diff --git a/django/pyproject.toml b/django/pyproject.toml
index dc6a579..0a20580 100644
--- a/django/pyproject.toml
+++ b/django/pyproject.toml
@@ -7,6 +7,7 @@ requires-python = ">=3.10"
 dependencies = [
     "django>=5.0",
     "django-ninja>=1.0",
+    "django-readers>=2.0",
     "pydantic>=2.0",
     "PyJWT>=2.0",
 ]
diff --git a/django/src/djarea/__init__.py b/django/src/djarea/__init__.py
index dbbe155..ebf0901 100644
--- a/django/src/djarea/__init__.py
+++ b/django/src/djarea/__init__.py
@@ -89,10 +89,8 @@ from . import setup
 from .channels import ReactChannel
 from .channels import register as register_channel
 from .client import ComposedContext, ServerFunction, client, compose
-try:
-    from .shapes import Shape
-except ImportError:
-    pass  # django-readers not installed
+    # Shape is lazy-loaded via __getattr__ because django_readers
+    # imports contenttypes, which can't happen during apps.populate()
 from .setup import (
     djarea_clients,
     djarea_module,
@@ -104,11 +102,15 @@ from .setup import (
 
 
 def __getattr__(name):
-    """Lazy loading for urls to avoid circular imports."""
+    """Lazy loading for modules that can't be imported at app load time."""
     if name == "urls":
         from .urls import urlpatterns as djarea_patterns
 
         return djarea_patterns
+    if name == "Shape":
+        from .shapes import Shape
+
+        return Shape
     raise AttributeError(f"module {__name__!r} has no attribute {name!r}")
 
 
diff --git a/django/src/djarea/tests/test_shapes.py b/django/src/djarea/tests/test_shapes.py
new file mode 100644
index 0000000..7e5a9a1
--- /dev/null
+++ b/django/src/djarea/tests/test_shapes.py
@@ -0,0 +1,285 @@
+"""
+Tests for djarea.shapes — Pydantic API surface for Django models.
+
+Uses real Django models (Author, Book, Tag) and real database queries.
+"""
+
+from django.test import TestCase
+
+from djarea.shapes import Shape, Diff, NestedDiff
+
+from tests.models import Author, Book, Tag
+
+
+# =============================================================================
+# Shape definitions
+# =============================================================================
+
+
+class BookShape(Shape[Book]):
+    id: int | None = None
+    title: str
+    pages: int
+
+
+class AuthorShape(Shape[Author]):
+    id: int | None = None
+    name: str
+    bio: str
+    books: list[BookShape] = []
+
+
+class FlatAuthorShape(Shape[Author]):
+    """Author without nested books."""
+    id: int | None = None
+    name: str
+
+
+# =============================================================================
+# Shape class construction
+# =============================================================================
+
+
+class ShapeMetaTests(TestCase):
+    """Shape __init_subclass__ correctly extracts metadata."""
+
+    def test_model_resolved(self):
+        self.assertEqual(AuthorShape._model, Author)
+        self.assertEqual(BookShape._model, Book)
+
+    def test_field_names_extracted(self):
+        self.assertEqual(BookShape._field_names, ["id", "title", "pages"])
+
+    def test_nested_detected(self):
+        self.assertIn("books", AuthorShape._nested)
+        self.assertEqual(AuthorShape._nested["books"], BookShape)
+
+    def test_flat_shape_has_no_nested(self):
+        self.assertEqual(FlatAuthorShape._nested, {})
+
+    def test_spec_built(self):
+        self.assertIsInstance(BookShape._spec, list)
+        self.assertIn("title", BookShape._spec)
+        self.assertIn("pages", BookShape._spec)
+
+    def test_pair_built(self):
+        self.assertIsNotNone(BookShape._pair)
+        self.assertEqual(len(BookShape._pair), 2)  # (prepare, project)
+
+
+# =============================================================================
+# Querying
+# =============================================================================
+
+
+class ShapeQueryTests(TestCase):
+    """Shape.query() runs real ORM queries and returns typed results."""
