test: failing regression test for #259: Join with explicit targets also merges a non-target body that the tool touches (#274)

* test: reproduce #259 (Join with explicit `targets` also merges a non-target body that the tool touches)

* Primitives honour `targets` for join/cut/intersect (#259)

solid.box/cylinder/sphere/torus had no targets field, so a `targets` list was
ignored and every body of the component took part: a join also merged a touched
non-target body, a cut also cut (or deleted) one. Their `targets` now become the
feature's participants.

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

---------

Co-authored-by: bherbruck <brennen.herbruck@gmail.com>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

crates/engine/src/cmd/features.rs

@@ -23,10 +23,10 @@ pub static COMMANDS: &[CommandSpec] = &[
         .icon("sweep")
         .params("sketch: profile sketch; profiles?; path_sketch: sketch; path: [curve ids in order]; operation?, targets?, name?, body_name?"),
     CommandSpec::new("solid.loft", "Loft", loft).at("SOLID", "CREATE").icon("loft").params("sections: [{sketch, profiles?} | {sketch, point: id} (an apex)] (2 or more, in order); operation?, targets?, name?, body_name?"),
-    CommandSpec::new("solid.box", "Box", prim_box).at("SOLID", "CREATE").icon("box").params("length, width, height: expr; corner?: [x,y,z] | center?: [x,y,z] (numbers in mm or length expressions; default: the origin); operation?, name?, body_name?"),
-    CommandSpec::new("solid.cylinder", "Cylinder", prim_cylinder).at("SOLID", "CREATE").icon("cylinder").params("radius | diameter, height: expr; base?: [x,y,z] (centre of the bottom: numbers in mm or length expressions; default: the origin); axis?: X|Y|Z|[x,y,z] (default Z); operation?, name?, body_name?"),
-    CommandSpec::new("solid.sphere", "Sphere", prim_sphere).at("SOLID", "CREATE").icon("sphere").params("radius | diameter: expr; center?: [x,y,z] (numbers in mm or length expressions; default: the origin); operation?, name?, body_name?"),
-    CommandSpec::new("solid.torus", "Torus", prim_torus).at("SOLID", "CREATE").icon("torus").params("major, minor: expr (radii); center?: [x,y,z] (numbers in mm or length expressions; default: the origin); operation?, name?, body_name?"),
+    CommandSpec::new("solid.box", "Box", prim_box).at("SOLID", "CREATE").icon("box").params("length, width, height: expr; corner?: [x,y,z] | center?: [x,y,z] (numbers in mm or length expressions; default: the origin); operation?, targets?: [body], name?, body_name?"),
+    CommandSpec::new("solid.cylinder", "Cylinder", prim_cylinder).at("SOLID", "CREATE").icon("cylinder").params("radius | diameter, height: expr; base?: [x,y,z] (centre of the bottom: numbers in mm or length expressions; default: the origin); axis?: X|Y|Z|[x,y,z] (default Z); operation?, targets?: [body], name?, body_name?"),
+    CommandSpec::new("solid.sphere", "Sphere", prim_sphere).at("SOLID", "CREATE").icon("sphere").params("radius | diameter: expr; center?: [x,y,z] (numbers in mm or length expressions; default: the origin); operation?, targets?: [body], name?, body_name?"),
+    CommandSpec::new("solid.torus", "Torus", prim_torus).at("SOLID", "CREATE").icon("torus").params("major, minor: expr (radii); center?: [x,y,z] (numbers in mm or length expressions; default: the origin); operation?, targets?: [body], name?, body_name?"),
     CommandSpec::new("solid.fillet", "Fillet", fillet)
         .at("SOLID", "MODIFY")
         .icon("fillet")
@@ -413,9 +413,14 @@ fn add_feature_in(s: &mut Session, p: &Value, kind: FeatureKind, world: bool) ->
             solvecraft_doc::naming::face_names_at(&s.model.state(), &pts)
         }
     };
-    let participants = string_list(p, "participants");
+    // Primitives have no `targets` of their own: their `targets` are the bodies taking part (#259).
+    let primitive = matches!(kind, FeatureKind::Box { .. } | FeatureKind::Cylinder { .. } | FeatureKind::Sphere { .. } | FeatureKind::Torus { .. });
+    let (participants, key) = match string_list(p, "participants") {
+        v if v.is_empty() && primitive => (string_list(p, "targets"), "targets"),
+        v => (v, "participants"),
+    };
     if participants.len() > 10_000 || participants.iter().any(|b| b != "*" && s.model.state().body(b).is_none()) {
-        return Err(EngineError::Other("`participants` must list existing bodies".into()));
+        return Err(EngineError::Other(format!("`{key}` must list existing bodies")));
     }
     if matches!(kind, FeatureKind::ConstructionPlane { .. })
         && let Some(n) = name