Replace hasattr() duck-typing with isinstance() checks for DiscordAdapter
in gateway/run.py, add TypedDict for IMAGEGEN_BACKENDS in tools_config.py,
properly type fal_client getattr'd callables in image_generation_tool.py,
fix dict[str, object] → Callable annotation in approval.py, use
isinstance(BaseModel) in web_tools.py, capture _message_handler to local
in base.py, rename shadowed list_distributions parameter in batch_runner.py,
and remove dead queue_message branch.
f8d2365795