Decided 2026-08-29: the arm64 Qt build only works on ubuntu-24.04-arm (aqt's arm64 host tools segfault on 22.04-arm), so the arm64 desktop app requires glibc 2.39; qbzd keeps building on 22.04-arm at 2.35 so a trimmed Pi OS bookworm image stays a valid target. The floor gate asserts per arch instead of warning; README states both floors. cc