Combine: a cut keeps a body joined from separate pieces in one body (#2247)

Thanks @H1D.

crates/engine/src/cmd/features.rs

@@ -547,10 +547,11 @@ fn add_feature_in(s: &mut Session, p: &Value, kind: FeatureKind, world: bool) ->
     }
     let st = s.model.state();
     let bodies: Vec<&str> = st.bodies.iter().map(|b| b.name.as_str()).collect();
-    // The bodies this feature made, apart from the ones it changed or that were there (#374).
-    let created: Vec<&str> = st.bodies.iter().filter(|b| b.feature == id).map(|b| b.name.as_str()).collect();
     // Bodies that were there before and now have other geometry, and bodies that are gone.
     let old: std::collections::HashMap<&str, &solidcraft_doc::kernel::Body> = before.bodies.iter().map(|b| (b.name.as_str(), &b.body)).collect();
+    // The bodies this feature made, apart from the ones it changed or that were there (#374),
+    // and the pieces a cut left of a body made earlier, which keep that body's feature.
+    let created: Vec<&str> = st.bodies.iter().filter(|b| b.feature == id || !old.contains_key(b.name.as_str())).map(|b| b.name.as_str()).collect();
     let now: std::collections::HashSet<&str> = st.bodies.iter().map(|b| b.name.as_str()).collect();
     let changed: Vec<&str> =
         st.bodies.iter().filter(|b| b.feature != id && old.get(b.name.as_str()).is_some_and(|o| !o.same(&b.body))).map(|b| b.name.as_str()).collect();