With single_extruder_multi_material and purge_in_prime_tower, the flush
matrix replaces the prime volume and its average is non-zero for one
filament, so the estimate reports a tower. normalize_fdm_2 clears the tower
for that same plate, so none is printed: the estimate answers how big a
tower is, never whether there is one, and a caller reading a non-zero depth
as "a tower is printed" reserves space for, or blocks on, a phantom. The
test asserts that disagreement directly.
Type1 is the exception in the same case, because it decides from its
per-filament purge list and a lone filament is never changed to. The scene
reads the same estimate either way. Type2 is the default for every non-Bambu
printer, and so for every IDEX/IQEX one.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
