feat(files): fix expires_after API shape (#3604)

This was just quite incorrect. See source here:
https://platform.openai.com/docs/api-reference/files/create

llama_stack/strong_typing/inspection.py

@@ -567,6 +567,22 @@ def get_class_properties(typ: type) -> Iterable[Tuple[str, type | str]]:
 
     if is_dataclass_type(typ):
         return ((field.name, field.type) for field in dataclasses.fields(typ))
+    elif hasattr(typ, "model_fields"):
+        # Pydantic BaseModel - use model_fields to exclude ClassVar and other non-field attributes
+        # Reconstruct Annotated type if discriminator exists to preserve metadata
+        from typing import Annotated, Any, cast
+        from pydantic.fields import FieldInfo
+
+        def get_field_type(name: str, field: Any) -> type | str:
+            # If field has discriminator, wrap in Annotated to preserve it for schema generation
+            if field.discriminator:
+                field_info = FieldInfo(annotation=None, discriminator=field.discriminator)
+                # Annotated returns _AnnotatedAlias which isn't a type but is valid here
+                return Annotated[field.annotation, field_info]  # type: ignore[return-value]
+            # field.annotation can be Union types, Annotated, etc. which aren't type but are valid
+            return field.annotation  # type: ignore[return-value,no-any-return]
+
+        return ((name, get_field_type(name, field)) for name, field in typ.model_fields.items())
     else:
         resolved_hints = get_resolved_hints(typ)
         return resolved_hints.items()

llama_stack/strong_typing/schema.py

@@ -92,7 +92,12 @@ def get_class_property_docstrings(
     :returns: A dictionary mapping property names to descriptions.
     """
 
-    result = {}
+    result: Dict[str, str] = {}
+    # Only try to get MRO if data_type is actually a class
+    # Special types like Literal, Union, etc. don't have MRO
+    if not inspect.isclass(data_type):
+        return result
+
     for base in inspect.getmro(data_type):
         docstr = docstring.parse_type(base)
         for param in docstr.params.values():