Stabilize GPU buffer lifecycle around regrid

AMSS_NCKU_source/bssn_cuda_ops.cu

@@ -1201,9 +1201,9 @@ int bssn_cuda_prolong3_pack(int wei,
   if (wei != 3 || !llbc || !uubc || !extc || !func || !llbf || !uubf || !extf || !funf || !llbp || !uubp || !SoA)
     return 1;
 
-  // The current input runs with equatorial symmetry enabled.
-  // The symmetry-aware prolong CUDA path is not numerically stable yet,
-  // so force a safe fallback to the original Fortran implementation.
+  // The symmetry-aware prolong CUDA path is still not equivalent to the
+  // active Cell/ghost_width=3 Fortran implementation, so keep the safe
+  // fallback for all symmetry-enabled cases.
   if (symmetry != 0)
     return 1;
 
@@ -1276,7 +1276,6 @@ int bssn_cuda_prolong3_pack(int wei,
 
   // Current CUDA prolong path only supports the same fast path as the
   // optimized Fortran code: interior stencil access without symmetry_bd().
-  // If the stencil touches the symmetry boundary, fall back to Fortran.
   if (ic_min - 2 < 1 || jc_min - 2 < 1 || kc_min - 2 < 1)
     return 1;