Stuck on "sending inputs" with Nix 2.32

> I think this isn't doing good to the queue runner. Builds tend to get stuck on "sending inputs" forever. So we're filling slots by these over time, with the throughput getting lower and lower. > > I see hydra upgraded and nix with it (2.29 -> 2.32), so these would be the primary suspects. _Originally posted by @vcunat in https://github.com/NixOS/infra/issues/858#issuecomment-3419807573_