Best practice for exposing Remote A2A Agent state and UI metadata to the calling ADK agent

[rivkav]

Title: Best practice for exposing Remote A2A Agent state and UI metadata to the calling ADK agent

Hi,

I'm building a multi-agent system with Google ADK where one ADK agent communicates with an external agent through RemoteA2aAgent.

The external agent is not just returning a final result. It has a long-running workflow and exposes information such as:

• Current workflow state
• Progress
• Current step
• Next expected action
• Dynamic UI controls (buttons, forms, etc.)
• Other metadata that the calling agent can use to decide how to continue the conversation.

After reading the A2A specification, I'm still unsure what the recommended approach is for this kind of information.

My questions are:

1. Is there an official or recommended pattern for exposing agent state through A2A?
2. Should this information be placed in metadata, artifacts, or somewhere else?
3. If the information is not part of the user's final output but rather represents the execution state of the remote agent, what is the intended location?
4. Is there a recommended contract for exposing dynamic UI information (buttons, forms, next actions) so that different agents can interoperate consistently?
5. If multiple remote agents are integrated, is there a best practice for keeping a consistent response contract across all of them?

My goal is to define a standardized contract that every external agent can implement, allowing the calling ADK agent to understand the remote agent's state without requiring custom logic for each integration.

I'd appreciate any guidance or examples of recommended patterns.