FireX: Merge with firemodels/master

.github/workflows/Line_Endings.yml

@@ -21,7 +21,7 @@ jobs:
     # Steps represent a sequence of tasks that will be executed as part of the job
     steps:
       # Checks-out your repository under $GITHUB_WORKSPACE, so your job can access it
-      - uses: actions/checkout@v6
+      - uses: actions/checkout@v7
 
       - name: Check for CRLF line endings
         run: |

.github/workflows/cmake.yml

@@ -91,7 +91,7 @@ jobs:
         sudo apt-get -y update
         sudo apt-get -y install libopenmpi-dev openmpi-bin
 
-    - uses: actions/checkout@v6
+    - uses: actions/checkout@v7
     - run: git config --global --add safe.directory /__w/fds/fds
 
     - name: set linux-gnu compiler
@@ -165,7 +165,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     steps:
       - name: Checkout code
-        uses: actions/checkout@v6
+        uses: actions/checkout@v7
 
       - name: install openmpi
         run: brew install gcc@15 open-mpi
@@ -243,7 +243,7 @@ jobs:
         shell: cmd
 
     steps:
-    - uses: actions/checkout@v6
+    - uses: actions/checkout@v7
 
       # install oneapi components from web installer based on
       # oneapi-ci/scripts/install_windows.bat

.github/workflows/linux.yml

@@ -39,7 +39,7 @@ jobs:
           mkl@2026.0.0
         prune: false       
 
-    - uses: actions/checkout@v6
+    - uses: actions/checkout@v7
 
     - name: build fds debug
       run: |
@@ -74,7 +74,7 @@ jobs:
           mkl@2025.1.0
         prune: false  
 
-    - uses: actions/checkout@v6
+    - uses: actions/checkout@v7
     - name: build fds debug
       run: |
         source /opt/intel/oneapi/setvars.sh
@@ -96,7 +96,7 @@ jobs:
     runs-on: [ubuntu-latest]
 
     steps:
-    - uses: actions/checkout@v6
+    - uses: actions/checkout@v7
 
     - uses: actions/setup-python@v6
       with:

.github/workflows/osx.yml

@@ -34,7 +34,7 @@ jobs:
         shell: bash
 
     steps:
-    - uses: actions/checkout@v6
+    - uses: actions/checkout@v7
     - name: install openmpi
       run: |
         brew install gcc@15 open-mpi

