embedded3 S2-2b-ii: DeviceCg::refresh (fine operator per step, hierarchy every K steps, z zeroed before the scatter) + gate test; the flag driver's correctors 3 / inner 1e-3 (residual remedy measured 7.6e-9 on the moving circle); residual study test

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

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

@@ -155,6 +155,8 @@ pub struct DeviceStep {
     initialized: bool,
     /// A static cut-cell mask's tables (item 9b), when the solver has one.
     cut: Option<cut::DeviceCut>,
+    /// Steps since the multigrid hierarchy was last rebuilt (moving bodies).
+    steps_since_hierarchy: usize,
 }
 
 impl DeviceStep {
@@ -210,6 +212,7 @@ impl DeviceStep {
             timers,
             initialized: false,
             cut,
+            steps_since_hierarchy: 0,
         }
     }
 

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

@@ -329,7 +329,26 @@ impl DeviceStep {
             fresh_cells = self.solver.rebuild_moving_mask(&mut field, dt, t_new);
             self.upload(&field);
             self.cut = DeviceCut::build(&self.solver, g, Phase::Projection, t_new);
-            self.cg = None;
+            // The operator: refreshed every step, the hierarchy every
+            // `RTX_E3_PRECOND_REFRESH` steps (default 10; 1 = rebuild always).
+            let every: usize = std::env::var("RTX_E3_PRECOND_REFRESH")
+                .ok()
+                .and_then(|v| v.parse().ok())
+                .unwrap_or(10)
+                .max(1);
+            self.steps_since_hierarchy += 1;
+            if self.steps_since_hierarchy >= every || self.cg_dt != dt {
+                self.cg = None;
+                self.steps_since_hierarchy = 0;
+            } else if let Some(cg) = self.cg.as_mut() {
+                let problem = self.solver.poisson_operator(g, dt);
+                let params = MultigridParameters {
+                    precision: self.solver.params.poisson_precision,
+                    smoother: self.solver.params.poisson_smoother,
+                    ..MultigridParameters::default()
+                };
+                cg.refresh(&problem, &params);
+            }
             rt.stream
                 .memcpy_dtod(&self.u, &mut self.u_star)
                 .expect("u*");