M3.20: visual bounds cover arrowheads so overhanging heads are not culled; one arrowhead-weight helper

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

crates/engine/src/tests_strokegeom.rs

@@ -49,6 +49,13 @@ fn profiles_come_from_the_preset_catalogue() {
         assert!(spec.params.contains(&format!("\"{}\"", p.id)), "{}", p.id);
     }
     assert!(spec.params.contains("arrowAlign"));
+    // …and every arrowhead name `startArrow`/`endArrow` accept.
+    for a in vectorcraft_doc::Arrowhead::ALL {
+        let name = serde_json::to_value(a).unwrap();
+        assert!(spec.params.contains(name.as_str().unwrap()), "{name}");
+        s.execute("stroke.set", &json!({"endArrow": name})).unwrap();
+        assert_eq!(stroke(&s, id).end_arrow, Some(a));
+    }
 }
 
 #[test]