feat(polyline): smooth per-segment taper for varying-width wide polylines

A wide polyline with per-vertex varying widths rendered at its widest edge
(uniform-width ones were already exact). Draw the true taper instead.

`WireModel.taper_widths` carries a per-point full band width. The wire
instance (native slim + web fat) gains per-endpoint `world_hw_a/b`, and both
wire shaders interpolate `mix(hw_a, hw_b, which_end)` so each segment's band
narrows/widens linearly — depth-tested, and the linetype dash still applies.

Alignment (widths must match the tessellated points) is solved by building
both together: a new `TruckObject::TaperedLines(points, widths)`, filled by
`common::tapered_band_points` (straight = endpoints, arc = 16 samples with the
width lerped along it). to_truck routes a varying-width polyline here —
LwPolyline before the PLINEGEN split, Polyline2D at its return — while a
uniform-width one keeps the constant-band Contour path unchanged. `world_width`
stays the widest edge as the PDF-stroke + zoom-floor fallback.

Blocks fall back to the constant-widest band (`LocalWire` carries no
taper_widths).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/modules/annotate/aligned_dim.rs

@@ -186,6 +186,7 @@ impl CadCommand for AlignedDimensionCommand {
         let p1 = p1.as_vec3();
         let p2 = p2.as_vec3();
         Some(WireModel {
+            taper_widths: Vec::new(),
             world_width: 0.0,
             fill_is_3d: false,
             pick_tris: Vec::new(),
@@ -238,6 +239,7 @@ fn preview_aligned(p1: DVec3, p2: DVec3, dim_pt: DVec3) -> WireModel {
     let d1 = d1.as_vec3();
     let d2 = d2.as_vec3();
     WireModel {
+        taper_widths: Vec::new(),
         world_width: 0.0,
         fill_is_3d: false,
         pick_tris: Vec::new(),

src/modules/annotate/angular_dim.rs

@@ -130,6 +130,7 @@ fn v3(pt: DVec3) -> Vector3 {
 
 fn preview_wire(points: Vec<Vec3>) -> WireModel {
     WireModel {
+        taper_widths: Vec::new(),
         world_width: 0.0,
         fill_is_3d: false,
         pick_tris: Vec::new(),

src/modules/annotate/diameter_dim.rs

@@ -180,6 +180,7 @@ fn v3(p: DVec3) -> Vector3 {
 
 fn preview_line(a: Vec3, b: Vec3) -> WireModel {
     WireModel {
+        taper_widths: Vec::new(),
         world_width: 0.0,
         fill_is_3d: false,
         pick_tris: Vec::new(),

src/modules/annotate/dim_baseline.rs

@@ -179,6 +179,7 @@ impl CadCommand for DimBaselineCommand {
         let dim_line_pt2 = dim_line_pt2.as_vec3();
         let pt = pt.as_vec3();
         Some(WireModel {
+            taper_widths: Vec::new(),
             world_width: 0.0,
             fill_is_3d: false,
             pick_tris: Vec::new(),

src/modules/annotate/dim_continue.rs

@@ -159,6 +159,7 @@ impl CadCommand for DimContinueCommand {
         let dim_line_pt = p1 + perp * (dim_line_perp - p1.dot(perp));
         let dim_line_pt2 = pt + perp * (dim_line_perp - pt.dot(perp));
         Some(WireModel {
+            taper_widths: Vec::new(),
             world_width: 0.0,
             fill_is_3d: false,
             pick_tris: Vec::new(),

src/modules/annotate/dimjogline.rs

@@ -85,6 +85,7 @@ impl CadCommand for DimJogLineCommand {
         }
         let d = 0.3_f32;
         Some(WireModel {
+            taper_widths: Vec::new(),
             world_width: 0.0,
             fill_is_3d: false,
             pick_tris: Vec::new(),

src/modules/annotate/dimtedit.rs

@@ -100,6 +100,7 @@ impl CadCommand for DimTeditCommand {
         }
         let d = 0.2_f32;
         Some(WireModel {
+            taper_widths: Vec::new(),
             world_width: 0.0,
             fill_is_3d: false,
             pick_tris: Vec::new(),

src/modules/annotate/leader_cmd.rs

@@ -163,6 +163,7 @@ fn preview_wire(pts: &[Vec3]) -> WireModel {
         points.push([w2.x, w2.y, w2.z]);
     }
     WireModel {
+        taper_widths: Vec::new(),
         world_width: 0.0,
         fill_is_3d: false,
         pick_tris: Vec::new(),

src/modules/annotate/linear_dim.rs

@@ -218,6 +218,7 @@ fn v3(pt: DVec3) -> Vector3 {
 
 fn preview_wire(points: Vec<DVec3>) -> WireModel {
     WireModel {
+        taper_widths: Vec::new(),
         world_width: 0.0,
         fill_is_3d: false,
         pick_tris: Vec::new(),

src/modules/annotate/mleader_cmd.rs

@@ -150,6 +150,7 @@ fn preview_wire(pts: &[Vec3]) -> WireModel {
         points.push([w2.x, w2.y, w2.z]);
     }
     WireModel {
+        taper_widths: Vec::new(),
         world_width: 0.0,
         fill_is_3d: false,
         pick_tris: Vec::new(),

src/modules/annotate/mleader_edit.rs

@@ -458,6 +458,7 @@ impl CadCommand for MLeaderCollectCommand {
 
 fn preview_wire(pts: &[Vec3]) -> WireModel {
     WireModel {
+        taper_widths: Vec::new(),
         world_width: 0.0,
         fill_is_3d: false,
         pick_tris: Vec::new(),

src/modules/annotate/ordinate_dim.rs

@@ -121,6 +121,7 @@ fn ordinate_elbow(feature: DVec3, leader: DVec3, is_x: bool) -> DVec3 {
 
 fn preview_wire(points: Vec<Vec3>) -> WireModel {
     WireModel {
+        taper_widths: Vec::new(),
         world_width: 0.0,
         fill_is_3d: false,
         pick_tris: Vec::new(),

src/modules/annotate/qdim.rs

@@ -90,6 +90,7 @@ impl CadCommand for QdimCommand {
         }
         let d = 0.5_f32;
         Some(WireModel {
+            taper_widths: Vec::new(),
             world_width: 0.0,
             fill_is_3d: false,
             pick_tris: Vec::new(),

src/modules/annotate/radius_dim.rs

@@ -185,6 +185,7 @@ fn v3(pt: DVec3) -> Vector3 {
 
 fn preview_wire(points: Vec<Vec3>) -> WireModel {
     WireModel {
+        taper_widths: Vec::new(),
         world_width: 0.0,
         fill_is_3d: false,
         pick_tris: Vec::new(),

src/modules/annotate/table_cmd.rs

@@ -139,6 +139,7 @@ impl CadCommand for TableCommand {
             let y = pt.y;
             let z = pt.z;
             Some(WireModel {
+                taper_widths: Vec::new(),
                 world_width: 0.0,
                 fill_is_3d: false,
                 pick_tris: Vec::new(),

src/modules/annotate/tolerance_cmd.rs

@@ -84,6 +84,7 @@ impl CadCommand for ToleranceCommand {
         }
         let d = 0.15_f32;
         Some(WireModel {
+            taper_widths: Vec::new(),
             world_width: 0.0,
             fill_is_3d: false,
             pick_tris: Vec::new(),