.github/workflows/windows.yml

@@ -42,7 +42,7 @@ jobs:
         shell: cmd
 
     steps:
-    - uses: actions/checkout@v6
+    - uses: actions/checkout@v7
 
       # install oneapi components from web installer based on
       # oneapi-ci/scripts/install_windows.bat

Source/ccib.f90

@@ -6,13 +6,33 @@
 !
 MODULE CC_SCALARS
 
-USE COMPLEX_GEOMETRY
+USE COMPLEX_GEOMETRY, ONLY: GEOMEPS,LOOSEPS,GEOFCT,NGUARD,CCGUARD,CC_GASPHASE,CC_CUTCFE,CC_SOLID, &
+     CC_INBOUNDARY,CC_UNDEFINED,CC_VGSC,CC_EGSC,CC_IDCE, &
+     CC_FGSC,CC_IDCF,CC_IDRC,CC_UNKF,CC_CGSC,CC_IDCC,CC_UNKZ,CC_UNKH,CC_ETYPE_RGGAS, &
+     CC_ETYPE_CFGAS,CC_FTYPE_RGGAS,CC_FTYPE_CFGAS,CC_FTYPE_CFINB,CC_FTYPE_SVERT,CC_FTYPE_RCGAS, &
+     CC_FTYPE_CCGAS,CC_ETYPE_SCINB,CC_ETYPE_RCGAS,CC_ETYPE_EP,CC_MATVEC_DEFINED,NM_START, &
+     CALL_FOR_GLMAT,CALL_FROM_GLMAT_SETUP,N_REQ11,N_REQ12,N_REQ112,N_REQ13,REQ11,REQ112,REQ12,REQ13, &
+     WRITE_SET_CUTCELLS_TIMINGS,N_SET_CUTCELLS_3D_CALLS,SET_CUTCELLS_TIME_INDEX,GET_CARTCELL_CUTCELLS_TIME_INDEX, &
+     CC_SET_DATA_TIME_INDEX,INIT_CUTCELL_DATA_TIME_INDEX,CCCOMPUTE_RADIATION_TIME_INDEX, &
+     CC_DENSITY_TIME_INDEX,CC_VELOCITY_FLUX_TIME_INDEX,CC_COMPUTE_VISCOSITY_TIME_INDEX, &
+     CC_DIVERGENCE_PART_1_TIME_INDEX,CC_END_STEP_TIME_INDEX,CC_NO_FLUX_TIME_INDEX, &
+     CC_COMPUTE_VELOCITY_ERROR_TIME_INDEX,MESH_CC_EXCHANGE_TIME_INDEX,T_CC_USED, &
+     VAL_TESTX_LOW,VAL_TESTX_HIGH,VAL_TESTY_LOW,VAL_TESTY_HIGH,VAL_TESTZ_LOW,VAL_TESTZ_HIGH, &
+     LU_SETCC,SEARCH_OTHER_MESHES_FACE,POINT_IN_POLYGON
+USE COMPLEX_GEOMETRY_GRID, ONLY: DELTA_INT,DELTA_VERT,DIST_THRES,FDS_AREA_GEOM,INDEX_UNDEFINED,INT_N_EXT_PTS, &
+     INT_P_IND,INT_TMP_IND,INT_VEL_IND,INT_RHO_IND,INT_H_IND,INT_RSUM_IND,INT_MU_IND,INT_MUDNS_IND, &
+     INT_RHO0_IND,INT_WCEN_IND,INT_VELS_IND,MAX_INTERP_POINTS,NQT2C,N_CUTCELLS_PROC,N_INB_CUTFACES_PROC, &
+     N_INT_CVARS,N_INT_CCVARS,N_REG_CUTFACES_PROC,N_LINK_ATTMP_F,GLOBAL_DELTA_CELL,GLOBAL_DELTA_EDGE, &
+     GLOBAL_DELTA_FACE,SET_CUTCELLS_3D,BLOCK_CC_SOLID_EXTWALLCELLS,INIT_CFACE_CELL,GET_REGULAR_CUT_EDGES_BC, &
+     GET_SOLID_CUTCELL_EDGES_BC,GET_BACK_CFACE_INDEX
 USE PRECISION_PARAMETERS
 USE GLOBAL_CONSTANTS
 USE MESH_POINTERS
 USE MESH_VARIABLES, ONLY: MESHES, MESH_TYPE
 USE COMP_FUNCTIONS, ONLY: CURRENT_TIME, GET_FILE_NUMBER
 USE MATH_FUNCTIONS, ONLY: GET_SCALAR_FACE_VALUE
+USE MEMORY_FUNCTIONS, ONLY: ALLOCATE_STORAGE
+USE GEOMETRY_FUNCTIONS, ONLY: SEARCH_OTHER_MESHES
 
