Created Started Finished
Update the flake inputs Bottom of a three-PR stack. `nix flake update` across every input: nixpkgs (nixos-26.05, 2026-10-07), nixpkgs-25_11, horizon-advance, pre-commit-hooks, sydtest, validity, opt-env-conf, safe-coloured-text and fast-myers-diff. It also drops the `nixos-25.05` backward-compatibility check. sydtest no longer builds on the GHC that release ships — `sydtest-mutation-runtime`'s `Test/Syd/Mutation/AugmentedManifest.hs` uses `foldl'` without importing it, which only compiles against base >= 4.20 where Prelude re-exports it — and 26.05 is the release this has to work on. `nixos-25.11` still works, so it stays. `nix flake check` passes.