Construction mode like Fusion: with nothing selected, X (or the toolbar's Construction, or the Sketch Palette's Linetype) switches the drawing line type, so new curves are construction (or centerline) until switched back, the active mode highlighted in the palette and named in the status bar; with a selection they convert it as before; the line type is part of the drawing's undo step. Scenarios: s35 construction mode, s36 the Sketch Palette shows while sketching (also over the tools, back after a window closes, both themes) and goes with the sketch; harness shown/not_shown checks

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

crates/ui-egui/src/lib.rs

@@ -340,6 +340,10 @@ impl SolveApp {
         let t0 = now_ms();
         let r = self.session.execute(id, &params).map_err(|e| e.to_string());
         self.big_operation |= now_ms() - t0 >= recovery_ui::BIG_OPERATION_MS;
+        if let Ok(v) = &r {
+            // Curves drawn in construction (or centerline) mode take that line type.
+            sketch_palette::apply_mode(self, id, v);
+        }
         match &r {
             Ok(_) => {
                 self.session.echo(format!("{id}: done"));
@@ -416,17 +420,10 @@ impl SolveApp {
             }
         }
         // Construction toggle: selected sketch curves switch at once, otherwise pick them.
-        if id == "sketch.construction" {
-            let curves: Vec<String> = self
-                .session
-                .selection
-                .iter()
-                .filter_map(|s| if let solvecraft_engine::Sel::SketchCurve { id } = s { Some(id.clone()) } else { None })
-                .collect();
-            if !curves.is_empty() {
-                let _ = self.run(id, json!({ "curves": curves }));
-                return;
-            }
+        // Construction (X): convert the selection, or switch construction mode.
+        if id == "sketch.construction" && self.session.active_sketch.is_some() {
+            sketch_palette::toggle_construction(self);
+            return;
         }
         if let Some(spec) = solvecraft_engine::find_command(id)
             && (tools::Tool::for_command(id).is_some() || dialogs::Dialog::for_command(self, id).is_some())