 IMPLICIT NONE (TYPE,EXTERNAL)
 PRIVATE
@@ -117,10 +137,225 @@ MODULE CC_SCALARS
           FINISH_CC, INIT_CUTCELL_DATA,MESH_CC_EXCHANGE,NUMBER_UNKH_CUTCELLS,&
           ROTATED_CUBE_ANN_SOLN,ROTATED_CUBE_VELOCITY_FLUX,ROTATED_CUBE_RHS_ZZ,&
           SET_EXIMADVFLX_3D,SET_EXIMDIFFLX_3D,SET_EXIMRHOHSLIM_3D,&
-          SET_EXIMRHOZZLIM_3D,UNSTRUCTURED_POISSON_RESIDUAL,UNSTRUCTURED_POISSON_RESIDUAL_RC
+          SET_EXIMRHOZZLIM_3D,UNSTRUCTURED_POISSON_RESIDUAL,UNSTRUCTURED_POISSON_RESIDUAL_RC,&
+          INITIALIZE_BACK_CFACE_EXCHANGE,EXCHANGE_BACK_CFACE_DATA
+
+! Persistent layout for the per-step cross-mesh BACK CFACE gas-side data exchange (see INITIALIZE_BACK_CFACE_EXCHANGE
+! and EXCHANGE_BACK_CFACE_DATA). N_CF_BACK_SEND/RECV are the per-process query totals on the requester/owner side.
+LOGICAL, SAVE :: CF_BACK_EXCHANGE_ACTIVE=.FALSE.
+INTEGER, SAVE :: N_CF_BACK_SEND=0,N_CF_BACK_RECV=0
+INTEGER, SAVE, ALLOCATABLE, DIMENSION(:) :: CF_BACK_SEND_CNT3,CF_BACK_SDISPL3,CF_BACK_RECV_CNT3,CF_BACK_RDISPL3
+INTEGER, SAVE, ALLOCATABLE, DIMENSION(:) :: CF_BACK_SEND_NOM,CF_BACK_MAP_IDX     !< Requester side: owner mesh and back CFACE index per query
+INTEGER, SAVE, ALLOCATABLE, DIMENSION(:) :: CF_BACK_RECV_NOM,CF_BACK_RECV_IDX    !< Owner side: owner mesh and resolved local CFACE index per query
 
