chore: import upstream snapshot with attribution

tools/protocols.py

@@ -0,0 +1,35 @@
+"""Structural typing contracts for rendering backends.
+
+Any class that exposes the right method signatures satisfies these
+protocols -- no inheritance required. Existing generators (Google,
+Yunwu/Doubao, Yunwu/Veo) are already compliant by duck typing.
+"""
+
+from typing import List, Protocol, runtime_checkable
+
+from interfaces.image_output import ImageOutput
+from interfaces.video_output import VideoOutput
+
+
+@runtime_checkable
+class ImageGenerator(Protocol):
+    """Generates a single image from a text prompt and optional reference images."""
+
+    async def generate_single_image(
+        self,
+        prompt: str,
+        reference_image_paths: List[str],
+        **kwargs,
+    ) -> ImageOutput: ...
+
+
+@runtime_checkable
+class VideoGenerator(Protocol):
+    """Generates a single video from a text prompt and optional reference images."""
+
+    async def generate_single_video(
+        self,
+        prompt: str,
+        reference_image_paths: List[str],
+        **kwargs,
+    ) -> VideoOutput: ...