evaluate leaf value before vcf

test f15

Rapfi/search/ab/search.cpp

@@ -640,6 +640,17 @@ Value search(Board &board, SearchStack *ss, Value alpha, Value beta, Depth depth
 
     // Dive into vcf search when the depth reaches zero (~17 elo)
     if (depth <= 0.0f) {
+        Value leafValue = Evaluation::evaluate<Rule>(board, alpha, beta);
+
+        // Update bound using standing pat
+        if (oppo5)
+            beta = std::min(beta, leafValue);
+        else
+            alpha = std::max(alpha, leafValue);
+        // Prune directly if the value is already outside the window
+        if (alpha >= beta)
+            return alpha;
+
         return oppo5 ? vcfdefend<Rule, NT>(board, ss, alpha, beta)
                      : vcfsearch<Rule, NT>(board, ss, alpha, beta);
     }