 CONTAINS
 
+! ------------------------ INITIALIZE_BACK_CFACE_EXCHANGE ---------------------------
+SUBROUTINE INITIALIZE_BACK_CFACE_EXCHANGE
+
+INTEGER :: NM,NOM,IQ,NQ,IIO,JJO,KKO,NOM2,ICFACE,SURF_B,FRONT,OD_INDEX,N_RESOLVED,N_GLOBAL,IP,K,P,TOTAL_SEND,TOTAL_RECV,IERR
+REAL(EB) :: POS(3)
+INTEGER,  ALLOCATABLE :: SEND_CNT(:),RECV_CNT(:),SDISPL(:),RDISPL(:),CNT3_S(:),CNT3_R(:),DSP3_S(:),DSP3_R(:),COUNTER(:)
+INTEGER,  ALLOCATABLE :: SEND_NOM(:),RECV_NOM(:),REPLY_IDX(:),REPLY_SURF(:),REPLY_DIM(:), &
+                         REPLY_BACK(:),REPLY_BSURF(:),REPLY_BDIM(:),MAP_NM(:),MAP_FRONT(:)
+REAL(EB), ALLOCATABLE :: SEND_POS(:),RECV_POS(:)
+
+N_RESOLVED = 0
+ALLOCATE(SEND_CNT(0:N_MPI_PROCESSES-1)) ; SEND_CNT = 0
+DO NM=LOWER_MESH_INDEX,UPPER_MESH_INDEX
+   DO NOM=1,NMESHES
+      IF (NOM==NM) CYCLE
+      NQ = MESHES(NM)%OMESH(NOM)%N_CFACE_QUERY
+      IF (NQ==0) CYCLE
+      IF (PROCESS(NOM)==MY_RANK) THEN  ! Owner is on this process: resolve directly.
+         DO IQ=1,NQ
+            POS(1:3) = MESHES(NM)%OMESH(NOM)%CFACE_QUERY_XYZ(IAXIS:KAXIS,IQ)
+            CALL SEARCH_OTHER_MESHES(POS(1),POS(2),POS(3),NOM2,IIO,JJO,KKO)
+            IF (NOM2/=NOM) CYCLE
+            ICFACE = GET_BACK_CFACE_INDEX(NOM,IIO,JJO,KKO,POS,-1,-1)
+            IF (ICFACE>0) THEN
+               FRONT    = MESHES(NM)%OMESH(NOM)%CFACE_QUERY_FRONT(IQ)
+               OD_INDEX = MESHES(NM)%CFACE(FRONT)%OD_INDEX
+               IF (OD_INDEX>0) THEN
+                  MESHES(NM)%BOUNDARY_ONE_D(OD_INDEX)%BACK_MESH  = NOM
+                  MESHES(NM)%BOUNDARY_ONE_D(OD_INDEX)%BACK_INDEX = ICFACE
+                  MESHES(NM)%BOUNDARY_ONE_D(OD_INDEX)%BACK_SURF  = MESHES(NOM)%CFACE(ICFACE)%SURF_INDEX
+                  N_RESOLVED = N_RESOLVED + 1
+               ENDIF
+            ENDIF
+         ENDDO
+      ELSE  ! Owner on another process: count for the all-to-all exchange below.
+         SEND_CNT(PROCESS(NOM)) = SEND_CNT(PROCESS(NOM)) + NQ
+      ENDIF
+   ENDDO
+ENDDO
+
+CROSS_PROCESS_IF: IF (N_MPI_PROCESSES>1) THEN
+
+   ALLOCATE(RECV_CNT(0:N_MPI_PROCESSES-1)) ; RECV_CNT = 0
+   CALL MPI_ALLTOALL(SEND_CNT,1,MPI_INTEGER,RECV_CNT,1,MPI_INTEGER,MPI_COMM_WORLD,IERR)
+
+   ALLOCATE(SDISPL(0:N_MPI_PROCESSES-1),RDISPL(0:N_MPI_PROCESSES-1))
+   ALLOCATE(CNT3_S(0:N_MPI_PROCESSES-1),CNT3_R(0:N_MPI_PROCESSES-1))
+   ALLOCATE(DSP3_S(0:N_MPI_PROCESSES-1),DSP3_R(0:N_MPI_PROCESSES-1))
+   SDISPL(0) = 0 ; RDISPL(0) = 0
+   DO IP=1,N_MPI_PROCESSES-1
+      SDISPL(IP) = SDISPL(IP-1) + SEND_CNT(IP-1)
+      RDISPL(IP) = RDISPL(IP-1) + RECV_CNT(IP-1)
+   ENDDO
+   TOTAL_SEND = SDISPL(N_MPI_PROCESSES-1) + SEND_CNT(N_MPI_PROCESSES-1)
