fix: always remesh gen-0 chunks to fix border face culling

Author: HTRMC

src/client/world/ChunkManager.zig

@@ -805,10 +805,12 @@ pub const ChunkManager = struct {
             // Apply the new mesh
             render_chunk_ptr.setMesh(result.mesh);
 
-            // A neighbor arrived while this chunk was being meshed — the mesh we just
-            // applied may have stale boundary faces. Queue a follow-up remesh now that
-            // the chunk is in .ready state (setMesh transitions to .ready).
-            if (render_chunk_ptr.needs_remesh.swap(false, .acq_rel)) {
+            // Initial mesh (gen 0) was generated on the worker before the RenderChunk
+            // existed in storage. Neighbors generated concurrently couldn't see this chunk,
+            // and this chunk's mesh may not have seen them. Always follow up with a remesh
+            // to capture all currently-loaded neighbors and fix boundary face culling.
+            // For subsequent meshes (gen > 0), only remesh if a neighbor arrived during meshing.
+            if (result.mesh_generation == 0 or render_chunk_ptr.needs_remesh.swap(false, .acq_rel)) {
                 self.queueChunkRemesh(result.pos);
             }