embedded3: study knobs — aperture_substeps (space-time sub-sampling), momentum_volume_cell_mean, RTX_E3_MERGE_FRACTION; all default off (refuted as the fresh-row residual's source)

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

crates/specialized/rtx-cfd/tests/embedded3_falsifier.rs

@@ -241,6 +241,14 @@ fn run(scheme: WallScheme, moving: bool, dt: f64, t_end: f64) -> Run {
                 z1: Side::Periodic,
                 ..Boundaries::default()
             },
+            max_surface_speed: Some(U_PEAK),
+            // `RTX_E3_SUBSTEPS`: intermediate geometries for the space-time apertures.
+            aperture_substeps: std::env::var("RTX_E3_SUBSTEPS")
+                .ok()
+                .and_then(|v| v.parse().ok())
+                .unwrap_or(0),
+            // `RTX_E3_CELL_MEAN=1`: the momentum volume from the two cells' fractions.
+            momentum_volume_cell_mean: std::env::var("RTX_E3_CELL_MEAN").is_ok_and(|v| v == "1"),
             ..Parameters::default()
         },
     );

crates/specialized/rtx-cfd/tests/embedded3_sphere/mod.rs

@@ -133,6 +133,7 @@ pub fn measure(n: usize, scheme: WallScheme, c: (f64, f64, f64)) -> Measurement
             tolerance: 1e-8,
             convection_scheme: ConvectionScheme::Upwind,
             wall_scheme: scheme,
+            momentum_volume_cell_mean: std::env::var("RTX_E3_CELL_MEAN").is_ok_and(|v| v == "1"),
             ..Parameters::default()
         },
     );