Add Form() annotations and fix OpenAPI generation for multipart params

- Add Form() annotations to purpose and expires_after parameters in file upload endpoints
- Add support for optional multipart form parameters in OpenAPI generator
- Generated spec now properly mirrors OpenAI format with schema refs

llama_stack/apis/files/files.py

@@ -7,7 +7,7 @@
 from enum import StrEnum
 from typing import Annotated, ClassVar, Literal, Protocol, runtime_checkable
 
-from fastapi import File, Response, UploadFile
+from fastapi import File, Form, Response, UploadFile
 from pydantic import BaseModel, Field
 
 from llama_stack.apis.common.responses import Order
@@ -110,9 +110,8 @@ class Files(Protocol):
     async def openai_upload_file(
         self,
         file: Annotated[UploadFile, File()],
-        purpose: OpenAIFilePurpose,
-        expires_after: ExpiresAfter | None = None,
-        # TODO: expires_after is producing strange openapi spec, params are showing up as a required w/ oneOf being null
+        purpose: Annotated[OpenAIFilePurpose, Form()],
+        expires_after: Annotated[ExpiresAfter | None, Form()] = None,
     ) -> OpenAIFileObject:
         """
         Upload a file that can be used across various endpoints.

llama_stack/providers/inline/files/localfs/files.py

@@ -9,7 +9,7 @@ import uuid
 from pathlib import Path
 from typing import Annotated
 
-from fastapi import File, Response, UploadFile
+from fastapi import File, Form, Response, UploadFile
 
 from llama_stack.apis.common.errors import ResourceNotFoundError
 from llama_stack.apis.common.responses import Order
@@ -86,8 +86,8 @@ class LocalfsFilesImpl(Files):
     async def openai_upload_file(
         self,
         file: Annotated[UploadFile, File()],
-        purpose: OpenAIFilePurpose,
-        expires_after: ExpiresAfter | None = None,
+        purpose: Annotated[OpenAIFilePurpose, Form()],
+        expires_after: Annotated[ExpiresAfter | None, Form()] = None,
     ) -> OpenAIFileObject:
         """Upload a file that can be used across various endpoints."""
         if not self.sql_store:

llama_stack/providers/remote/files/s3/files.py

@@ -10,7 +10,7 @@ from typing import Annotated, Any
 
 import boto3
 from botocore.exceptions import BotoCoreError, ClientError, NoCredentialsError
-from fastapi import File, Response, UploadFile
+from fastapi import File, Form, Response, UploadFile
 
 from llama_stack.apis.common.errors import ResourceNotFoundError
 from llama_stack.apis.common.responses import Order
@@ -194,8 +194,8 @@ class S3FilesImpl(Files):
     async def openai_upload_file(
         self,
         file: Annotated[UploadFile, File()],
-        purpose: OpenAIFilePurpose,
-        expires_after: ExpiresAfter | None = None,
+        purpose: Annotated[OpenAIFilePurpose, Form()],
+        expires_after: Annotated[ExpiresAfter | None, Form()] = None,
     ) -> OpenAIFileObject:
         file_id = f"file-{uuid.uuid4().hex}"
 

llama_stack/strong_typing/inspection.py

@@ -567,6 +567,20 @@ 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
+        from pydantic.fields import FieldInfo
+
+        def get_field_type(name: str, field) -> 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)
+                return Annotated[field.annotation, field_info]
+            return field.annotation
+
+        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

@@ -93,6 +93,11 @@ def get_class_property_docstrings(
     """
 
     result = {}
+    # 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():