Add Server-Sent Events (SSE) streaming infrastructure to the A2A
event system, enabling real-time delivery of task status updates
and artifact notifications.
Key changes:
- Defined SSE event type constants: TASK_STATUS_UPDATE
(TaskStatusUpdateEvent) and TASK_ARTIFACT_UPDATE
(TaskArtifactUpdateEvent) per the A2A protocol specification.
- Added SseEventFormatter class that converts A2aEvent instances
to text/event-stream format with event, id, and data fields.
Includes keepalive formatting for long-lived connections.
- Added EventBusBridge class that subscribes to the internal
EventBus (ReactiveEventBus) and translates DomainEvent instances
into A2aEvent instances published to the A2aEventQueue. Maps
plan lifecycle events (PLAN_CREATED, PLAN_PHASE_CHANGED, etc.)
to TaskStatusUpdateEvent and checkpoint events to
TaskArtifactUpdateEvent.
- Bridge handles closed queue gracefully via contextlib.suppress.
- Added 8 Behave scenarios covering SSE formatting, event type
constants, EventBusBridge translation for both status and
artifact events, closed queue handling, and JSON payload
validation.
ISSUES CLOSED: #875
freemo