ocean_state_seed_land_cells Subroutine

   subroutine ocean_state_seed_land_cells(state, grid)
      !! Hold land T-cells (`wet_mask==0`) at FINITE reference values so
      !! the masked dyn-core never evaluates `0*NaN` (a zeroed face metric
      !! times a NaN land contribution is still NaN).  Spec §13.3 /
      !! `land_mask_final_resolution.md` R-land-state:
      !!   * `h_layer` floored to `H_VANISHED` (never 0 — avoids 1/0);
      !!   * tracer content zeroed (`hTr = 0`, so `T = S = 0` — finite);
      !!   * layer + barotropic face velocities zeroed at land faces.
      !!
      !! The `(h, hTr) = (H_VANISHED, 0)` pair is the LAND-STATE CONTRACT:
      !! it is what every vanished-gated operator already holds a land
      !! column at, so a land column looks the same to the budget at the
      !! latch and at every later step.  `seed_land_tracer_hold_impl`
      !! carries the full statement and the history.
      !!
      !! Runs at SETUP, after `metrics_apply_land_mask` has derived
      !! `wet_u/wet_v`, BEFORE `ocean_state_enter_data`.  Plain host loops
      !! (pre-enter_data).  No-op for an all-wet domain (`wet_mask≡1`).
      type(ocean_state_t), intent(inout) :: state
      type(hgrid_t), intent(in) :: grid

      integer :: nz_ml, t

      associate (ms => state%multilayer)
         nz_ml = size(ms%h_layer, 3)

         ! Tracer content on land is ZERO — the state every vanished-gated
         ! operator (ALE remap first) holds a land column at, and therefore
         ! the state the budget latch must see.  Order-independent of the
         ! thickness floor below: neither reads the other.  See
         ! `seed_land_tracer_hold_impl`'s land-state contract.
         if (allocated(ms%tracers)) then
            do t = 1, size(ms%tracers)
               call seed_land_tracer_hold_impl(ms%tracers(t)%hTr, &
                                               ms%wet_mask, nz_ml)
            end do
         end if

         ! h_layer floor on land.
         call seed_land_h_floor_impl(ms%h_layer, ms%wet_mask, nz_ml)

         ! On a WET column, the inert fillers a rigid-top coordinate leaves
         ! inside the ice (and below the bed) are seeded with the IC's own
         ! `c(z)*h_min` — the concentration at the filler's depth, not its
         ! donor's.  Establish invariant I1′ (`hTr = h*c_live`) HERE, with
         ! the one definition (`rdb_vl_merge_content`, host twin because
         ! this runs before `enter_data`), so the budget latch sees the
         ! state every later step holds.  Column-conservative, so the
         ! latch's content is unchanged either way; this is about the
         ! seeded state satisfying the invariant, not about the budget.
         ! (Under the previous rule, I1, the first regrid ZEROED these
         ! fillers un-budgeted — `-1.604E-06` relative at step 1 on
         ! `cavity_sloping_lid_rest_zfixed.nml` — which is why this fence
         ! was a zeroing hold.)  Fenced to `z_fixed` x cavity so every
         ! other namelist's step-0 state is bit-identical.
         if (state%metrics%use_cavity .and. state%vcoord%coord_type == VCOORD_Z_FIXED) then
            call ms%enforce_vanished_content_host(size(ms%h_layer, 1), size(ms%h_layer, 2))
         end if

         ! Zero layer face velocities at land faces.
         call seed_land_face_vel_impl(ms%u_face_x_layer, state%metrics%wet_u, nz_ml)
         call seed_land_face_vel_impl(ms%v_face_y_layer, state%metrics%wet_v, nz_ml)
      end associate

      ! Zero the layer mass-transports + barotropic face velocities at land
      ! faces (the transports ride masked metrics anyway, but resetting them
      ! keeps the held land state internally consistent).
      call seed_land_face_vel_impl(state%multilayer%hu_face_x_layer, &
                                   state%metrics%wet_u, nz_ml)
      call seed_land_face_vel_impl(state%multilayer%hv_face_y_layer, &
                                   state%metrics%wet_v, nz_ml)
      call seed_land_face_vel_2d_impl(state%barotropic%u_face_x, state%metrics%wet_u)
      call seed_land_face_vel_2d_impl(state%barotropic%v_face_y, state%metrics%wet_v)
      call seed_land_face_vel_2d_impl(state%barotropic%hu_face_x, state%metrics%wet_u)
      call seed_land_face_vel_2d_impl(state%barotropic%hv_face_y, state%metrics%wet_v)

      ! `grid` is part of the setup contract (shapes come from the state
      ! allocations); not re-read here.
      associate (unused => grid%nx_total)
      end associate
   end subroutine ocean_state_seed_land_cells