Function resolve_tree 

pub fn resolve_tree(
    repo: &Path,
    ref_name: &str,
) -> Result<Option<String>, SyncError>

Resolves a ref to its tree SHA, or None if the ref does not exist.

Part of the git-ref sync foundation’s public API. Retained for the global store and daemon wiring in later phases; the per-repo command resolves commits via resolve_ref and reads trees via read_tree, so the binary does not yet call this directly.