+   TOTAL_RECV = RDISPL(N_MPI_PROCESSES-1) + RECV_CNT(N_MPI_PROCESSES-1)
+   CNT3_S = 3*SEND_CNT ; CNT3_R = 3*RECV_CNT ; DSP3_S = 3*SDISPL ; DSP3_R = 3*RDISPL
+   ALLOCATE(SEND_NOM(MAX(TOTAL_SEND,1)),SEND_POS(MAX(3*TOTAL_SEND,1)),MAP_NM(MAX(TOTAL_SEND,1)), &
+            MAP_FRONT(MAX(TOTAL_SEND,1)),REPLY_BACK(MAX(TOTAL_SEND,1)),REPLY_BSURF(MAX(TOTAL_SEND,1)), &
+            REPLY_BDIM(MAX(TOTAL_SEND,1)))
+   ALLOCATE(RECV_NOM(MAX(TOTAL_RECV,1)),RECV_POS(MAX(3*TOTAL_RECV,1)),REPLY_IDX(MAX(TOTAL_RECV,1)), &
+            REPLY_SURF(MAX(TOTAL_RECV,1)),REPLY_DIM(MAX(TOTAL_RECV,1)))
+   ALLOCATE(COUNTER(0:N_MPI_PROCESSES-1)) ; COUNTER = SDISPL
+
+   ! Pack cross-process queries grouped by destination process (matching the SDISPL ordering). MAP_NM and
+   ! MAP_FRONT record the local front CFACE associated with each query so the reply can be applied in order.
+   DO NM=LOWER_MESH_INDEX,UPPER_MESH_INDEX
+      DO NOM=1,NMESHES
+         IF (NOM==NM) CYCLE
+         IF (PROCESS(NOM)==MY_RANK) CYCLE
+         NQ = MESHES(NM)%OMESH(NOM)%N_CFACE_QUERY
+         IF (NQ==0) CYCLE
+         IP = PROCESS(NOM)
+         DO IQ=1,NQ
+            P = COUNTER(IP) + 1 ; COUNTER(IP) = P
+            SEND_NOM(P)         = NOM
+            SEND_POS(3*P-2:3*P) = MESHES(NM)%OMESH(NOM)%CFACE_QUERY_XYZ(IAXIS:KAXIS,IQ)
+            MAP_NM(P)           = NM
+            MAP_FRONT(P)        = MESHES(NM)%OMESH(NOM)%CFACE_QUERY_FRONT(IQ)
+         ENDDO
+      ENDDO
+   ENDDO
+   CALL MPI_ALLTOALLV(SEND_NOM,SEND_CNT,SDISPL,MPI_INTEGER,RECV_NOM,RECV_CNT,RDISPL,MPI_INTEGER,MPI_COMM_WORLD,IERR)
+   CALL MPI_ALLTOALLV(SEND_POS,CNT3_S,DSP3_S,MPI_DOUBLE_PRECISION,RECV_POS,CNT3_R,DSP3_R,MPI_DOUBLE_PRECISION,&
+                      MPI_COMM_WORLD,IERR)
+
+   ! Owner side: resolve each received query against its local cut-face data.
+   DO K=1,TOTAL_RECV
+      NOM = RECV_NOM(K)
+      POS(1:3) = RECV_POS(3*K-2:3*K)
+      CALL SEARCH_OTHER_MESHES(POS(1),POS(2),POS(3),NOM2,IIO,JJO,KKO)
+      ICFACE = 0 ; SURF_B = 0
+      IF (NOM2==NOM) ICFACE = GET_BACK_CFACE_INDEX(NOM,IIO,JJO,KKO,POS,-1,-1)
+      IF (ICFACE>0) SURF_B = MESHES(NOM)%CFACE(ICFACE)%SURF_INDEX
+      REPLY_IDX(K)  = ICFACE
+      REPLY_SURF(K) = SURF_B
+      REPLY_DIM(K)  = 0 ; IF (ICFACE>0) REPLY_DIM(K) = MESHES(NOM)%N_CFACE_CELLS_DIM
+   ENDDO
+
+   ! Reverse all-to-all: return the resolved BACK CFACE index, SURF_INDEX and owner CFACE dimension to requesters.
+   CALL MPI_ALLTOALLV(REPLY_IDX, RECV_CNT,RDISPL,MPI_INTEGER,REPLY_BACK, SEND_CNT,SDISPL,MPI_INTEGER,MPI_COMM_WORLD,IERR)
+   CALL MPI_ALLTOALLV(REPLY_SURF,RECV_CNT,RDISPL,MPI_INTEGER,REPLY_BSURF,SEND_CNT,SDISPL,MPI_INTEGER,MPI_COMM_WORLD,IERR)
