- Pin the object-storage trait signatures (GitRefs.list_refs/apply_updates,
GitPackGen.generate/common_haves, GitPackIngest.prepare) — the A-2
amendment's unfinished half (review 001 pinned only the registry pair)
- repo parameter is &RepoRecord (record carries storage_root; no handle
type, no second lookup)
- Shared seam types pinned: RefLine (unborn-symref shape for the N-5
rider), RefUpdate, RefOutcome, PreparedPush, PushOptions
- StorageError for traits 3-5; RegistryError re-scoped to the registry
family (the 'every failure the trait family can produce' claim corrected)
- backend.md: pinned-signatures mirror section, concurrency-model
ownership bridge, boxed-stream parameter-ownership rule
Verification: cargo doc/test/clippy/fmt clean (docs-only change)
