Problem

PR #944 split EventQueue into an abstract base + concrete EventQueueLegacy, with EventQueue.__new__ redirecting EventQueue(...) to EventQueueLegacy(...) at runtime for backwards compatibility. The docstring of EventQueue shows queue = EventQueue() as typical usage.

However, mypy correctly flags this pattern as an error because EventQueue is declared abstract via ABC + @abstractmethod on enqueue_event:

error: Cannot instantiate abstract class "EventQueue" with abstract attribute "enqueue_event"  [abstract]
error: "EventQueue" has no attribute "dequeue_event"; maybe "enqueue_event"?  [attr-defined]

The methods dequeue_event, tap, close, task_done, is_closed only exist on EventQueueLegacy, not on the abstract EventQueue interface.

Result: downstream type-checked codebases (we ship a Python SDK that strict-mode-mypys every commit across 3.10–3.13) must keep importing EventQueueLegacy explicitly — the class name advertises its own deprecation, but it remains the only typeable option in a2a-sdk 1.0.1.

a2a-sdk 1.0.1 internal usage

Even a2a-sdk's own modules never instantiate EventQueue() — they all use EventQueueLegacy():

• a2a/server/events/in_memory_queue_manager.py: queue = EventQueueLegacy()
• a2a/server/events/queue_manager.py: typed as EventQueueLegacy
• a2a/server/events/event_consumer.py: typed as EventQueueLegacy
• a2a/server/request_handlers/default_request_handler.py: queue = EventQueueLegacy()

Only the docstring of EventQueue itself shows queue = EventQueue().

Requested

One of:

1. Promote EventQueue to a concrete (non-abstract) class that owns the full method surface (dequeue_event, tap, close, task_done, is_closed), making EventQueueLegacy a thin alias for the deprecation window.
2. Add a DefaultEventQueue (or similar) concrete class that downstream users can import and instantiate without the *Legacy name, with the same method surface as EventQueueLegacy.
3. Document that EventQueueLegacy is the supported instantiation surface for the foreseeable future and update the EventQueue docstring's queue = EventQueue() example accordingly so users (and type-checkers) aren't misled.

We don't have a preference on which path — any of the three unblocks the rename downstream.

Downstream tracking

adcontextprotocol/adcp-client-python#699 (left a TODO in our harness pointing at this issue).