+
+    def setUp(self):
+        self.author = Author.objects.create(name="Alice", bio="Writer")
+        self.book1 = Book.objects.create(title="Book One", pages=100, author=self.author)
+        self.book2 = Book.objects.create(title="Book Two", pages=200, author=self.author)
+
+    def test_query_returns_list_of_shapes(self):
+        results = BookShape.query()
+        self.assertEqual(len(results), 2)
+        self.assertIsInstance(results[0], BookShape)
+
+    def test_query_field_values(self):
+        results = BookShape.query()
+        titles = {b.title for b in results}
+        self.assertEqual(titles, {"Book One", "Book Two"})
+
+    def test_query_with_filter(self):
+        results = BookShape.query(Book.objects.filter(pages__gte=150))
+        self.assertEqual(len(results), 1)
+        self.assertEqual(results[0].title, "Book Two")
+        self.assertEqual(results[0].pages, 200)
+
+    def test_query_returns_ids(self):
+        results = BookShape.query()
+        for book in results:
+            self.assertIsNotNone(book.id)
+            self.assertIsInstance(book.id, int)
+
+    def test_flat_author_query(self):
+        results = FlatAuthorShape.query()
+        self.assertEqual(len(results), 1)
+        self.assertEqual(results[0].name, "Alice")
+
+    def test_nested_query(self):
+        results = AuthorShape.query()
+        self.assertEqual(len(results), 1)
+
+        author = results[0]
+        self.assertEqual(author.name, "Alice")
+        self.assertEqual(len(author.books), 2)
+        self.assertIsInstance(author.books[0], BookShape)
+
+        titles = {b.title for b in author.books}
+        self.assertEqual(titles, {"Book One", "Book Two"})
+
+    def test_empty_query(self):
+        results = BookShape.query(Book.objects.none())
+        self.assertEqual(results, [])
+
+    def test_query_returns_pydantic_models(self):
+        results = BookShape.query()
+        book = results[0]
+        # Can serialize to dict
+        d = book.model_dump()
+        self.assertIn("title", d)
+        self.assertIn("pages", d)
+        self.assertIn("id", d)
+
+
+# =============================================================================
+# Diff
+# =============================================================================
+
+
+class DiffNewTests(TestCase):
+    """Diff for new objects (no id)."""
+
+    def test_new_object_is_new(self):
+        shape = BookShape(title="New Book", pages=50)
+        diff = shape.diff()
+
+        self.assertTrue(diff.is_new)
+        self.assertEqual(diff.changed["title"], "New Book")
+        self.assertEqual(diff.changed["pages"], 50)
+        self.assertNotIn("id", diff.changed)
+
+
+class DiffExistingTests(TestCase):
+    """Diff for existing objects detects changes."""
+
+    def setUp(self):
+        self.author = Author.objects.create(name="Alice", bio="Writer")
+        self.book = Book.objects.create(title="Original", pages=100, author=self.author)
+
+    def test_no_changes(self):
+        shape = BookShape(id=self.book.id, title="Original", pages=100)
+        diff = shape.diff()
+
+        self.assertFalse(diff.is_new)
+        self.assertEqual(diff.changed, {})
+
+    def test_title_changed(self):
+        shape = BookShape(id=self.book.id, title="Updated", pages=100)
+        diff = shape.diff()
+
+        self.assertFalse(diff.is_new)
+        self.assertEqual(diff.changed, {"title": "Updated"})
+
+    def test_multiple_changes(self):
+        shape = BookShape(id=self.book.id, title="Updated", pages=999)
+        diff = shape.diff()
+
+        self.assertEqual(diff.changed, {"title": "Updated", "pages": 999})
+
+    def test_nonexistent_id_raises(self):
+        shape = BookShape(id=99999, title="Ghost", pages=0)
+        with self.assertRaises(Book.DoesNotExist):
+            shape.diff()
+
+
+class DiffNestedTests(TestCase):
+    """Diff for shapes with nested relations."""
