Fix/Unfix on every sketch entity: points (Fix constraint) and lines, arcs, circles, ellipses, splines and conics (fixed curves hold their points and radius); ConstraintFix takes entities (fixes them all unless all are fixed); the toolbar button and the context menu act on the whole selection; fixed points never move when dragged or solved; projected geometry counts as fixed; fixed geometry is drawn green; sketch.inspect reports fixed

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

crates/engine/src/view.rs

@@ -20,6 +20,8 @@ pub mod colors {
     pub const SKETCH_DONE: Rgb = Rgb(20, 20, 20);
     pub const SKETCH_CONSTRUCTION: Rgb = Rgb(230, 130, 40);
     pub const SKETCH_FIXED: Rgb = Rgb(20, 20, 20);
+    /// Fixed (locked) geometry.
+    pub const SKETCH_LOCKED: Rgb = Rgb(0, 140, 60);
     pub const SKETCH_CENTERLINE: Rgb = Rgb(200, 110, 60);
     /// Linked (projected) reference geometry.
     pub const SKETCH_PROJECTED: Rgb = Rgb(150, 60, 190);
@@ -72,6 +74,8 @@ pub fn sketch_lines(sk: &Sketch, plane: &Plane, active: bool, determined: &[bool
     for (i, c) in sk.curves.iter().enumerate() {
         let col = if c.link.is_some() && !sk.is_text_curve(i) {
             if sk.is_lost_curve(i) { colors::SKETCH_LOST } else { colors::SKETCH_PROJECTED }
+        } else if c.fixed {
+            colors::SKETCH_LOCKED
         } else if c.centerline {
             colors::SKETCH_CENTERLINE
         } else if c.construction {