Function reachable_objects 

pub fn reachable_objects(
    store: &ObjectStore,
    root: &Hash,
) -> Result<BTreeSet<Hash>, StoreError>

Collect every object reachable from commit root — the full closure needed to reconstruct the commit on a fresh store. Walks, in order:

1. root commit → its tree_hash + every parent.
2. each tree → every entry’s object_hash (blob / tree / chunked-blob).
3. nested trees → recurse.
4. chunked-blob manifests → every chunks[i] hash.

Deltas are not produced by any path the push code drives, and remix objects are walked like commits (tree + parents) per SPEC-OBJECTS §6.

Returns a BTreeSet so iteration order is deterministic — the push code uses that to build reproducible packfiles. Deduplication happens naturally via the set.

Errors

• StoreError::ObjectNotFound if root itself is missing from the store. Missing referenced objects (e.g. a tree listing a blob that got pruned) are a harder failure and propagate via the same variant — callers pushing partial repos should fix their store before pushing.
• Other StoreError variants propagate as-is.