The fold added in #131679 runs `git gc --auto`, which on a large partial
clone is a full repack: a 9.6 GB checkout with 463 packs sat in it for
20 minutes per update, got killed at the cap, and started over on the
next update without ever finishing. It also never freed disk (on-demand
packs are kept, only merged). Turn it off until a bounded, progressive
cleanup replaces it.
The partial-clone keys that stop git writing a commit-graph (#127711)
stay: settle_partial_clone_maintenance re-applies them every update and
leaves full clones alone, and git's own automatic gc still folds packs.
1fd75357e9