make a list of a2ui messages a top level construct

[wrenj]

this keeps coming up:
mcp tool responses are a single object, but we need a list of a2ui messages
a2a data part is a single object, but we need a list of a2ui messages
etc

[jacobsimionato]

I agree that a definition of an A2UI layout needs multiple messages and so we should define how to package them for each transport.

I want to avoid having redundant lists at multiple levels of the data structure, because that creates ambiguity around the right way to map A2UI messages to transports. E.g. updateComponents already has a list of components, then in A2A there is also a list of Parts within each Message. If we add another array layer in there, then there's a lot of ambiguity.

What about this:

A2A transport (and other transports with a concept of 'part')

1. A2UI Message
2. A2A Data Part (array, used to represent
3. A2A Message (singular, transported atomically)

MCP transport (and other transports that represent UIs a single blob)

1. A2UI Message
2. A2UI Resource (new concept, contains an array of messages)
3. MCP response

[jacobsimionato]

@gspencergoog

[gspencergoog]

The solution I have used here is to put JSONL in the data parts and output, not JSON. Then it's an open-ended array by definition, but no syntax or extra layers need to be added.

[wrenj]

whats this look like?

here is how we encode the a2ui output now:
https://github.com/google/A2UI/blob/main/a2a_agents/python/a2ui_agent/src/a2ui/extension/a2ui_extension.py#L35

it just takes in a dict which represents a single createSurface/updateComponents/etc

are you saying just pass in an array of dicts instead?

[gspencergoog]

are you saying just pass in an array of dicts instead?

Yes, basically. You might have to change how you prompt ("generate JSONL" instead of "generate JSON"), or you can just have it generate a JSON array of messages. The code already handles that anyhow.

[jacobsimionato]

The solution I have used here is to put JSONL in the data parts and output, not JSON. Then it's an open-ended array by definition, but no syntax or extra layers need to be added.

I'm fine with this approach! We can change the guidance in the A2UI + A2A transport documentation to suggest that each A2A message should have maximum one A2UI message parts, which include an array of messages that are applied atomically in order. I mostly just think we should make it unambiguous how to map A2UI on to A2A.

The section to update is here:
https://github.com/google/A2UI/blob/main/specification/v0_9/docs/a2ui_extension_specification.md#data-encoding

[wrenj]

okay sounds good, ill move everything to arrays, ill probably make a container for it too

to be clear, when you say JSONL, it just means wrapping the schema in {"type": "array", "items": a2ui_schema}

https://github.com/google/A2UI/blob/main/samples/agent/adk/mcp/server.py#L42

[wrenj]

I see, so the issue with JSONL is examples like here
https://github.com/google/A2UI/blob/main/samples/agent/adk/rizzcharts/examples/standard_catalog/chart.json

would have to be on a single line which would be very human-unreadable. likewise we have to make sure the LLM isn't emitting any newlines in its output.

do you still think jsonl is the best way to go?

[wrenj]

Also the transports don't accept a list of dicts, eg datapart takes a dict
https://github.com/google/A2UI/blob/main/a2a_agents/python/a2ui_agent/src/a2ui/extension/a2ui_extension.py#L48

let me make a top level construct to encapsulate an array of a2ui messages

[wrenj]

okay sent #576 please take a look, thanks