embedded3: cut predictor convection carries ρ (host + e3_cut.cu; density-scaling pin); operator load route includes the wall exchange (exchange.rs); reconstructed_parts, probe aperture floor knob; dfg_split diagnostic test

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

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

@@ -13,6 +13,16 @@ use super::body::Body;
 use super::field::Field;
 use super::wall::{FaceKind, Mask, linear_fit, stencil_nodes, z_planes};
 
+/// Minimum face aperture for a velocity node to enter a probe's
+/// interpolation (`RTX_E3_PROBE_MIN_APERTURE`, default 0.5; 0 keeps every
+/// fluid face, the reading before S2-1's fix).
+fn probe_min_aperture() -> f64 {
+    std::env::var("RTX_E3_PROBE_MIN_APERTURE")
+        .ok()
+        .and_then(|v| v.parse().ok())
+        .unwrap_or(0.5)
+}
+
 #[derive(Debug, Clone, Copy, PartialEq)]
 pub struct SurfaceForce {
     pub f: [f64; 3],
@@ -154,10 +164,16 @@ impl Mask {
             let foot_c = (foot.0, foot.1, if zq == z { foot.2 } else { zq });
             let nodes = stencil_nodes((x, y, zq), c, g, self.periodic_z(), |_| None);
             let values: &[f64] = [&f.u, &f.v, &f.w][c];
+            // A cut face's velocity lives on the open part of the face, not
+            // at its centre: a node whose centre lies in the body would put
+            // the wall profile's value h/2 too deep and bias the wall
+            // gradient at O(1). Nodes below the minimum aperture are dropped
+            // and the point's own wall intercept takes their place.
+            let min_aperture = probe_min_aperture();
             let fluid = |idx: usize| match c {
-                0 => self.u_kind(idx) == FaceKind::Fluid,
-                1 => self.v_kind(idx) == FaceKind::Fluid,
-                _ => self.w_kind(idx) == FaceKind::Fluid,
+                0 => self.u_kind(idx) == FaceKind::Fluid && self.a_u(idx) >= min_aperture,
+                1 => self.v_kind(idx) == FaceKind::Fluid && self.a_v(idx) >= min_aperture,
+                _ => self.w_kind(idx) == FaceKind::Fluid && self.a_w(idx) >= min_aperture,
             };
             if nodes.iter().all(|n| fluid(n.idx)) {
                 out[c] = nodes.iter().map(|n| n.weight * values[n.idx]).sum();