The original balanced_truncate function is not handling certain edge cases gracefully, leading to unintended behavior. Specifically:
- If any entry in input_dict['shortenable_ids'] was an empty list, the code could raise an IndexError when accessing parts[0].
- If total_shortenable_len was zero (e.g. no shortenable parts), a division by zero would occur during proportional calculation.
- Truncation lengths were not capped properly, which could result in slicing with negative indices.
- The function retained empty sequences post-truncation, which might be undesirable in downstream tasks.