+   CALL MPI_ALLTOALLV(REPLY_DIM, RECV_CNT,RDISPL,MPI_INTEGER,REPLY_BDIM, SEND_CNT,SDISPL,MPI_INTEGER,MPI_COMM_WORLD,IERR)
+
+   ! Requester side: store BACK_MESH / BACK_INDEX / BACK_SURF and allocate a ghost CFACE (with its boundary
+   ! storage) in MESHES(NOM) so the per-step exchange can deposit the back gas-side state and the solid heat
+   ! transfer solver can read it exactly as it reads a same-mesh back CFACE.
+   DO P=1,TOTAL_SEND
+      ICFACE = REPLY_BACK(P)
+      IF (ICFACE>0) THEN
+         NM       = MAP_NM(P)
+         FRONT    = MAP_FRONT(P)
+         NOM      = SEND_NOM(P)
+         SURF_B   = REPLY_BSURF(P)
+         OD_INDEX = MESHES(NM)%CFACE(FRONT)%OD_INDEX
+         IF (OD_INDEX>0) THEN
+            MESHES(NM)%BOUNDARY_ONE_D(OD_INDEX)%BACK_MESH  = NOM
+            MESHES(NM)%BOUNDARY_ONE_D(OD_INDEX)%BACK_INDEX = ICFACE
+            MESHES(NM)%BOUNDARY_ONE_D(OD_INDEX)%BACK_SURF  = SURF_B
+            N_RESOLVED = N_RESOLVED + 1
+            ! Allocate the ghost CFACE once per (NOM,ICFACE).
+            IF (.NOT.ALLOCATED(MESHES(NOM)%CFACE)) THEN
+               MESHES(NOM)%N_CFACE_CELLS_DIM = REPLY_BDIM(P)
+               ALLOCATE(MESHES(NOM)%CFACE(0:MESHES(NOM)%N_CFACE_CELLS_DIM))
+            ENDIF
+            IF (ICFACE>UBOUND(MESHES(NOM)%CFACE,1)) THEN
+               CALL ALLOCATE_STORAGE(NOM,CFACE_INDEX=ICFACE,SURF_INDEX=SURF_B)
+            ELSEIF (MESHES(NOM)%CFACE(ICFACE)%B1_INDEX<=0) THEN
+               CALL ALLOCATE_STORAGE(NOM,CFACE_INDEX=ICFACE,SURF_INDEX=SURF_B)
+            ENDIF
+         ENDIF
+      ENDIF
+   ENDDO
+
+   ! Define exchange layout so EXCHANGE_BACK_CFACE_DATA can move the back gas-side state every step.
+   N_CF_BACK_SEND = TOTAL_SEND
+   N_CF_BACK_RECV = TOTAL_RECV
+   ALLOCATE(CF_BACK_SEND_CNT3(0:N_MPI_PROCESSES-1),CF_BACK_SDISPL3(0:N_MPI_PROCESSES-1))
+   ALLOCATE(CF_BACK_RECV_CNT3(0:N_MPI_PROCESSES-1),CF_BACK_RDISPL3(0:N_MPI_PROCESSES-1))
+   CF_BACK_SEND_CNT3 = CNT3_S ; CF_BACK_SDISPL3 = DSP3_S
+   CF_BACK_RECV_CNT3 = CNT3_R ; CF_BACK_RDISPL3 = DSP3_R
+   ALLOCATE(CF_BACK_SEND_NOM(MAX(TOTAL_SEND,1)),CF_BACK_MAP_IDX(MAX(TOTAL_SEND,1)))
+   ALLOCATE(CF_BACK_RECV_NOM(MAX(TOTAL_RECV,1)),CF_BACK_RECV_IDX(MAX(TOTAL_RECV,1)))
+   IF (TOTAL_SEND>0) THEN
+      CF_BACK_SEND_NOM(1:TOTAL_SEND) = SEND_NOM(1:TOTAL_SEND)
+      CF_BACK_MAP_IDX(1:TOTAL_SEND)  = REPLY_BACK(1:TOTAL_SEND)
+   ENDIF
+   IF (TOTAL_RECV>0) THEN
+      CF_BACK_RECV_NOM(1:TOTAL_RECV) = RECV_NOM(1:TOTAL_RECV)
+      CF_BACK_RECV_IDX(1:TOTAL_RECV) = REPLY_IDX(1:TOTAL_RECV)
+   ENDIF
+   N_GLOBAL = TOTAL_SEND
+   CALL MPI_ALLREDUCE(MPI_IN_PLACE,N_GLOBAL,1,MPI_INTEGER,MPI_SUM,MPI_COMM_WORLD,IERR)
