generate.c: use SeeFastSign instead of full SEE for check-block sign check

Non-losing-block-of-check scoring only ever consumed SEE()'s sign
(>= 0 vs < 0), never the magnitude -- exactly the case SeeFastSign()
already exists for. Avoids building/sorting both sides' attacker
lists and discovering x-rays whenever the defending side has no
attacker on the destination square at all.

Verified via precommit_check.sh (self-test + DEBUG smoke test) and
the three curated ECM suites at sd 10 against head_reference: no
regression (ringers 4/11 vs 3/11, confident_quick 73/90 vs 70/90,
hard_quick 17/90 vs 18/90, the latter delta within this suite's known
noise floor).

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

1 files changed, 1 insertions, 1 deletions

diff --git a/src/generate.c b/src/generate.c
index 7e8f43e..dd9fba5 100644
--- a/src/generate.c
+++ b/src/generate.c
@@ -4469,7 +4469,7 @@ Return value:
                     {
                         // 0..2400
                         s += (VALUE_QUEEN - PIECE_VALUE(mv.pMoved)) * 4;
-                        if (SEE(pos, mv) >= 0)
+                        if (SeeFastSign(pos, mv))
                         {
                             // Non-losing block of check
                             ASSERT(SEE(pos, mv) == 0);