rlmesh_remote_vector_env_cancel_handle
Env construction connects; Model construction only validates. Remote I/O is exclusive, while immutable accessors/cancellation may overlap any call. Accessor pointers remain borrowed until free, including after close.
RLMeshStatus rlmesh_remote_vector_env_cancel_handle(
const RLMeshRemoteVectorEnv* remote_vector_env,
RLMeshExtCancelToken** out
)