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/wall.rs

@@ -92,6 +92,11 @@ pub struct Mask {
     /// (`usize::MAX` = its own row) — a small cell shares its pressure
     /// unknown with its largest active face neighbour in the projection.
     pub(super) merge_master: Vec<usize>,
+    /// The predictor's convection scheme (the exchange route replicates
+    /// its limited fluxes on the faces next to prescribed ones).
+    pub(super) scheme: crate::solvers::incompressible::ConvectionScheme,
+    /// The fluid's density (the exchange route's convective flux).
+    pub(super) density: f64,
 }
 
 /// The z lattice position of a query: the lower plane index, the upper
@@ -502,6 +507,8 @@ impl Mask {
             step_apertures: None,
             step_open: None,
             merge_master: Vec::new(),
+            scheme: crate::solvers::incompressible::ConvectionScheme::Upwind,
+            density: 1.0,
         })
     }