git bundle produces a single file containing refs + packfile suitable for offline transfer.

Scope

• Bundle.create(repo, refs, opts) → stream of bundle bytes (supports --all, specific refs, ref+exclude).
• Bundle.unbundle(repo, io, opts) → writes objects + optionally advances refs.
• Support bundle v2 and v3 (prerequisites header).

Acceptance

• Round-trip: bundle a fixture repo, unbundle into an empty repo, diff trees — identical.
• Interop: git bundle verify on our output passes; git clone from our bundle works.