extract_printable_objects_from_3mf() has accepted a plate_number since it was
written and no caller ever passed one, so it took root.find(".//plate") — the
first plate in the file. Passing one would not have helped either: the lookup
was .//plate[@plate_idx='N'], a predicate on an attribute neither Bambu Studio
nor OrcaSlicer writes. The index lives in a <metadata key="index"> child, as
threemf_tools and filament_requirements already read it, so the selector never
matched and fell back to plate 1 regardless.
On an all-plates .gcode.3mf that meant Skip Objects offered the wrong plate's
objects, with that plate's marker positions drawn over the correct plate's
thumbnail (/cover resolves the plate properly via resolve_plate_id, the object
list did not). The reporter printed a one-object plate and was shown the four
copies from another plate of the same file.
Select the plate on its index metadata, and pass resolve_plate_id(state) at all
three call sites so the list and the thumbnail share one resolver. Also stop
peek_plate_index_in_3mf() reporting plate 1 for a multi-plate file: it backs the
running one, so an all-plates upload printing plate 2+ lost its archive entirely.
