Spent most of today improving behavior when a sync or merge is interrupted in direct mode. It was possible for an interrupt at the wrong time to leave the merge committed, but the work tree not yet updated. And then the next sync would make a commit that reverted the merged changes!
To fix this I had to avoid making any merge commit or indeed updating the index until after the work tree is updated. It looked intractable for a while; I'm still surprised I eventually succeeded.