Struct MeshStreamHandle 

pub struct MeshStreamHandle { /* private fields */ }

FFI handle for an open stream against a MeshNode.

HandleGuard-protected. Without it, two distinct UAFs can fire: _node: Arc<MeshNode> keeps the underlying node alive but not the MeshStreamHandle Box itself — net_mesh_free(node_handle) could deallocate the node handle’s box while net_mesh_send was deref’ing &*node_handle for the Arc::ptr_eq check in handles_match. The same hazard applies to this stream handle’s own box: a concurrent net_mesh_stream_free while net_mesh_send was reading sh.stream / sh._node would UAF the dropped fields. The guard closes both: the box stays leaked across _free; ops register via try_enter and _free quiesces them via begin_free.