Mechanism to defer `UIResource` rendering for intermediate tool calls

Summary

The current specification does not clearly define the expected Host behavior when a model executes multiple tool calls, each returning a UIResource.

Questions

1. Rendering multiple UIResources: If the model runs N tool calls, each with an associated UIResource, should the Host render N iframes? Or is it up to the Host to decide how and when to display these UIs?

2. Priority field behavior: The MCP spec includes a priority annotation (0.0 to 1.0), but it's unclear:

   • What is the expected behavior when priority is not set?
   • What should Hosts do when all UIResources have the same priority (e.g., all 1.0)?
   • How does priority apply to UI rendering decisions specifically?

Understanding the intended behavior would help ensure consistent UX across different Host implementations.