Re: [PATCH v2 13/17] refs/reftable: fix consistency checks with worktrees

> The ref consistency checks are driven via `cmd_refs_verify()`. That
> function loops through all worktrees (including the main worktree) and
> then checks the ref store for each of them individually. It follows that
> the backend is expected to only verify refs that belong to the specified
> worktree.
>
> While the "files" backend handles this correctly, the "reftable" backend
> doesn't. In fact, it completely ignores the passed worktree and instead
> verifies refs of _all_ worktrees. The consequence is that we'll end up
> every ref store N times, where N is the number of worktrees.
>
> Or rather, that would be the case if we actually iterated through the
> worktree reftable stacks correctly. But we use `strmap_for_each_entry()`
> to iterate through the stacks, but the map is in fact not even properly
> populated. So instead of checking stacks N^2 times, we actually only end
> up checking the reftable stack of the main worktree.
>
> Fix this bug by only verifying the stack of the passed-in worktree and
> constructing the backends via `backend_for_worktree()`.
>