PaperMC/paper-server/patches/sources/net/minecraft/world/item/EndCrystalItem.java.patch

--- a/net/minecraft/world/item/EndCrystalItem.java
+++ b/net/minecraft/world/item/EndCrystalItem.java
@@ -30,7 +30,7 @@
         if (!iblockdata.is(Blocks.OBSIDIAN) && !iblockdata.is(Blocks.BEDROCK)) {
             return InteractionResult.FAIL;
         } else {
-            BlockPos blockposition1 = blockposition.above();
+            BlockPos blockposition1 = blockposition.above(); final BlockPos aboveBlockPosition = blockposition1; // Paper - OBFHELPER
 
             if (!world.isEmptyBlock(blockposition1)) {
                 return InteractionResult.FAIL;
@@ -47,12 +47,18 @@
                         EndCrystal entityendercrystal = new EndCrystal(world, d0 + 0.5D, d1, d2 + 0.5D);
 
                         entityendercrystal.setShowBottom(false);
+                        // CraftBukkit start
+                        if (org.bukkit.craftbukkit.event.CraftEventFactory.callEntityPlaceEvent(context, entityendercrystal).isCancelled()) {
+                            if (context.getPlayer() != null) context.getPlayer().containerMenu.sendAllDataToRemote(); // Paper - Fix inventory desync
+                            return InteractionResult.FAIL;
+                        }
+                        // CraftBukkit end
                         world.addFreshEntity(entityendercrystal);
                         world.gameEvent((Entity) context.getPlayer(), (Holder) GameEvent.ENTITY_PLACE, blockposition1);
                         EndDragonFight enderdragonbattle = ((ServerLevel) world).getDragonFight();
 
                         if (enderdragonbattle != null) {
-                            enderdragonbattle.tryRespawn();
+                            enderdragonbattle.tryRespawn(aboveBlockPosition); // Paper - Perf: Do crystal-portal proximity check before entity lookup
                         }
                     }