Repos that accumulate many small packs get slow object lookups. A multi-pack index provides a single sorted OID → (pack, offset) table across all packs.

Scope

• Reader of the multi-pack-index format.
• Writer that generates one from a directory of packs.
• ObjectResolver prefers the midx over per-pack indices.
• Invalidation hook when packs are added/removed (repack, receive-pack).

Acceptance

• Object-lookup latency on a 50-pack fixture drops ≥5x with midx.
• Stays consistent with per-pack idx on random round-trips.