Print::apply() decided the shrinkage compensation from the existing PrintObjects and their regions. On the first apply() they do not exist yet, so the first slice was not scaled. The CLI calls apply() only once, so filament_shrink and filament_shrinkage_compensation_z had no effect there.
The compensation is now decided before the PrintObjects are built, from the filaments the model uses, and stored in Print. When the filaments have different shrinkage values, every filament assigned to a feature, height range, modifier, support, tool change or the wipe tower counts, even if it does not end up printing. If they disagree, compensation stays off with the existing warning.
The build height check in Print::validate() compared object layers that already include the Z shrinkage compensation against printable_height divided by that compensation. That counted the compensation twice, so objects that fit were rejected. The check also left out the raft, so an object whose top plus the raft is above printable_height passed validation.
The check now adds object_print_z_min to the top layer and applies the compensation once. The shrinkage message is shown only when the object fits without the compensation. Belt printers apply the compensation to the raw model height, since their height does not come from the layers.
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