Map Helix in the Python host model; record DXF handedness blocker

The host rebuilds the derived spline from the generating parameters on
scripted create/edit. staged_python_helix_lifecycle_over_real_ipc passes
every gate except DXF handedness, which acadrust's reader never applies;
the gap is pinned by a canary via per-format expectations in the shared
mesh lifecycle driver.

Co-Authored-By: Claude Sonnet 5 <[email protected]>

plugins/opencad-python/README.md

@@ -94,7 +94,7 @@ The host-owned catalog classifies all 48 entity variants and tracks every
 traced field, including fields marked `unmapped`. Query it with
 `doc.coverage()` or `doc.coverage("Line")`; each row includes source field,
 type, access, and current validation status. Geometry edits remain limited to
-the 30 mapped kinds.
+the 31 mapped kinds.
 For any entity, `entity.snapshot` returns a detached dictionary of its raw
 CAD fields, including `snapshot["common"]` and kind-specific nested values.
 It can inspect an unmapped kind; editing the dictionary does

plugins/opencad-python/entity_manifest.json

@@ -29,7 +29,8 @@
     "Table",
     "PolygonMesh",
     "PolyfaceMesh",
-    "Mesh"
+    "Mesh",
+    "Helix"
   ],
   "manual_kinds": ["Dimension"],
   "base_fields": ["handle", "layer", "owner_handle"],
@@ -331,6 +332,14 @@
         "faces": { "required": true },
         "version": { "read_only": true }
       }
+    },
+    "Helix": {
+      "fields": {
+        "start_point": { "required": true },
+        "spline": { "read_only": true, "_comment": "Derived by the host from the generating parameters." },
+        "major_version": { "read_only": true },
+        "maintenance_version": { "read_only": true }
+      }
     }
   }
 }

plugins/opencad-python/src/ocs_module.rs

@@ -4756,7 +4756,7 @@ mod tests {
                 );
             }
         }
-        assert_eq!(emitted.len(), 30);
+        assert_eq!(emitted.len(), 31);
     }
 
     #[cfg(feature = "experimental-host-model")]