Problem

No support for git object alternates (objects/info/alternates). Each repository must contain its own copy of every object, even when repos share history (forks, related projects).

Impact

• Fork-heavy hosting wastes storage (each fork duplicates the entire object store)
• Cannot implement efficient fork networks
• Monorepo sharding patterns unsupported

Acceptance Criteria

• Repos can reference alternate object stores for reads
• Object resolution checks local store first, then alternates
• Alternates are configurable per-repo
• Works with filesystem backend (S3 support optional)
• GC is alternate-aware (doesn’t prune objects reachable via alternates)
• Tests covering read-through, missing objects, circular alternate chains