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OrcaSlicer/tests/libslic3r
SoftFever c168d0c8db Stop estimating a prime tower for a single used filament (#15760)
# Description

A plate using one filament no longer reserves or draws a prime tower in
the plater just because multiple filament slots are configured. The
shared footprint estimate gated "no tower" on the purge volume being
zero, but on non-Bambu printers with the shipped defaults that volume
comes from the SEMM flush matrix, which reads every configured slot and
stays nonzero even when only one filament is used — so the preview
showed a tower the print could never contain. The estimate now decides
from the filament count alone, with wrapping detection and smooth
timelapse staying the only reasons a single-filament plate keeps a
tower, matching `Print::has_wipe_tower()`. The gate also moved above the
flush-volume scan so the lone-filament path no longer pays for it.

No change to slicing output — toolpath generation already omitted the
tower for a single used filament; this removes the phantom preview,
placement reservation, and validation footprint.

# Screenshots/Recordings/Graphs
Before the fix:


https://github.com/user-attachments/assets/c5b0ea61-127d-408e-bafe-f1f76c58b996

After the fix:


https://github.com/user-attachments/assets/ac6632b3-5d44-4013-aca3-73f6cfd1139c



## Tests

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changes made in this PR.
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Added a shipped-defaults single-filament case to
`tests/libslic3r/test_wipe_tower_estimate.cpp`: it estimates a 5.04
mm-deep tower before the fix and zero depth after. `[WipeTowerEstimate]`
and the fff_print `[WipeTower]` suites pass.

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