STEP: open/insert/drag-drop

Import base feature (FeatureKind::Import, timeline type BaseFeature) holding
the STEP text and the file's product tree; bodies named from the file.
doc.open accepts .step/.stp (any case) as a new design; Insert STEP
(FusionImportCommandFromToolbar) adds one to the current design; File menu,
SOLID > INSERT, drag-and-drop (insert into a non-empty design, else open),
'solvecraft part.step', MCP open. Features (fillet, hole, sketch-on-face
cut, shell) work on imported bodies. Imports are cached so a file is read
once per command. Measure tightens its chord tolerance for small radii.

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

crates/ui-egui/src/icons.rs

@@ -361,6 +361,10 @@ pub fn paint(p: &Painter, r: Rect, name: &str, ink: Color32, fill: Color32, acce
             pen.poly(&[(4.0, 10.0), (4.0, 20.0), (16.0, 20.0), (16.0, 10.0)], pen.fill, ink);
             pen.arrow((10.0, 14.0), (20.0, 4.0), a);
         }
+        "import" => {
+            pen.iso_box(4.0, 12.0, 12.0, 7.0, 7.0);
+            pen.arrow((20.0, 3.0), (12.0, 11.0), a);
+        }
         "home" => {
             pen.poly(&[(4.0, 12.0), (12.0, 4.0), (20.0, 12.0)], pen.fill, ink);
             pen.poly(&[(6.0, 12.0), (18.0, 12.0), (18.0, 20.0), (6.0, 20.0)], pen.fill, ink);

crates/ui-egui/src/lib.rs

@@ -166,6 +166,12 @@ impl SolveApp {
     /// that have them, otherwise run it with defaults.
     pub fn start(&mut self, id: &str) {
         self.tool = None;
+        if id == "FusionImportCommandFromToolbar" {
+            if let Some(p) = self.services.pick_open.as_ref().and_then(|f| f()) {
+                self.insert_path(&p);
+            }
+            return;
+        }
         if id == "SketchStop" {
             let r = self.run(id, json!({}));
             if r.is_ok()
@@ -240,6 +246,25 @@ impl SolveApp {
         }
     }
 
+    /// Insert a STEP file's bodies into the current design (an Import base feature).
+    pub fn insert_path(&mut self, path: &str) {
+        if let Ok(r) = self.run("FusionImportCommandFromToolbar", json!({ "path": path })) {
+            self.fit_view();
+            if let Some(w) = r["warnings"].as_array().filter(|w| !w.is_empty()) {
+                self.set_status(format!("imported with {} warning(s): {}", w.len(), w.first().and_then(Value::as_str).unwrap_or("")), false);
+            }
+        }
+    }
+
+    /// A dropped file: a STEP file joins a design that has features, anything else opens.
+    pub fn drop_path(&mut self, path: &str) {
+        if solvecraft_engine::io::is_step_path(path) && !self.session.doc.features.is_empty() {
+            self.insert_path(path);
+        } else {
+            self.open_path(path);
+        }
+    }
+
     /// Frame the model at once (programmatic use; the toolbar animates).
     pub fn fit_view(&mut self) {
         self.cam_anim = None;
@@ -321,7 +346,7 @@ impl SolveApp {
         for f in ctx.input(|i| i.raw.dropped_files.clone()) {
             let p = f.path().to_string_lossy().to_string();
             if !p.is_empty() {
-                self.open_path(&p);
+                self.drop_path(&p);
             }
         }
     }

crates/ui-egui/src/timeline.rs

@@ -30,6 +30,7 @@ fn icon_of(k: &FeatureKind) -> &'static str {
         FeatureKind::Draft { .. } => "draft",
         FeatureKind::Split { .. } => "split",
         FeatureKind::Move { .. } => "move",
+        FeatureKind::Import { .. } => "import",
     }
 }
 

crates/ui-egui/src/toolbar.rs

@@ -127,6 +127,10 @@ fn file_menu(app: &mut SolveApp, ctx: &egui::Context) {
                 }
                 close = true;
             }
+            if item(ui, "Insert STEP…", "") {
+                app.start("FusionImportCommandFromToolbar");
+                close = true;
+            }
             if item(ui, "Save", "Ctrl+S") {
                 save(app);
                 close = true;