def working_position_label(ss_idx: int, num_supersets: int) -> str:
    """Return early/middle/late position label for a working superset index."""
    if num_supersets <= 1 or ss_idx == 0:
        return 'early'
    if ss_idx >= num_supersets - 1:
        return 'late'
    return 'middle'


def merge_pattern_preferences(position_patterns, rule_patterns):
    """Combine positional and structure-rule pattern preferences."""
    if rule_patterns and position_patterns:
        overlap = [p for p in position_patterns if p in rule_patterns]
        return overlap or rule_patterns[:3]
    if rule_patterns:
        return rule_patterns[:3]
    return position_patterns


def rotated_muscle_subset(target_muscles: list[str], ss_idx: int) -> list[str]:
    """Rotate target muscle emphasis between supersets."""
    if len(target_muscles) <= 1:
        return target_muscles
    start = ss_idx % len(target_muscles)
    return target_muscles[start:] + target_muscles[:start]