engine_enter_data Subroutine

   subroutine engine_enter_data(engine, cfg)
      !! Map the ocean state onto the device, then (when `bt_halo > 0`)
      !! allocate + attach the wide-halo BT march-in workspace, then
      !! warm up the device-path halo exchanges (UCX cuda_ipc handle
      !! open, outside any timed region — see `driver_run_ocean`'s
      !! "Content-safety argument" comment, carried over unchanged).
      type(ocean_engine_t), intent(inout) :: engine
      type(config_t), intent(in) :: cfg

      call ocean_state_enter_data(engine%state)
      engine%state%dyn%bt_halo = cfg%ocean%bt%bt_halo
      if (cfg%ocean%bt%bt_halo > 0) then
         call ocean_dyn_enable_bt_wide(engine%state%dyn, engine%grid, &
                                       cfg%dx, cfg%dy, &
                                       cfg%ocean%grid%lon_west, &
                                       cfg%ocean%grid%lat_south, &
                                       cfg%ocean%grid%rad_earth, &
                                       cfg%ocean%grid%grid_config, &
                                       cfg%coriolis_f, &
                                       cfg%ocean%topo%coriolis_beta, &
                                       cfg%ocean%topo%coriolis_y_ref, &
                                       cfg%ocean%grid%coriolis_scheme, &
                                       omega=cfg%ocean%grid%omega)
      end if

      ! The prognostic exchange is a WARM-UP (it opens the device-path
      ! handles outside any timed region), but it is not content-neutral:
      ! at a step boundary the duplicated seam faces of `u` hold each
      ! tile's own update and the exchange overwrites them.  On a cold
      ! start that is harmless (the seed is seam-consistent); on a warm
      ! restart it rewrote the checkpointed state before the first step.
      ! Skip it there -- the first step's own exchange opens the handles.
      if (.not. engine%warm_restart) then
         call ocean_halo_exchange_ml_state(engine%state%multilayer)
      end if
      if (cfg%ocean%bt%n_inner >= 1) then
         call ocean_halo_bt_group_2d(engine%state%dyn%bt_work%bt_eta, &
                                     engine%state%dyn%bt_work%bt_ubt, &
                                     engine%state%dyn%bt_work%bt_vbt)
         call ocean_halo_face_x(engine%state%dyn%bt_work%bt_ubt)
         if (cfg%ocean%bt%bt_halo > 0) then
            call ocean_halo_bt_group_2d_wide( &
               engine%state%dyn%bt_wide%w_eta, &
               engine%state%dyn%bt_wide%w_ubt, &
               engine%state%dyn%bt_wide%w_vbt, &
               engine%state%dyn%bt_wide%ng_wide)
         end if
      end if

      engine%device_mapped = .true.
   end subroutine engine_enter_data