refactor(wire): add WireModel.points_low parallel buffer (empty default)

Foundation for double-single positions: WireModel now carries an
index-paired f32 residual buffer (`points_low`) next to the existing
`points` high half. Empty means "all-zero residual", so every existing
constructor (interactive draw, previews) is unchanged in behaviour;
tessellation from CAD f64 will fill it in the next steps so vertex
precision survives at UTM-scale coordinates.

Co-Authored-By: Claude Opus 4.7 <[email protected]>

src/modules/draw/draw/attdef.rs

@@ -168,6 +168,7 @@ impl CadCommand for AttdefCommand {
                 [pt.x, pt.y, pt.z - d],
                 [pt.x, pt.y, pt.z + d],
             ],
+            points_low: Vec::new(),
             color: WireModel::CYAN,
             selected: false,
             pattern_length: 0.0,

src/modules/draw/draw/ellipse.rs

@@ -613,6 +613,7 @@ fn line_wire(from: Vec3, to: Vec3) -> WireModel {
     WireModel {
         name: "rubber_band".into(),
         points: vec![[from.x, from.y, from.z], [to.x, to.y, to.z]],
+        points_low: Vec::new(),
         color: WireModel::CYAN,
         selected: false,
         pattern_length: 0.0,

src/modules/draw/draw/line.rs

@@ -78,6 +78,7 @@ impl CadCommand for LineCommand {
         Some(WireModel {
             name: "rubber_band".to_string(),
             points: vec![[last.x, last.y, last.z], [pt.x, pt.y, pt.z]],
+            points_low: Vec::new(),
             color: WireModel::CYAN,
             selected: false,
             pattern_length: 0.0,

src/modules/draw/draw/mline.rs

@@ -133,6 +133,7 @@ impl CadCommand for MlineCommand {
         Some(WireModel {
             name: "mline_preview".into(),
             points: pts,
+            points_low: Vec::new(),
             color: WireModel::CYAN,
             selected: false,
             pattern_length: 0.0,

src/modules/draw/draw/raster_image.rs

@@ -110,6 +110,7 @@ impl CadCommand for ImageCommand {
         Some(WireModel {
             name: "image_preview".into(),
             points: vec![p0, p1, p2, p3, p0],
+            points_low: Vec::new(),
             color: WireModel::CYAN,
             selected: false,
             pattern_length: 0.0,

src/modules/draw/draw/ray.rs

@@ -76,6 +76,7 @@ impl CadCommand for RayCommand {
         Some(WireModel {
             name: "ray_preview".into(),
             points: vec![[base.x, base.y, base.z], [far.x, far.y, far.z]],
+            points_low: Vec::new(),
             color: WireModel::CYAN,
             selected: false,
             pattern_length: 0.0,
@@ -157,6 +158,7 @@ impl CadCommand for XLineCommand {
                 [far_neg.x, far_neg.y, far_neg.z],
                 [far_pos.x, far_pos.y, far_pos.z],
             ],
+            points_low: Vec::new(),
             color: WireModel::CYAN,
             selected: false,
             pattern_length: 0.0,

src/modules/draw/draw/revcloud.rs

@@ -82,6 +82,7 @@ impl CadCommand for RevCloudCommand {
         Some(WireModel {
             name: "revcloud_preview".into(),
             points: preview_pts,
+            points_low: Vec::new(),
             color: WireModel::CYAN,
             selected: false,
             pattern_length: 0.0,

src/modules/draw/draw/wipeout.rs

@@ -122,6 +122,7 @@ impl CadCommand for WipeoutCommand {
                         [min.x, max.y, max.z],
                         [min.x, min.y, min.z],
                     ],
+                    points_low: Vec::new(),
                     color: WireModel::CYAN,
                     selected: false,
                     pattern_length: 0.0,
@@ -148,6 +149,7 @@ impl CadCommand for WipeoutCommand {
                 Some(WireModel {
                     name: "wipeout_poly_preview".into(),
                     points: pts,
+                    points_low: Vec::new(),
                     color: WireModel::CYAN,
                     selected: false,
                     pattern_length: 0.0,

src/modules/draw/inquiry/area.rs

@@ -66,6 +66,7 @@ impl CadCommand for AreaCommand {
         Some(WireModel {
             name: "area_preview".into(),
             points: pts,
+            points_low: Vec::new(),
             color: WireModel::CYAN,
             selected: false,
             pattern_length: 0.0,

src/modules/draw/inquiry/dist.rs

@@ -61,6 +61,7 @@ impl CadCommand for DistCommand {
         Some(WireModel {
             name: "dist_preview".into(),
             points: vec![[p1.x, p1.y, p1.z], [pt.x, pt.y, pt.z]],
+            points_low: Vec::new(),
             color: WireModel::CYAN,
             selected: false,
             pattern_length: 0.0,