M0: workspace, geometry foundation, sketch constraint solver, kernel boundary

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/kernel/src/step.rs

@@ -0,0 +1,18 @@
+use monstertruck_io::step::save;
+
+use crate::body::Body;
+use crate::{KernelError, Result, guard};
+
+/// STEP (ISO 10303-21, AP203-style geometry) text for the given bodies.
+pub fn step_export(bodies: &[&Body], system: &str) -> Result<String> {
+    if bodies.is_empty() {
+        return Err(KernelError::Invalid("nothing to export".into()));
+    }
+    guard("step export", || {
+        let cs: Vec<_> = bodies.iter().map(|b| b.solid.compress()).collect();
+        let models = save::StepModels::from_iter(cs.iter());
+        let header = save::StepHeaderDescriptor { organization_system: system.to_owned(), ..Default::default() };
+        let out = save::CompleteStepDisplay::new(models, header).to_string();
+        Ok(out)
+    })
+}