Fix live extrusion surface grip editing

src/app/update/viewport.rs

@@ -1535,15 +1535,30 @@ impl OpenCADStudio {
             }
 
             if let Some(axis) = grip.axis {
-                snapped = cursor_on_projected_axis(
-                    p,
-                    bounds,
-                    view_rot,
-                    eye,
-                    grip.origin_world,
-                    axis,
-                )
-                .unwrap_or(snapped);
+                let acquired_point = otrack_hit.is_some()
+                    || snap_hit.is_some_and(|hit| {
+                        hit.snap_type != crate::snap::SnapType::Grid
+                    });
+                if acquired_point {
+                    if let Some(axis) = axis.try_normalize() {
+                        // An axis grip still moves on its construction axis, but
+                        // an acquired object point supplies the exact coordinate
+                        // along that axis. This lets height and draft arrows seat
+                        // back onto existing surface/solid geometry.
+                        snapped = grip.origin_world
+                            + axis * (snapped - grip.origin_world).dot(axis);
+                    }
+                } else {
+                    snapped = cursor_on_projected_axis(
+                        p,
+                        bounds,
+                        view_rot,
+                        eye,
+                        grip.origin_world,
+                        axis,
+                    )
+                    .unwrap_or(snapped);
+                }
             }
 
             let snap_ms = snap_started.elapsed().as_secs_f64() * 1000.0;
@@ -1751,6 +1766,26 @@ impl OpenCADStudio {
             let preview_ms = preview_started.elapsed().as_secs_f64() * 1000.0;
             let geometry_ms = grip_started.elapsed().as_secs_f64() * 1000.0;
             self.refresh_selected_grips();
+            // A history rebuild can clamp a requested value or move a derived
+            // construction handle non-linearly. Rebase each active target onto
+            // the freshly rebuilt grip so the hot arrow remains attached to the
+            // live surface and reverses immediately from a geometric limit.
+            let refreshed_targets: Vec<_> = self.tabs[i]
+                .selected_grip_handles
+                .iter()
+                .copied()
+                .zip(self.tabs[i].selected_grips.iter())
+                .map(|(handle, grip)| ((handle, grip.id), grip.world))
+                .collect();
+            if let Some(active) = self.tabs[i].active_grip.as_mut() {
+                for target in &mut active.targets {
+                    if let Some((_, world)) = refreshed_targets.iter().find(|((handle, id), _)| {
+                        *handle == target.handle && *id == target.grip_id
+                    }) {
+                        target.last_world = *world;
+                    }
+                }
+            }
             let grips_ms = grip_started.elapsed().as_secs_f64() * 1000.0 - geometry_ms;
             // Properties are refreshed when the grip is committed or cancelled.
             // Rebuilding the inspector on every pointer event adds no drawing