BambuStudio encodes virtual tray IDs (254/255) as -1 in the flat
ams_mapping array — a convention already documented in
bambu_mqtt.py:start_print(). The spoolman tracking helper was treating
-1 as "unmapped, use position-based default", which mapped slot_id=1
to AMS tray 0 and credited external-spool prints to whatever Spoolman
spool happened to be linked to AMS slot 0. The reporter's TPU prints
on an H2S were credited to a PLA spool for ~49g over 4 prints before
being noticed (regression of #853).
When slot_to_tray[slot_id-1] == -1 and ams_trays contains 254/255,
return the external tray ID directly. Prefers 254 over 255 (matches
single-nozzle tray_now reporting + the vir_slot id=255->254 remap in
bambu_mqtt.py:864). Legacy fall-through preserved for callers that
don't pass ams_trays.
Root cause investigation and patch by @ojimpo.
maziggy
6fe00adb23