- Extracted delta event batching and throttling logic into AssistantMessageEventStream base class to eliminate duplication across test mocks.
- Changed access modifiers from private to protected in EventStream class to allow subclass customization of queue, waiting, and completion handling.
- Simplified MockAssistantStream implementations across five test files by removing custom event handling logic and delegating to AssistantMessageEventStream.
- Added protected methods deliver() and endWaiting() to EventStream to support subclass event delivery patterns.
- Implemented delta event type guard and merging utilities to consolidate event batching logic in one place.