fix(codegen): expand union member trees before collecting types

extract_model() on union members produced ModelSpecs with model=None
on MODEL-kind fields. _collect_from_fields then hit the RuntimeError
guard when it encountered those unexpanded references. Call
expand_model_tree() on each member before walking its fields.

No current union members have sub-model fields, so this was latent.

Author: sethfitz

packages/overture-schema-codegen/src/overture/schema/codegen/type_collection.py

@@ -8,7 +8,7 @@
 from typing import Annotated, get_args, get_origin
 
 from .enum_extraction import extract_enum
-from .model_extraction import extract_model
+from .model_extraction import expand_model_tree, extract_model
 from .newtype_extraction import extract_newtype
 from .pydantic_extraction import extract_pydantic_type
 from .specs import (
@@ -93,6 +93,7 @@ def _visit(node: TypeInfo) -> None:
                 # by the feature_objs guard in _collect_from_model.
                 for member_cls in node.union_members:
                     member_spec = extract_model(member_cls)
+                    expand_model_tree(member_spec)
                     _collect_from_model(member_spec)
 
             if node.kind == TypeKind.ENUM and node.source_type is not None:

packages/overture-schema-codegen/tests/codegen_test_support.py

@@ -237,6 +237,26 @@ class WaterSegment(SegmentBase):
 ]
 
 
+class ContactInfo(BaseModel):
+    """Contact information for a venue."""
+
+    email: str = Field(description="Email address")
+    phone: str | None = Field(None, description="Phone number")
+
+
+class VenueWithContact(SegmentBase):
+    """A segment variant with a nested sub-model field."""
+
+    subtype: Literal["venue"]
+    contact: ContactInfo
+
+
+TestSegmentWithSubModel = Annotated[
+    RoadSegment | VenueWithContact,
+    Field(description="Test segment union with sub-model member"),
+]
+
+
 def make_union_spec(
     name: str = "TestUnion",
     *,

packages/overture-schema-codegen/tests/test_type_collection.py

@@ -5,6 +5,7 @@
     FeatureWithSources,
     FeatureWithUrl,
     Instrument,
+    TestSegmentWithSubModel,
     has_name,
     lookup_by_name,
 )
@@ -85,6 +86,21 @@ def test_same_name_different_types_both_collected(self) -> None:
         assert len(address_entries) == 2
 
 
+class TestCollectUnionMemberSubModels:
+    """Tests for union members with nested sub-model fields."""
+
+    def test_union_member_with_sub_model_collects_sub_model(self) -> None:
+        """Sub-models inside union members are collected without RuntimeError."""
+
+        class FeatureWithUnionSubModel(BaseModel):
+            segment: TestSegmentWithSubModel
+
+        result = _expanded_supplementary(FeatureWithUnionSubModel)
+
+        assert has_name(result, "ContactInfo")
+        assert isinstance(lookup_by_name(result, "ContactInfo"), ModelSpec)
+
+
 class TestCollectPydanticTypes:
     """Tests for Pydantic built-in type collection."""