Summary

This PR resolves a memory leak in the auto-suggestion subsystem of the terminal interactive shell, fixes an incorrect default value in the prefixer, and improves robustness against cancellations and API errors.

Changes

1. Memory Leak Fix: The disconnect method of NavigableAutoSuggestFromHistory was updated to remove _dismiss from the buffer's on_cursor_position_changed event. Previously, only the on_text_insert handler was removed, resulting in a leak where the auto-suggester remained referenced by the event.
2. Default Prefixer Fix: Changed _llm_prefixer default implementation from returning "wrong" to "".
3. Execution Robustness: Wrapped await self._llm_task execution in a try-except block to catch asyncio.CancelledError and Exception. This ensures that natural task cancellations (during cursor movement) or LLM provider errors do not bubble up to prompt_toolkit and crash the prompt.

Testing Checklist

• Verify on_cursor_position_changed handler is removed upon disconnect.
• Verify trigger routine gracefully handles task cancellation without throwing CancelledError.
• Verify trigger routine gracefully catches and suppresses provider exceptions.