Problem

The pack reader has scaffolding for REF_DELTA but does not fully resolve them. Thin packs generated by git fetch or git push use REF_DELTA entries referencing objects the receiver already has. Without resolution, these packs fail to import.

Impact

• Real-world clone/fetch interop is broken for thin packs
• Limits usefulness as a git server receiving pushes from standard git clients

Acceptance Criteria

• REF_DELTA objects resolved against the local object store
• Thin packs from git push are correctly imported
• Thin packs from git fetch are correctly consumed
• Interop test: git clone → modify → git push round-trip works
• Error handling for missing base objects returns clear error