into g_SplitInfo so a
+                  future HelpSearch() can call CanWeReduceOrPruneMove's
+                  real gate instead of its own hand-rolled approximation
+    BITBOARD bbMinorAttacksSnapshot[2] : in the originating thread's own
+                  attack-table snapshots (see search.c's
+                  fParentAttackTablesAreFresh) -- stashed into
+                  g_SplitInfo for the same reason as fThreat; helper
+                  threads have no other way to get a non-zero snapshot
+    BITBOARD bbRookAttacksSnapshot[2] : in, same as bbMinorAttacksSnapshot
 
 Return value:
 
@@ -576,6 +589,11 @@ Return value:
                    sizeof(POSITION));
             g_SplitInfo[u].iEval = ctx->sPlyInfo[ctx->uPly].iEval;
             g_SplitInfo[u].iImprovement = iImprovement;
+            g_SplitInfo[u].fThreat = fThreat;
+            g_SplitInfo[u].bbMinorAttacksSnapshot[WHITE] = bbMinorAttacksSnapshot[WHITE];
+            g_SplitInfo[u].bbMinorAttacksSnapshot[BLACK] = bbMinorAttacksSnapshot[BLACK];
+            g_SplitInfo[u].bbRookAttacksSnapshot[WHITE] = bbRookAttacksSnapshot[WHITE];
+            g_SplitInfo[u].bbRookAttacksSnapshot[BLACK] = bbRookAttacksSnapshot[BLACK];
             g_SplitInfo[u].eNodeType = ctx->sPlyInfo[ctx->uPly].eNodeType;
 #if DEBUG
             g_SplitInfo[u].uSplitPly = ctx->uPly;