Problem

• Manual post pipelines (post.detect_soma/reroot after skeletonization) remapped ntype using the old permutation but always forced the new index 0 to 1 without clearing the old soma label. When the soma moved, the previous root kept ntype==1, producing two soma nodes intermittently. The full automatic pipeline didn’t hit this because ntype is None during its post steps.

Fix

• After remapping ntype, explicitly clear any duplicate soma labels so only index 0 remains 1.
• When rerooting with set_soma_ntype=True, also strip any extra ntype==1 outside the new root.
• Added regression tests to ensure reroot and detect_soma leave exactly one soma label.