Re: [PATCH v2 0/3] refs: report old OIDs for batched deletions

> The reference-transaction hook receives zero as both the old and new OID
> when branch, tag, fetch, and remote delete refs through refs_delete_refs().
> Those callers already know the values that they selected for deletion.
>
> Teach refs_delete_refs() to accept aligned old OIDs and pass them into the
> transaction. Besides making the hook records useful, this makes the selected
> callers reject concurrent changes instead of deleting values that they did
> not inspect. For branch and tag, this restores the compare-and-delete
> behavior that existed before 8198907795 converted them to batched deletion.
> For pruning, it prevents a stale scan from deleting a ref updated by another
> process.
>
> The values are already available at every updated call site, so the series
> adds no ref reads and retains batched performance.

>
> Changes since v1:
>
>  * Document the conditional deletion behavior and its race protection.
>  * Add tests that update refs from the hook's preparing phase and verify that
>    branch deletion and remote pruning preserve the concurrent update.
>  * Avoid printing deletion status when a non-atomic prune fails.
>  * Use a local string_list_item in refs_delete_refs(), as suggested by
>    Karthik.
>
> Based on maint at e9019fcafe (Git 2.55).