Sketch drawing: clicking a model vertex projects it into the sketch (linked point) and draws from it, as Fusion does ("vertex:x,y,z" point arguments)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AS5Tn3xieewUSg3uxrMVdL

crates/ui-egui/src/sketch_tools.rs

@@ -40,6 +40,13 @@ pub fn refine_snap(
     let (a, b) = (proj.to_screen(plane.to_world(lp))?, proj.to_screen(plane.to_world(lp + Vec2::X))?);
     let px = 1.0 / (a.distance(b) as f64).max(1e-9);
     let tol = 7.0 * px;
+    // A model vertex under the cursor: drawing on it projects it into the sketch.
+    for h in pick(app, proj, a) {
+        if let Hit::Vertex { point, .. } = h {
+            SNAP.with(|s| *s.borrow_mut() = Some(("Pt", plane.to_local(point))));
+            return Some((plane.to_local(point), Some(format!("vertex:{},{},{}", point.x, point.y, point.z))));
+        }
+    }
     let mut best: Option<(f64, &'static str, Vec2)> = None;
     let mut mid_of: Option<String> = None;
     for (i, c) in sk.curves.iter().enumerate() {