The salvaged test double predated two main changes:
- start() now connects via _connect_adapter_with_timeout, which forwards
is_reconnect to adapter.connect(); the StartupRaceAdapter double didn't
accept the kwarg.
- stop() now awaits _finalize_shutdown_agents (async on main); the fixture
stubbed it as a plain MagicMock.
Accept is_reconnect in the double and use AsyncMock for the finalize stub.