Wrap TileMap HashMaps in Arc for async pathfinding access

- Add Arc<AHashMap> wrapper around floor_tiles, fixture_tiles, item_tiles
- Copy-on-write semantics: Arc::make_mut clones only if other Arcs exist
- Add insert_floor, insert_fixture, insert_item, remove_item methods
- Add get_floor_mut, get_fixture_mut for visibility updates
- Update all mutation sites to use new TileMap methods
- Enables cheap Arc::clone for async pathfinding workers
- Single-threaded pathfinding: no clone, direct access
- Multi-threaded pathfinding: clone Arc, read without locks

src/world/generation/forestry.rs

@@ -167,7 +167,7 @@ pub fn generate_chunk_forrestry(
 
     let collected_updates = collected_tilemap_updates.into_inner().unwrap();
     for (ivec, data) in collected_updates {
-        tilemap.fixture_tiles.insert(ivec, data);
+        tilemap.insert_fixture(ivec, data);
     }
     if count > 0 {
         println!(

src/world/generation/terrain.rs

@@ -159,7 +159,7 @@ pub fn generate_chunk_terrain(
         .unwrap()
         .into_iter()
         .map(|(pos, data)| {
-            tilemap.floor_tiles.insert(pos, data);
+            tilemap.insert_floor(pos, data);
             pos
         })
         .collect();

src/world/tiles/tilemap.rs

@@ -1,5 +1,6 @@
 use ahash::AHashMap;
 use bevy::prelude::*;
+use std::sync::Arc;
 
 /// Packed floor tile data for efficient storage. ~35 bytes vs 76 bytes tuple.
 #[derive(Clone, Copy, Debug)]
@@ -170,12 +171,13 @@ impl FixtureTileData {
     }
 }
 
-/// Tile map with fast AHashMap for pathfinding lookups.
-#[derive(Resource, Default)]
+/// Tile map with Arc-wrapped HashMaps for async pathfinding access.
+/// Uses copy-on-write: Arc::make_mut clones only if other Arcs exist.
+#[derive(Resource, Clone, Default)]
 pub struct TileMap {
-    pub floor_tiles: AHashMap<IVec3, FloorTileData>,
-    pub fixture_tiles: AHashMap<IVec3, FixtureTileData>,
-    pub item_tiles: AHashMap<IVec3, Vec<u32>>,
+    pub floor_tiles: Arc<AHashMap<IVec3, FloorTileData>>,
+    pub fixture_tiles: Arc<AHashMap<IVec3, FixtureTileData>>,
+    pub item_tiles: Arc<AHashMap<IVec3, Vec<u32>>>,
 }
 
 impl TileMap {
@@ -202,4 +204,37 @@ impl TileMap {
     pub fn has_fixture(&self, pos: &IVec3) -> bool {
         self.fixture_tiles.contains_key(pos)
     }
+
+    #[inline]
+    pub fn insert_floor(&mut self, pos: IVec3, tile: FloorTileData) {
+        Arc::make_mut(&mut self.floor_tiles).insert(pos, tile);
+    }
+
+    #[inline]
+    pub fn insert_fixture(&mut self, pos: IVec3, tile: FixtureTileData) {
+        Arc::make_mut(&mut self.fixture_tiles).insert(pos, tile);
+    }
+
+    #[inline]
+    pub fn insert_item(&mut self, pos: IVec3, entity_id: u32) {
+        Arc::make_mut(&mut self.item_tiles)
+            .entry(pos)
+            .or_default()
+            .push(entity_id);
+    }
+
+    #[inline]
+    pub fn remove_item(&mut self, pos: &IVec3) -> Option<Vec<u32>> {
+        Arc::make_mut(&mut self.item_tiles).remove(pos)
+    }
+
+    #[inline]
+    pub fn get_floor_mut(&mut self, pos: &IVec3) -> Option<&mut FloorTileData> {
+        Arc::make_mut(&mut self.floor_tiles).get_mut(pos)
+    }
+
+    #[inline]
+    pub fn get_fixture_mut(&mut self, pos: &IVec3) -> Option<&mut FixtureTileData> {
+        Arc::make_mut(&mut self.fixture_tiles).get_mut(pos)
+    }
 }

src/world/tiles/visibility.rs

@@ -100,7 +100,7 @@ pub fn handle_tile_occlusion_updates(
     for (_, mut tile, pos) in floor_tiles.iter_mut() {
         if let Some(visibility) = update_map.get(&pos.translation.as_ivec3()) {
             tile.visible_range = *visibility;
-            if let Some(tile_data) = tilemap.floor_tiles.get_mut(&pos.translation.as_ivec3()) {
+            if let Some(tile_data) = tilemap.get_floor_mut(&pos.translation.as_ivec3()) {
                 tile_data.visible_range = *visibility;
             }
         }