libstore: fix race condition when creating state directories (backport #13368)#13637
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Running (parallel?) nix in nix can lead to multiple instances trying to create the state directories and failing on the
createSymlinkstep, because the link already exists.replaceSymlinkis already idempotent, so let's use that.Resolves #2706
I only see this race appearing in Nixpkgs' CI right now, for example https://github.com/NixOS/nixpkgs/actions/runs/15426171510/job/43413501065. It only happens very infrequently. I tried reproducing locally, by just running
nix-build ci -A nixpkgs-vetin a loop, but didn't succeed, so far. I'm running Lix locally, but that shouldn't make a difference, the relevant code is the same. I assume I can't reproduce, because I'd need to start from an empty cache, but I'm not sure.Add 👍 to pull requests you find important.
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This is an automatic backport of pull request #13368 done by [Mergify](https://mergify.com).