embedded3: the cut mask's imposition and the device surface-velocity tables restricted to a 4-cell band (deeper prescribed faces are never read; the surface velocity was the moving step's cost); the operator rebuild counted in the rebuild share

Co-Authored-By: Claude Fable 5.1 <[email protected]>

crates/specialized/rtx-cfd/src/solvers/incompressible/embedded3/step/device/cut.rs

@@ -107,7 +107,10 @@ impl DeviceCut {
                 .memcpy_stod(if v.is_empty() { &[0u32][..] } else { v })
                 .expect("upload")
         };
-        // Surface velocity at the foot per face, and the open flags.
+        // Surface velocity at the foot per face within the imposition band
+        // (zero beyond it: never read), and the open flags.
+        let band = mask.impose_band().unwrap_or(f64::INFINITY);
+        let dists: [&[f64]; 3] = [&cut.d_u, &cut.d_v, &cut.d_w];
         let mut ub: [Vec<f64>; 3] = [Vec::new(), Vec::new(), Vec::new()];
         let mut open: [Vec<i32>; 3] = [Vec::new(), Vec::new(), Vec::new()];
         for c in 0..3 {
@@ -127,7 +130,11 @@ impl DeviceCut {
                             (j as f64 + if c == 1 { 0.0 } else { 0.5 }) * h[1],
                             (k as f64 + if c == 2 { 0.0 } else { 0.5 }) * h[2],
                         ];
-                        ubc[idx] = mask.surface_velocity_at(body, x, c, t);
+                        ubc[idx] = if dists[c][idx].abs() <= band {
+                            mask.surface_velocity_at(body, x, c, t)
+                        } else {
+                            0.0
+                        };
                         opc[idx] = i32::from(if projection {
                             match c {
                                 0 => mask.u_open(idx),
@@ -315,7 +322,6 @@ impl DeviceStep {
                 .expect("w*");
         }
         let cptrs = self.cut.as_ref().expect("cut").ptrs();
-        let rebuild = t_rebuild.elapsed();
         if self.cg.is_none() || self.cg_dt != dt {
             let problem = self.solver.poisson_operator(g, dt);
             let params = MultigridParameters {
@@ -326,6 +332,7 @@ impl DeviceStep {
             self.cg = Some(DeviceCg::new(&problem, &params));
             self.cg_dt = dt;
         }
+        let rebuild = t_rebuild.elapsed();
         let anchor = self.solver.anchor_cell(g);
         let mut total = 0;
         let mut final_residual = f64::INFINITY;