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/doc/src/document.rs

@@ -280,6 +280,17 @@ pub enum FeatureKind {
         #[serde(default, skip_serializing_if = "Option::is_none")]
         angle: Option<String>,
     },
+    /// A non-parametric base feature: bodies imported from a STEP file. The STEP text is kept
+    /// in the design (it is the B-rep), so the design reopens without the original file.
+    Import {
+        /// Source file name (display only).
+        file: String,
+        /// The STEP (ISO 10303-21) text.
+        step: String,
+        /// The file's product/assembly tree, kept for components.
+        #[serde(default, skip_serializing_if = "Vec::is_empty")]
+        components: Vec<solvecraft_kernel::StepNode>,
+    },
 }
 
 /// One loft section: profiles of a sketch.
@@ -379,6 +390,7 @@ impl FeatureKind {
             FeatureKind::Draft { .. } => "DraftFeature",
             FeatureKind::Split { .. } => "SplitBodyFeature",
             FeatureKind::Move { .. } => "MoveFeature",
+            FeatureKind::Import { .. } => "BaseFeature",
         }
     }
     /// Default name prefix (`Extrude` → `Extrude1`).
@@ -405,6 +417,7 @@ impl FeatureKind {
             FeatureKind::Draft { .. } => "Draft",
             FeatureKind::Split { .. } => "Split",
             FeatureKind::Move { .. } => "Move",
+            FeatureKind::Import { .. } => "Import",
         }
     }
     /// Every expression the feature uses.
@@ -465,6 +478,7 @@ impl FeatureKind {
                     v.push(a);
                 }
             }
+            FeatureKind::Import { .. } => {}
         }
         v
     }

crates/doc/src/eval.rs

@@ -1100,5 +1100,29 @@ fn eval_feature(doc: &Document, vals: &BTreeMap<String, Value>, f: &Feature, st:
             }
             Ok(())
         }
+        FeatureKind::Import { step, .. } => {
+            let imp = kernel::step_import_shared(step)?;
+            for (k, b) in imp.bodies.iter().enumerate() {
+                let base = f.body_names.get(k).filter(|n| !n.trim().is_empty()).unwrap_or(&b.name);
+                let name = unique_body_name(st, base);
+                st.bodies.push(ModelBody::new(name, b.body.clone(), f.id));
+            }
+            if !imp.warnings.is_empty() {
+                let n = imp.warnings.len();
+                let shown: Vec<&str> = imp.warnings.iter().take(3).map(String::as_str).collect();
+                let more = if n > 3 { format!(" (+{} more)", n - 3) } else { String::new() };
+                *warning = Some(format!("{}{more}", shown.join("; ")));
+            }
+            Ok(())
+        }
     }
 }
+
+/// `base`, or `base (2)`, `base (3)`… if a body already has that name.
+fn unique_body_name(st: &ModelState, base: &str) -> String {
+    let base = if base.trim().is_empty() { "Body" } else { base.trim() };
+    if st.body(base).is_none() {
+        return base.to_string();
+    }
+    (2..).map(|i| format!("{base} ({i})")).find(|n| st.body(n).is_none()).unwrap_or_else(|| base.to_string())
+}