Through-checked baggage

Bags tagged at origin to the final destination across connections — standard within one ticket, discretionary across separate tickets even between partners, and rechecked after customs at certain entry points regardless (the United States notably). The premium-cabin relevance is the connection math: a transfer that works for you must also work for your bags, and an itinerary we build accounts for where they must be collected and rechecked, so the surprise happens to neither of you.