Add guess_freeze_seed (default True) threaded refine_v2 -> _v2_pack_batch -> _v2_pack_guess_ladder and the Studio refine_v2 call. Frozen = every rung shares one seed (only conditioning strength varies; cleanest for learning). Off = distinct seed per rung (varied compositions too). New "Freeze seed" toggle in the Interactive Guessing config; persisted on Arm. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>