fix: persist air supply across relog (#2646)

Air was not saved to NBT, causing it to reset to full on every
login. This allowed players to exploit drowning by relogging to
restore lost air bubbles.

pumpkin/src/entity/player.rs

@@ -4319,6 +4319,21 @@ impl NBTStorage for Player {
             // Store food level, saturation, exhaustion, and tick timer
             self.hunger_manager.write_nbt(nbt).await;
 
+            nbt.put_int(
+                "AirSupply",
+                self.breath_manager
+                    .air_supply
+                    .load(Ordering::Relaxed)
+                    .clamp(0, super::breath::MAX_AIR),
+            );
+            nbt.put_int(
+                "DrowningTick",
+                self.breath_manager
+                    .drowning_tick
+                    .load(Ordering::Relaxed)
+                    .clamp(0, super::breath::DROWNING_INTERVAL - 1),
+            );
+
             nbt.put_string(
                 "Dimension",
                 self.world().dimension.minecraft_name.to_string(),
@@ -4371,6 +4386,18 @@ impl NBTStorage for Player {
 
             self.hunger_manager.read_nbt(nbt).await;
 
+            if let Some(air) = nbt.get_int("AirSupply") {
+                self.breath_manager
+                    .air_supply
+                    .store(air.clamp(0, super::breath::MAX_AIR), Ordering::Relaxed);
+            }
+            if let Some(tick) = nbt.get_int("DrowningTick") {
+                self.breath_manager.drowning_tick.store(
+                    tick.clamp(0, super::breath::DROWNING_INTERVAL - 1),
+                    Ordering::Relaxed,
+                );
+            }
+
             // Load any saved spawnpoint data (SpawnX/SpawnY/SpawnZ, SpawnDimension, SpawnForced)
             if let (Some(x), Some(y), Some(z)) = (
                 nbt.get_int("SpawnX"),

pumpkin/src/world/mod.rs

@@ -3175,6 +3175,7 @@ impl World {
             .await;
 
         player.send_active_effects().await;
+        player.breath_manager.send_air_supply(player);
         self.send_player_equipment(player).await;
 
         if let crate::net::ClientPlatform::Java(java_client) = player.client.as_ref()