src: broadcast BC type codes with MPI_INTEGER in pre_process; pin residue broadcasts

pre_process sent the integer bc_x/y/z%beg/%end with mpi_p (an 8-byte real transfer over 4-byte integers - undefined behavior that happened to work by adjacency); simulation and post_process already used MPI_INTEGER. Also adds a test pinning the hand-written vb/ve and BC-code residue in pre/post so a merge conflict cannot silently drop them. Both from review.

Author: sbryngelson

src/pre_process/m_mpi_proxy.fpp

@@ -39,16 +39,20 @@ contains
             call MPI_BCAST(${VAR}$, 1, MPI_LOGICAL, 0, MPI_COMM_WORLD, ierr)
         #:endfor
 
-        ! manual: bc_x/y/z and domain bounds (registered as struct members, not in NAMELIST_VARS)
+        ! manual: domain bounds and wall temperatures (REAL struct members, not in NAMELIST_VARS)
         #:for VAR in [ 'x_domain%beg', 'x_domain%end', 'y_domain%beg',         &
             & 'y_domain%end', 'z_domain%beg', 'z_domain%end',                   &
-            & 'bc_x%beg', 'bc_x%end', 'bc_y%beg', 'bc_y%end',                  &
-            & 'bc_z%beg', 'bc_z%end', 'bc_x%Twall_in', 'bc_x%Twall_out',       &
+            & 'bc_x%Twall_in', 'bc_x%Twall_out',                                &
             & 'bc_y%Twall_in', 'bc_y%Twall_out', 'bc_z%Twall_in',              &
             & 'bc_z%Twall_out']
             call MPI_BCAST(${VAR}$, 1, mpi_p, 0, MPI_COMM_WORLD, ierr)
         #:endfor
 
+        ! manual: BC type codes (INTEGER struct members)
+        #:for VAR in [ 'bc_x%beg', 'bc_x%end', 'bc_y%beg', 'bc_y%end', 'bc_z%beg', 'bc_z%end']
+            call MPI_BCAST(${VAR}$, 1, MPI_INTEGER, 0, MPI_COMM_WORLD, ierr)
+        #:endfor
+
         ! wall-velocity members consumed by s_slip_wall/s_no_slip_wall on all ranks
         #:for DIM in ['x', 'y', 'z']
             #:for DIR in [1, 2, 3]

toolchain/mfc/params_tests/test_fortran_gen.py

@@ -605,3 +605,19 @@ def test_generate_bcast_fpp_lag_params_registry_walk():
     # Dead members must not appear
     for dead in ("T0", "Thost", "c0", "rho0", "x0"):
         assert f"lag_params%{dead}" not in sim, f"dead member lag_params%{dead} present in sim"
+
+
+def test_mpi_proxy_residue_pins_wall_velocity_and_bc_datatypes():
+    """The vb/ve wall-velocity broadcasts and integer BC datatypes live in
+    hand-written residue (not codegen); pin them so an edit or merge conflict
+    that drops them fails loudly."""
+    import pathlib
+
+    root = pathlib.Path(__file__).resolve().parents[3]
+    for target in ("pre_process", "post_process"):
+        src = (root / "src" / target / "m_mpi_proxy.fpp").read_text()
+        assert "bc_${DIM}$%vb${DIR}$" in src, f"{target}: vb broadcasts missing"
+        assert "bc_${DIM}$%ve${DIR}$" in src, f"{target}: ve broadcasts missing"
+        assert "'bc_x%beg', 'bc_x%end', 'bc_y%beg', 'bc_y%end', 'bc_z%beg', 'bc_z%end']" in src
+        seg = src.split("'bc_z%beg', 'bc_z%end']", 1)[1]
+        assert "MPI_INTEGER" in seg.split("#:endfor")[0], f"{target}: BC codes not MPI_INTEGER"