import re


def parse_handles(raw: str) -> list[str]:
    """"DBUCentral, @DBUcentralforum" -> ["@DBUCentral", "@DBUcentralforum"] (no duplicates, case-insensitive)."""
    seen, out = set(), []
    for part in re.split(r"[,\s]+", raw or ""):
        handle = part.strip().lstrip("@")
        if handle and handle.lower() not in seen:
            seen.add(handle.lower())
            out.append("@" + handle)
    return out