PaperMC/paper-server/patches/sources/net/minecraft/world/entity/ConversionParams.java.patch

--- a/net/minecraft/world/entity/ConversionParams.java
+++ b/net/minecraft/world/entity/ConversionParams.java
@@ -12,4 +_,11 @@
     public interface AfterConversion<T extends Mob> {
         void finalizeConversion(T mob);
     }
+
+    // Paper start - entity zap event - allow conversion to be cancelled during finalization
+    @FunctionalInterface
+    public interface CancellingAfterConversion<T extends Mob> {
+        boolean finalizeConversionOrCancel(final T convertedEntity);
+    }
+    // Paper start - entity zap event - allow conversion to be cancelled during finalization
 }