Serving a clone via upload-pack's delta-compression re-reads pack objects thousands of times. Commit 76bb55d made pack reads lazy to avoid RAM buffering; this causes each access to issue a fresh S3 GetObject, making real-repo clones never finish. Implement PackCache: immutable pack-dir files (.pack/.idx/.rev) download once to a local temp file (LRU-bounded by -pack-cache-bytes, default 2GB) and all reads serve from local disk. Results on real Tigris bucket: - objgit (318 objects, 200KB pack): 8500+ GetObjects → 10, 7s - kefka (197 commits, 19.6MB pack): hang → 14s, full clone The cache is wired into OpenFile and shared across Chroot children like the listing cache. Add flags: -pack-cache-bytes, -pack-cache-dir. See docs/plans/pack-temp-file-cache.md for design. Assisted-by: Claude Opus 4.8 via claude.ai Signed-off-by: Xe Iaso <me@xeiaso.net>