rdb_ocean_set_tracer Function

   function rdb_ocean_set_tracer(c_handle, name, name_len, data, nx_p, ny_p, nz_p) &
      result(status) bind(c, name="rdb_ocean_set_tracer")
      !! Set the tracer named `name` to `data` (its own units — degC for
      !! temperature, PSU for salinity) on the physical interior. Verbatim
      !! the recovered `ocean_set_tracer_impl` sequence, generalised from
      !! hardcoded S/T to any registered tracer BY NAME: flush the
      !! windowed-advection accumulator -> refresh host (need the LIVE
      !! `h_layer` to form `hTr = h_layer*value`) -> mutate `hTr` on the
      !! physical interior -> narrow-push `hTr` -> recompute `rho_layer`
      !! (pulled back to host so it stays authoritative).
      !! `OCEAN_STATUS_ERR_NOT_FOUND` if no registered tracer matches.
      type(c_ptr), intent(in), value :: c_handle
      integer(c_int), intent(in), value :: name_len
      character(kind=c_char), intent(in) :: name(name_len)
      integer(c_int), intent(in), value :: nx_p, ny_p, nz_p
      real(c_double), intent(in) :: data(nx_p, ny_p, nz_p)
      integer(c_int) :: status

      type(ocean_handle_t), pointer :: h
      character(len=:), allocatable :: fname
      integer :: ng, i, j, k, it, ierr_local

      status = resolve_ocean(c_handle, h)
      if (status /= OCEAN_STATUS_OK) return
      if (.not. shape_matches_interior(h, nx_p, ny_p, nz_p)) then
         call fail("rdb_ocean_set_tracer: shape mismatch against the physical interior", &
                   ierr_local, OCEAN_STATUS_ERR_BAD_SHAPE)
         status = int(ierr_local, c_int)
         return
      end if

      call c_to_f_string(name, name_len, fname)
      it = tracer_index_by_name(h, fname)
      if (it == 0) then
         call fail("rdb_ocean_set_tracer: no tracer named '"//fname//"'", &
                   ierr_local, OCEAN_STATUS_ERR_NOT_FOUND)
         status = int(ierr_local, c_int)
         return
      end if

      ! Drain any open windowed tracer-advection accumulation BEFORE
      ! reading/overwriting the tracer, so pending transport (accumulated
      ! against the OLD field) is never later applied to the NEW one.
      ! Hard no-op at dt_tracer_advect_ratio<=1 (default; bit-identical).
      call ocean_dyn_flush_tracer_window(h%grid, h%state%metrics, h%state%dyn, &
                                         h%state%continuity, h%state%multilayer, &
                                         bc=h%state%bc)
      call ocean_handle_refresh_host(h)

      ng = h%grid%nghost
      associate (hl => h%state%multilayer%h_layer, htr => h%state%multilayer%tracers(it)%hTr)
         do k = 1, nz_p
            do j = 1, ny_p
               do i = 1, nx_p
                  htr(ng + i, ng + j, k) = hl(ng + i, ng + j, k)*real(data(i, j, k), wp)
               end do
            end do
         end do
         !$acc update device(htr)
      end associate
      call ocean_eos_compute(h%state%eos, h%state%multilayer)
      associate (rl => h%state%multilayer%rho_layer)
         !$acc update self(rl)
      end associate
      h%host_is_current = .true.
      status = int(OCEAN_STATUS_OK, c_int)
   end function rdb_ocean_set_tracer