Commands: fail summon when a mod rejects a mob or minecart

Return None when a spawn's join callback removes the mob, propagate it through summon, and flush minecart joins before reporting success while watching the new cart's ID.

Fixes #7184

Co-Authored-By: Codex <[email protected]>

crates/horizon-client/src/game/commands.rs

@@ -2175,7 +2175,8 @@ impl Game<'_> {
             if self.ui.difficulty == 0 && t.category == "monster" {
                 return Err(err("commands.summon.failed.peaceful", &[]));
             }
-            self.spawn_mob_spawned(&short, pos);
+            self.spawn_mob_spawned(&short, pos)
+                .ok_or_else(|| err("commands.summon.failed.uuid", &[]))?;
             name = Text::translate(&entity_name_key(&kind), &[]);
         } else {
             match short.as_str() {
@@ -2250,7 +2251,11 @@ impl Game<'_> {
                         let empty = horizon_world::nbt::Tag::Compound(Default::default());
                         cart.spawner = Some(Box::new(Spawner::load(&empty)));
                     }
+                    let id = cart.id;
                     self.carts.push(cart);
+                    if !self.native_joins_flush(false, id) {
+                        return Err(err("commands.summon.failed.uuid", &[]));
+                    }
                     name = Text::translate(&format!("entity.minecraft.{k}"), &[]);
                 }
                 // SummonCommand.createEntity: any other type from an empty compound.

crates/horizon-client/src/game/creatures.rs

@@ -427,6 +427,9 @@ impl Game<'_> {
         let id = mob.id;
         self.mobs.push(mob);
         self.native_mobs_joined(self.mobs.len() - 1, false);
+        if !self.mobs.iter().any(|m| m.id == id) {
+            return None;
+        }
         self.enchant_spawn_equipment(id);
         self.halloween_spawn_head(id);
         if !persistent && !scripted {