refactor: finish OST f64 integration; drop vestigial _f64 suffixes

- Object-snap-tracking points now project through the relative-to-eye path
  (view_proj_rte + eye) instead of the full view-projection, so they stay
  precise at UTM-scale coordinates — the last consumer of the legacy full
  view_proj outside the CPU frustum-cull / scissor path.
- Rename Camera::project_f64 → project and unproject_on_plane_f64 →
  unproject_on_plane: the f32 twins are gone, so the disambiguating suffix
  is vestigial. eye_f64 keeps its name — the f32 eye() still builds the
  view matrices.
- Remove stale #[allow(dead_code)] from eye_f64 / project / unproject_on_plane
  (all live now).

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

src/app/view.rs

@@ -221,14 +221,19 @@ impl OpenCADStudio {
                 None
             };
 
-            // OST tracking points → screen positions.
+            // OST tracking points → screen positions, projected relative-to-eye
+            // so they stay precise at UTM-scale coordinates (the full
+            // view-projection cancels catastrophically in f32).
             let ost_points: Vec<overlay::OstTrackPoint> = if self.snapper.otrack_enabled {
-                let vp_mat = tab.scene.camera.borrow().view_proj(vp_bounds);
+                let (view_rot, eye) = {
+                    let cam = tab.scene.camera.borrow();
+                    (cam.view_proj_rte(vp_bounds), cam.eye_f64())
+                };
                 self.snapper
                     .tracking_points
                     .iter()
                     .map(|&wp| {
-                        let ndc = vp_mat.project_point3(wp);
+                        let ndc = view_rot.project_point3((wp.as_dvec3() - eye).as_vec3());
                         overlay::OstTrackPoint {
                             screen: iced::Point::new(
                                 (ndc.x + 1.0) * 0.5 * vp_bounds.width,

src/scene/pick/grip.rs

@@ -43,7 +43,7 @@ pub fn grips_to_screen(
             // Project from the f64 grip position via the relative-to-eye path so
             // the grip stays glued to the wire at UTM-scale coordinates (an
             // `as_vec3` cast first would quantize it ~0.5 m off at high zoom).
-            let screen = match camera.project_f64(g.world, bounds) {
+            let screen = match camera.project(g.world, bounds) {
                 Some(p) => Point::new(bounds.x + p.x, bounds.y + p.y),
                 None => Point::new(f32::NAN, f32::NAN),
             };
@@ -115,7 +115,7 @@ pub fn find_hit_grip(
     let mut best: Option<(usize, bool, DVec3)> = None;
 
     for g in grips {
-        let Some(screen) = camera.project_f64(g.world, bounds) else {
+        let Some(screen) = camera.project(g.world, bounds) else {
             continue;
         };
         let screen = Point::new(screen.x, screen.y);
@@ -131,7 +131,7 @@ pub fn find_hit_grip(
 }
 
 /// Project an f64 world point with an explicit relative-to-eye `(view_rot,
-/// eye)` pair — the camera-less form of `Camera::project_f64`. Used by the
+/// eye)` pair — the camera-less form of `Camera::project`. Used by the
 /// in-viewport editing path, which supplies a *composed* model→screen view
 /// (see `Scene::composed_viewport_view`) instead of a real camera.
 fn project_rte(world: DVec3, view_rot: Mat4, eye: DVec3, bounds: Rectangle) -> Option<Vec2> {

src/scene/view/camera.rs

@@ -79,7 +79,6 @@ impl Camera {
     /// Eye position in full f64 precision (offset-relative world space). Used
     /// by the relative-to-eye render path; the f32 [`eye`] stays for ray/pick
     /// math that operates at human scale.
-    #[allow(dead_code)] // consumed by the relative-to-eye uniform (next phase)
     pub fn eye_f64(&self) -> DVec3 {
         let eye_dir = (self.rotation * Vec3::Z).as_dvec3();
         self.target + eye_dir * self.distance as f64
@@ -160,8 +159,7 @@ impl Camera {
     /// the rotation-only projection, so it stays exact at large absolute
     /// coordinates — the CPU equivalent of the GPU's relative-to-eye path.
     /// Returns `None` for points at/behind the eye plane (w ≈ 0).
-    #[allow(dead_code)] // consumed by the world_offset-removal CPU migration
+    pub fn project(&self, p: glam::DVec3, bounds: Rectangle) -> Option<glam::Vec2> {
-    pub fn project_f64(&self, p: glam::DVec3, bounds: Rectangle) -> Option<glam::Vec2> {
         let rel = (p - self.eye_f64()).as_vec3();
         let clip = self.view_proj_rte(bounds) * rel.extend(1.0);
         if clip.w.abs() < 1e-9 {
@@ -178,8 +176,7 @@ impl Camera {
     /// is built in eye-relative space (precise), intersected with the plane
     /// expressed relative to the eye, then shifted back by the f64 eye — so the
     /// returned world point keeps full precision at large absolute coordinates.
-    #[allow(dead_code)] // consumed by the world_offset-removal CPU migration
+    pub fn unproject_on_plane(
-    pub fn unproject_on_plane_f64(
         &self,
         screen: Point,
         bounds: Rectangle,
@@ -242,13 +239,13 @@ impl Camera {
         plane_normal: Vec3,
         plane_point: glam::DVec3,
     ) -> glam::DVec3 {
-        self.unproject_on_plane_f64(screen, bounds, plane_normal, plane_point)
+        self.unproject_on_plane(screen, bounds, plane_normal, plane_point)
     }
 
     /// Project a screen point onto the plane through the orbit target.
     pub fn pick_on_target_plane(&self, screen: Point, bounds: Rectangle) -> glam::DVec3 {
         let forward = (self.target.as_vec3() - self.eye()).normalize_or(Vec3::NEG_Z);
-        self.unproject_on_plane_f64(screen, bounds, forward, self.target)
+        self.unproject_on_plane(screen, bounds, forward, self.target)
     }