horizon_client::packs::SelectionModel ports PackRepository's selection and
PackSelectionModel (default positions, fixed and required packs, moving up
and down, commit), and the pack screen uses it. The new pack_selection
harness drives vanilla's model and Horizon's through 4,000 random action
sequences; every state matches.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Ludovic Marie