Before re-running a cell whose scripts write fixed output paths, rename the old outputs and resume state

Rerunning an experiment cell (same name) with a changed bar: the eval script writes heldout_<cell>.json, the status file and the warm-resume folder resume/<cell>/ all have fixed names. If left in place, (1) the launcher silently warm-starts from the old resume folder instead of a cold start, (2) the new eval overwrites the old result, and (3) a watcher reading the status file sees the old 'DONE' line and fires at once. Move each one to a dated name (resume_prev/<cell>_<date>, heldout_<cell>.<tag>.json, <status>.<tag>) first, then dry-run the launcher and confirm resume_offset=0 and the new bar before the real launch.