embedded3 R6-1: the body's φ and the cut geometry on the device (RTX_E3_GEOM_DEVICE=1)

- e3_geom.cu: corner φ on the narrow band (the flag test's circle + capsule
  around the step's centreline polyline + span cuts + fillet union), face
  apertures / face-centre φ by the Kuhn triangles, cell volumes by the six
  Kuhn tets and wall vectors by closure — CutGeometry::build_from in fp64,
  host operation order, FMA contraction off.
- Body::with_device_sdf / DeviceSdf: the device form of φ (the host passes the
  polyline per step); the flag wake test attaches it (same arithmetic as its
  closure; the polylines factored out unchanged).
- step/device/geom.rs DeviceGeom: persistent φ / bound / volume / wall buffers;
  the face tables written straight into DeviceCut's predictor apertures and
  distances (update skips their scatters); the host mirror = the band's entries
  gathered compactly onto recycled arrays of retired device generations
  (GeomPool; band-list history) — Mask::from_cut classifies it.
- RTX_E3_BAND_CHECK=1 with the knob: mirror AND device tables against the host
  build_from bit for bit on every refresh.
- Knob off: byte-identical (slab ny 62 one period CSV = main's); host suite 21/21.

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>

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

@@ -124,7 +124,20 @@ impl Mask {
         b: Boundaries,
         prev: Option<(&CutGeometry, f64, f64)>,
     ) -> Result<Self, String> {
+        let lap = std::time::Instant::now();
         let cut = CutGeometry::build_from(body, g, t, prev);
+        if std::env::var("RTX_E3_MOVING_PROFILE").is_ok() {
+            eprintln!(
+                "    mask laps: cut geometry (host, within build_mask) {:.0} ms",
+                lap.elapsed().as_secs_f64() * 1e3
+            );
+        }
+        Self::from_cut(cut, g, b)
+    }
+
+    /// R6-1: the mask of a cut geometry built elsewhere (the device's
+    /// `DeviceGeom` mirror); `build_cut_from` is this after `CutGeometry::build_from`.
+    pub fn from_cut(cut: CutGeometry, g: Grid, b: Boundaries) -> Result<Self, String> {
         let (nx, ny, nz) = (g.nx, g.ny, g.nz);
         let periodic = b.z0 == Side::Periodic;
         let allowed = |side: Side| matches!(side, Side::Velocity | Side::Periodic | Side::SlipWall);