- Added `UserTurnCompletionLLMServiceMixin` for LLM services to detect and filter incomplete user turns. When enabled via `filter_incomplete_user_turns` in `LLMUserAggregatorParams`, the LLM outputs a turn completion marker at the start of each response: ✓ (complete), ○ (incomplete short), or ◐ (incomplete long). Incomplete turns are suppressed, and configurable timeouts automatically re-prompt the user.