Module a2a_compat 

A2A-compatible event mapping boundary for collaboration transport.

This module defines the CollaborationTransport trait that abstracts the transport layer for CollaborationEvents, and provides a LocalTransport implementation backed by an in-process broadcast channel.

A2A Concept Mapping

The collaboration event model is designed to map cleanly onto the ADK A2A protocol (see adk-server/src/a2a/types.rs) for future remote specialist execution. The mapping is:

Collaboration Concept	A2A Concept
CollaborationEvent	A2A Message or TaskStatusUpdateEvent
correlation_id	A2A task_id — links related events into one task
producer	A2A agent card sender — the agent originating the event
consumer	A2A agent card receiver — the intended recipient agent
kind	A2A TaskState or message role (see kind mapping below)
payload	A2A Artifact parts or Message parts (structured data)
topic	A2A message metadata or artifact name
timestamp	A2A event timestamp

Event Kind → A2A Task State Mapping

[CollaborationEventKind]	A2A TaskState	Notes
NeedWork	Submitted	A new task is submitted for another agent
WorkClaimed	Working	The receiving agent has accepted the task
WorkPublished	Completed + artifact	Task completed with output artifact
FeedbackRequested	InputRequired	Agent needs input before continuing
FeedbackProvided	Submitted (response)	Input provided as a new message
Blocked	InputRequired + metadata	Agent blocked, needs external decision
Completed	Completed (final)	Terminal state, no more updates

Transport Neutrality

Phase 1 uses LocalTransport (in-process broadcast channel). The event envelope is transport-neutral: the same CollaborationEvent struct works whether the transport is local or remote. A future A2aTransport would serialize events into A2A JSON-RPC messages and route them over HTTP/SSE without changing the CollaborationTransport trait contract.

Migration Path to A2A

To add remote specialist execution later:

1. Implement CollaborationTransport backed by an A2A client
2. Map CollaborationEvent → A2A Message on publish
3. Map A2A TaskStatusUpdateEvent / TaskArtifactUpdateEvent → CollaborationEvent on receive
4. Use correlation_id as the A2A task_id for routing
5. Use producer/consumer to resolve agent card URLs

The [Workspace] API remains unchanged — only the transport implementation swaps from local to remote.

Example

use adk_code::a2a_compat::{CollaborationTransport, LocalTransport};
use adk_code::{CollaborationEvent, CollaborationEventKind};

let transport = LocalTransport::new(64);
let mut receiver = transport.subscribe();

let event = CollaborationEvent::new(
    "corr-1", "api-routes", "backend", CollaborationEventKind::WorkPublished,
);
transport.publish(event).await.unwrap();

let received = receiver.recv().await;
assert!(received.is_some());

Structs

LocalTransport

In-process collaboration transport backed by a broadcast channel.

Traits

CollaborationReceiver

Async trait for receiving collaboration events from a transport.

CollaborationTransport

Async trait abstracting the collaboration event transport layer.