Fix self-referential shapes (CategoryShape)

Set field-only _spec before building the full spec with nested shapes.
Self-references resolve because cls._spec already exists when the
generator encounters shape._spec where shape is cls.

Also: pass cls into get_type_hints localns so forward ref strings
like list["CategoryShape"] resolve to the class being defined.

49 shapes tests, 0 skipped.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

django/src/djarea/tests/test_shapes.py

@@ -105,13 +105,10 @@ class BookWithEditorShape(Shape[Book]):
     editor: FlatAuthorShape | None = None
 
 
-# CategoryShape is commented out — self-referential forward refs crash
-# get_type_hints() at __init_subclass__ time. Known gap.
-#
-# class CategoryShape(Shape[Category]):
-#     id: int | None = None
-#     name: str
-#     children: list["CategoryShape"] = []
+class CategoryShape(Shape[Category]):
+    id: int | None = None
+    name: str
+    children: list["CategoryShape"] = []
 
 
 # =============================================================================
@@ -169,11 +166,9 @@ class TestShapeClassCreation(TestCase):
             )
 
     def test_self_referential_shape(self):
-        """CategoryShape.children references itself.
-        Currently crashes at class definition time — known gap."""
-        self.skipTest(
-            "Self-referential forward ref crashes get_type_hints() at __init_subclass__ time"
-        )
+        """CategoryShape.children references itself."""
+        self.assertIn("children", CategoryShape._nested)
+        self.assertIs(CategoryShape._nested["children"], CategoryShape)
 
     def test_multiple_shapes_same_model_independent(self):
         self.assertLess(len(FlatBookShape._field_names), len(BookDetailShape._field_names))