@mock_only
Feature: A2aEventQueue thread-safety (issue #7604)
  As a CleverAgents developer
  I want A2aEventQueue to be safe for concurrent use from multiple threads
  So that publish/subscribe/unsubscribe operations never raise
  RuntimeError: dictionary changed size during iteration

  # -----------------------------------------------------------------------
  # Regression: concurrent publish + subscribe must not raise RuntimeError
  # -----------------------------------------------------------------------

  Scenario: Concurrent publish and subscribe_local do not raise RuntimeError
    Given a2aconcur a fresh A2aEventQueue
    When a2aconcur I run concurrent publish and subscribe_local from multiple threads
    Then a2aconcur no RuntimeError should have been raised
    And a2aconcur all published events should be in the queue

  # -----------------------------------------------------------------------
  # Regression: concurrent publish + unsubscribe must not raise RuntimeError
  # -----------------------------------------------------------------------

  Scenario: Concurrent publish and unsubscribe do not raise RuntimeError
    Given a2aconcur a fresh A2aEventQueue with subscribers
    When a2aconcur I run concurrent publish and unsubscribe from multiple threads
    Then a2aconcur no RuntimeError should have been raised

  # -----------------------------------------------------------------------
  # Regression: concurrent subscribe + unsubscribe must not raise RuntimeError
  # -----------------------------------------------------------------------

  Scenario: Concurrent subscribe_local and unsubscribe do not raise RuntimeError
    Given a2aconcur a fresh A2aEventQueue
    When a2aconcur I run concurrent subscribe_local and unsubscribe from multiple threads
    Then a2aconcur no RuntimeError should have been raised

  # -----------------------------------------------------------------------
  # Lock is present on new instances
  # -----------------------------------------------------------------------

  Scenario: A2aEventQueue has a threading.Lock after construction
    Given a2aconcur a fresh A2aEventQueue
    Then a2aconcur the queue should have a threading Lock attribute

  # -----------------------------------------------------------------------
  # publish snapshots subscriptions so late-arriving unsubscribe is safe
  # -----------------------------------------------------------------------

  Scenario: Unsubscribing inside a callback does not affect the current publish iteration
    Given a2aconcur a fresh A2aEventQueue
    And a2aconcur a subscriber that unsubscribes itself during the callback
    When a2aconcur I publish a valid A2aEvent
    Then a2aconcur no RuntimeError should have been raised
    And a2aconcur the event should be in the queue

  # -----------------------------------------------------------------------
  # get_events is thread-safe
  # -----------------------------------------------------------------------

  Scenario: Concurrent publish and get_events do not raise RuntimeError
    Given a2aconcur a fresh A2aEventQueue
    When a2aconcur I run concurrent publish and get_events from multiple threads
    Then a2aconcur no RuntimeError should have been raised