def dedupe_preserve_order(items: list[int]) -> list[int]:
    """Remove duplicates while preserving first occurrence order."""
    seen = set()
    out = []
    for item in items:
        # BUG: keeps last occurrence logic effectively by replacing list.
        if item in seen:
            out = [x for x in out if x != item]
        seen.add(item)
        out.append(item)
    return out