feat(dynamic-input): per-step specs for rectangle, polygon and ellipse

Extend the DynSpec coverage and add the guides those commands need:

- Rectangle: two-corner enters width/height as unsigned magnitudes (the
  sign follows the cursor side, like the angle entry), drawn with the
  rectangle as the guide; rotated rectangle's height is a single distance
  measured square to the base edge (dimension line offset off the edge
  with extension lines); centre rectangle shows half-width/half-height.
- Polygon: inscribed/circumscribed vertex step shows radius + rotation.
- Ellipse: minor-axis step (all three modes) measures the half-length
  perpendicular to the major axis and draws that semi-axis from the
  centre; angle steps anchor their arc at the centre.

Adds DynGuide::Perp / PerpDim (perpendicular measure to a reference line)
and DynSpec::ref_point, plus Width/Height role handling (unsigned display,
cursor-signed commit) and diameter value scaling.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

src/command/mod.rs

@@ -278,7 +278,8 @@ pub enum DynRole {
     Height,
     /// Typed-only scale factor.
     Factor,
-    /// Typed-only integer count.
+    /// Typed-only integer count. Reserved for upcoming command migrations.
+    #[allow(dead_code)]
     Count,
 }
 
@@ -321,12 +322,21 @@ pub enum DynGuide {
     Radius,
     /// The two rectangle sides (width × height) from the anchor corner.
     RectSides,
+    /// A line from the anchor, perpendicular to the reference line (anchor →
+    /// `DynSpec::ref_point`), reaching the cursor's perpendicular offset — the
+    /// measured semi-axis (ellipse minor). The value is that offset.
+    Perp,
+    /// Like `Perp` but drawn as a dimension: the measured segment is offset off
+    /// the edge with extension lines back to its endpoints (rectangle height).
+    PerpDim,
 }
 
 /// Where a step's values are measured from.
 #[derive(Clone, Copy, PartialEq, Debug)]
 pub enum DynAnchor {
-    /// The previous committed point (`App::last_point`).
+    /// The previous committed point (`App::last_point`). Reserved — current
+    /// specs pass the anchor explicitly via `Point`.
+    #[allow(dead_code)]
     LastPoint,
     /// An explicit world point.
     Point(Vec3),
@@ -352,6 +362,9 @@ pub struct DynSpec {
     pub anchor: DynAnchor,
     pub fields: Vec<DynFieldSpec>,
     pub guide: DynGuide,
+    /// Far end of a reference line through `anchor` (only used by
+    /// [`DynGuide::Perp`]); `None` otherwise.
+    pub ref_point: Option<Vec3>,
 }
 
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