+
+    def setUp(self):
+        self.author = Author.objects.create(name="Alice", bio="Writer")
+        self.book1 = Book.objects.create(title="Book One", pages=100, author=self.author)
+        self.book2 = Book.objects.create(title="Book Two", pages=200, author=self.author)
+
+    def test_nested_no_changes(self):
+        shape = AuthorShape(
+            id=self.author.id,
+            name="Alice",
+            bio="Writer",
+            books=[
+                BookShape(id=self.book1.id, title="Book One", pages=100),
+                BookShape(id=self.book2.id, title="Book Two", pages=200),
+            ],
+        )
+        diff = shape.diff()
+
+        self.assertFalse(diff.is_new)
+        self.assertEqual(diff.changed, {})
+        self.assertEqual(diff.books.created, [])
+        self.assertEqual(diff.books.updated, [])
+        self.assertEqual(diff.books.deleted, [])
+
+    def test_nested_created(self):
+        shape = AuthorShape(
+            id=self.author.id,
+            name="Alice",
+            bio="Writer",
+            books=[
+                BookShape(id=self.book1.id, title="Book One", pages=100),
+                BookShape(id=self.book2.id, title="Book Two", pages=200),
+                BookShape(title="New Book", pages=50),  # no id = new
+            ],
+        )
+        diff = shape.diff()
+
+        self.assertEqual(len(diff.books.created), 1)
+        self.assertEqual(diff.books.created[0].title, "New Book")
+
+    def test_nested_updated(self):
+        shape = AuthorShape(
+            id=self.author.id,
+            name="Alice",
+            bio="Writer",
+            books=[
+                BookShape(id=self.book1.id, title="Updated Title", pages=100),
+                BookShape(id=self.book2.id, title="Book Two", pages=200),
+            ],
+        )
+        diff = shape.diff()
+
+        self.assertEqual(len(diff.books.updated), 1)
+        self.assertEqual(diff.books.updated[0].title, "Updated Title")
+
+    def test_nested_deleted(self):
+        shape = AuthorShape(
+            id=self.author.id,
+            name="Alice",
+            bio="Writer",
+            books=[
+                BookShape(id=self.book1.id, title="Book One", pages=100),
+                # book2 missing = deleted
+            ],
+        )
+        diff = shape.diff()
+
+        self.assertEqual(diff.books.deleted, [self.book2.id])
+
+    def test_nested_combined(self):
+        """Create, update, and delete in one diff."""
+        shape = AuthorShape(
+            id=self.author.id,
+            name="Alice",
+            bio="Writer",
+            books=[
+                BookShape(id=self.book1.id, title="Renamed", pages=100),  # updated
+                BookShape(title="Brand New", pages=10),  # created
+                # book2 missing = deleted
+            ],
+        )
+        diff = shape.diff()
+
+        self.assertEqual(len(diff.books.created), 1)
+        self.assertEqual(len(diff.books.updated), 1)
+        self.assertEqual(diff.books.deleted, [self.book2.id])
+
+    def test_accessing_nonexistent_nested_returns_empty(self):
+        shape = BookShape(title="Simple", pages=10)
+        diff = shape.diff()
+
+        # BookShape has no nested relations
+        empty = diff.nonexistent_relation
+        self.assertIsInstance(empty, NestedDiff)
+        self.assertEqual(empty.created, [])
+        self.assertEqual(empty.updated, [])
+        self.assertEqual(empty.deleted, [])
diff --git a/django/tests/models.py b/django/tests/models.py
index 6aaa8d2..4ac6e1f 100644
--- a/django/tests/models.py
+++ b/django/tests/models.py
@@ -38,3 +38,37 @@ class EmailUser(AbstractBaseUser, PermissionsMixin):
 
     class Meta:
         app_label = "tests"
+
+
+# ─── Shape test models ──────────────────────────────────────────────────────
+
+
+class Author(models.Model):
+    name = models.CharField(max_length=100)
+    bio = models.TextField(blank=True, default="")
+
+    class Meta:
+        app_label = "tests"
+
+    def __str__(self):
+        return self.name
+
+
+class Book(models.Model):
+    title = models.CharField(max_length=200)
+    pages = models.IntegerField(default=0)
+    author = models.ForeignKey(Author, on_delete=models.CASCADE, related_name="books")
+
+    class Meta:
+        app_label = "tests"
+
+    def __str__(self):
+        return self.title
+
+
+class Tag(models.Model):
+    name = models.CharField(max_length=50)
+    books = models.ManyToManyField(Book, related_name="tags", blank=True)
+
+    class Meta:
+        app_label = "tests"