The AMS remain% delta path charged every tray with a delta, not just
trays involved in the print. Swapping a spool in an UNUSED slot mid-
print made the slot report remain=0 (fresh spool, no tag), versus a
print-start snapshot of 100%, so the originally-assigned spool got
charged the full 1000g.
Build print_used_keys from ams_mapping, tray_change_log, and
tray_now_at_start, and skip fallback for trays not in that set.
Legacy "scan every tray" behavior preserved when none of the three
signals are present.
maziggy
4b7df9f30b