refactor: drop truck, and evaluate every curve through the kernel

The last four truck crates are gone from the manifest. What they were doing
falls into three parts, and each now has one answer instead of two.

NURBS evaluation. truck was carrying B-spline curves and surfaces for the
SPLINE entity, hatch boundaries, BLEND's endpoint frames, the spline preview
and ACIS spline-surface faces. The kernel now has both, over one de Boor
written across however many coordinates a control point holds — so a plane
curve and a space curve cannot drift apart, and a surface is the same
algorithm applied twice. The rational and the polynomial cases stop being
separate types: weights absent means polynomial.

The entity conversion. Every LINE, ARC, ELLIPSE, SPLINE and polyline was
built into truck topology purely so it could be sampled back into points.
They are sampled through `entities::curve` now, which is where each one's
geometry is already defined once and what EXTRUDE and REVOLVE read — so a
circle drawn on screen and a circle handed to the Model tab come from the
same definition. That retires four of TruckObject's variants and the module
is renamed for what it does.

SWEEP and LOFT. Both only ever produced a mesh, so both are built from point
lists: a band of quads per span, and a lid where a profile closes. Lofting
profiles of different densities resamples them by distance rather than by
index, so a circle lofted to a square no longer twists.

Two things worth noting for anyone reading the old comments. The tolerance
globals that lived in the tessellation module were never about truck at all —
they are the per-frame chord height, and they move to `curve_tol`. And the
rule that a profile handed over as `Lines` silently broke EXTRUDE and REVOLVE
no longer holds: those read the curve directly and never look at this channel.

The two `automation` test failures are unchanged from before this and are not
caused by it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/entities/ellipse.rs

@@ -1,5 +1,4 @@
 use acadrust::entities::Ellipse;
-use truck_modeling::{builder, BSplineCurve, Curve, Edge, KnotVec, Point3, Wire};
 
 use crate::entities::curve::CurveSnap;
 use crate::t;
@@ -8,11 +7,11 @@ use crate::command::EntityTransform;
 use crate::entities::common::{
     center_grip, edit_prop as edit, parse_f64, ro_prop as ro, square_grip,
 };
-use crate::entities::traits::TruckConvertible;
-use crate::scene::convert::acad_to_truck::{TruckEntity, TruckObject};
+use crate::entities::traits::RenderConvertible;
+use crate::scene::convert::acad_to_render::{RenderEntity, RenderObject};
 use crate::scene::model::object::{GripApply, GripDef, PropSection};
 
-fn to_truck(ell: &Ellipse) -> TruckEntity {
+fn to_render(ell: &Ellipse) -> RenderEntity {
     // ELLIPSE is one of the few WCS entities in DXF: `center` (code 10) and
     // `major_axis` (code 11) are world coordinates already — unlike ARC /
     // CIRCLE, whose centers are OCS. The converter knows that; this used to
@@ -35,9 +34,9 @@ fn to_truck(ell: &Ellipse) -> TruckEntity {
     // SWEEP read their profile out of `Contour` / `Curve` and have no arm for
     // a bare point list, so an ellipse handed over as `Lines` would stop
     // being usable as either.
-    let empty = |snap: CurveSnap| TruckEntity {
+    let empty = |snap: CurveSnap| RenderEntity {
         pick_tris: Vec::new(),
-        object: TruckObject::Lines(Vec::new()),
+        object: RenderObject::Lines(Vec::new()),
         snap_pts: snap.snap_pts,
         tangent_geoms: vec![],
         key_vertices: vec![],
@@ -46,42 +45,14 @@ fn to_truck(ell: &Ellipse) -> TruckEntity {
     let Some(planar) = curve else {
         return empty(snap);
     };
-    let points: Vec<Point3> = crate::entities::curve::curve_points(&planar)
-        .into_iter()
-        .map(|p| Point3::new(p[0], p[1], p[2]))
-        .collect();
+    let points = crate::entities::curve::curve_points(&planar);
     if points.len() < 2 {
         return empty(snap);
     }
 
-    // Closure decided on the points rather than on the stored parameters. A
-    // file that writes an end parameter a hair short of a full turn still
-    // draws a closed ellipse, and an open edge whose two vertices sit on top
-    // of each other is not something a plane can be attached to.
-    let ends_meet = {
-        let (first, last) = (points[0], *points.last().expect("checked non-empty"));
-        let span = first.x.abs().max(first.y.abs()).max(first.z.abs()).max(1.0);
-        let gap = first - last;
-        (gap.x * gap.x + gap.y * gap.y + gap.z * gap.z).sqrt() <= 1e-9 * span
-    };
-    let object = if planar.is_closed() || ends_meet {
-        // Two half-edges rather than one closed edge: a single edge whose
-        // two vertices coincide is not a wire truck will attach a plane to.
-        let split = points.len() / 2;
-        let upper = points[..=split].to_vec();
-        let lower = points[split..].to_vec();
-        let v_pos = builder::vertex(points[0]);
-        let v_neg = builder::vertex(points[split]);
-        let edge_upper = Edge::new(&v_pos, &v_neg, polyline_curve(upper));
-        let edge_lower = Edge::new(&v_neg, &v_pos, polyline_curve(lower));
-        TruckObject::Contour([edge_upper, edge_lower].into_iter().collect::<Wire>())
-    } else {
-        let v_start = builder::vertex(points[0]);
-        let v_end = builder::vertex(*points.last().expect("checked non-empty"));
-        TruckObject::Curve(Edge::new(&v_start, &v_end, polyline_curve(points)))
-    };
+    let object = RenderObject::Lines(points);
 
-    TruckEntity {
+    RenderEntity {
         pick_tris: Vec::new(),
         object,
         snap_pts: snap.snap_pts,
@@ -91,15 +62,11 @@ fn to_truck(ell: &Ellipse) -> TruckEntity {
     }
 }
 
-/// A truck curve that passes through every one of `points` in order.
+/// A curve through every one of `points` in order.
 ///
 /// Degree one, so the control polygon *is* the curve — the same thing the
 /// hand-built sampling produced, without restating how a B-spline is put
 /// together at each site.
-fn polyline_curve(points: Vec<Point3>) -> Curve {
-    let spans = points.len().saturating_sub(1);
-    Curve::BSplineCurve(BSplineCurve::new(KnotVec::uniform_knot(1, spans), points))
-}
 
 fn grips(ell: &Ellipse) -> Vec<GripDef> {
     let ctr = glam::DVec3::new(ell.center.x, ell.center.y, ell.center.z);
@@ -302,9 +269,9 @@ fn apply_transform(ell: &mut Ellipse, t: &EntityTransform) {
     });
 }
 
-impl TruckConvertible for Ellipse {
-    fn to_truck(&self, _document: &acadrust::CadDocument) -> Option<TruckEntity> {
-        Some(to_truck(self))
+impl RenderConvertible for Ellipse {
+    fn to_render(&self, _document: &acadrust::CadDocument) -> Option<RenderEntity> {
+        Some(to_render(self))
     }
 }