+   IF (N_GLOBAL>0) CF_BACK_EXCHANGE_ACTIVE = .TRUE.
+
+   DEALLOCATE(RECV_CNT,SDISPL,RDISPL,CNT3_S,CNT3_R,DSP3_S,DSP3_R,COUNTER,SEND_NOM,SEND_POS,MAP_NM,MAP_FRONT, &
+              REPLY_BACK,REPLY_BSURF,REPLY_BDIM,RECV_NOM,RECV_POS,REPLY_IDX,REPLY_SURF,REPLY_DIM)
+
+ENDIF CROSS_PROCESS_IF
+DEALLOCATE(SEND_CNT)
+
+!IF (N_RESOLVED>0) &
+!   WRITE(LU_ERR,'(A,I0,A,I0)') ' BACK CFACE exchange: process ',MY_RANK,' resolved cross-mesh back CFACEs: ',N_RESOLVED
+
+END SUBROUTINE INITIALIZE_BACK_CFACE_EXCHANGE
+
+
+! ------------------------ EXCHANGE_BACK_CFACE_DATA --------------------------------
+SUBROUTINE EXCHANGE_BACK_CFACE_DATA
+
+INTEGER :: K,P,NOM,ICFACE,B1,IERR
+REAL(EB), ALLOCATABLE :: SBUF(:),RBUF(:)
+
+IF (.NOT.CF_BACK_EXCHANGE_ACTIVE .OR. N_MPI_PROCESSES==1) RETURN
+ALLOCATE(SBUF(MAX(3*N_CF_BACK_RECV,1))) ; SBUF = 0._EB
+ALLOCATE(RBUF(MAX(3*N_CF_BACK_SEND,1))) ; RBUF = 0._EB
+
+! Owner side: pack the back gas-side state of each resolved CFACE.
+DO K=1,N_CF_BACK_RECV
+   ICFACE = CF_BACK_RECV_IDX(K)
+   IF (ICFACE<=0) CYCLE
+   NOM = CF_BACK_RECV_NOM(K)
+   B1  = MESHES(NOM)%CFACE(ICFACE)%B1_INDEX
+   IF (B1<=0) CYCLE
+   SBUF(3*K-2) = MESHES(NOM)%BOUNDARY_PROP1(B1)%TMP_G
+   SBUF(3*K-1) = MESHES(NOM)%BOUNDARY_PROP1(B1)%HEAT_TRANS_COEF
+   SBUF(3*K  ) = MESHES(NOM)%BOUNDARY_PROP1(B1)%Q_RAD_IN
+ENDDO
+CALL MPI_ALLTOALLV(SBUF,CF_BACK_RECV_CNT3,CF_BACK_RDISPL3,MPI_DOUBLE_PRECISION, &
+                   RBUF,CF_BACK_SEND_CNT3,CF_BACK_SDISPL3,MPI_DOUBLE_PRECISION,MPI_COMM_WORLD,IERR)
+
+! Requester side: deposit the received state into the ghost CFACE so the solver reads it like a same-mesh back CFACE.
+DO P=1,N_CF_BACK_SEND
+   ICFACE = CF_BACK_MAP_IDX(P)
+   IF (ICFACE<=0) CYCLE
+   NOM = CF_BACK_SEND_NOM(P)
+   B1  = MESHES(NOM)%CFACE(ICFACE)%B1_INDEX
+   IF (B1<=0) CYCLE
+   MESHES(NOM)%BOUNDARY_PROP1(B1)%TMP_G           = RBUF(3*P-2)
+   MESHES(NOM)%BOUNDARY_PROP1(B1)%HEAT_TRANS_COEF = RBUF(3*P-1)
+   MESHES(NOM)%BOUNDARY_PROP1(B1)%Q_RAD_IN        = RBUF(3*P)
+ENDDO
+DEALLOCATE(SBUF,RBUF)
+
+END SUBROUTINE EXCHANGE_BACK_CFACE_DATA
+
+
 ! ------------------------ COPY_UNST_DM_TO_CART -------------------------------------
 
 SUBROUTINE COPY_UNST_DM_TO_CART(NM)
@@ -3722,6 +3957,9 @@ SUBROUTINE MESH_CC_EXCHANGE(CODE)
 INTEGER :: EP,INPE,INT_NPE_LO,INT_NPE_HI,VIND,ICELL,IEDGE,IFEP
 REAL(EB) :: TNOW,TINTP
 
+! On the end-of-step (CODE=6) exchange, move the gas-side state of cross-mesh BACK CFACEs.
+IF (CODE==6) CALL EXCHANGE_BACK_CFACE_DATA
+
 ! For solid phase only return. All variables exchanged currently here are gas-phase.
 IF (SOLID_PHASE_ONLY) RETURN
 ! In case of initialization code from main return.