The preview brim, the placement margin and the pre-generation validation
warning each decided on their own whether the tower has a Type2 cone
base, reading the wall type and cone angle three different ways. The
preview's read cast the preset's enum to ConfigOptionEnum<T>, which a
preset-shaped config never holds, so the cone base was never previewed.
estimate_wipe_tower_first_layer_outline now answers that question once,
beside the footprint estimate, from the config and the resolved planner;
all three sites take the outline from it. The libslic3r case reads the
outline off a preset-shaped config, where the old cast came back empty.