fetch vale styles in nix, pinned, and drop vale sync

nix/packages/vale-styles.nix

@@ -0,0 +1,40 @@
+{
+  lib,
+  fetchzip,
+  runCommand,
+}:
+
+# The Vale style packages named in `.vale.ini`, fetched at build time and
+# laid out as Vale expects a `StylesPath`: `<out>/<Package>/<rule>.yml`.
+# Each is the release asset `vale sync` would download, pinned to a tag and
+# hash so a lint run makes no network request and every caller sees the
+# same rules. Bumping a style means changing its `tag` and `hash` here.
+let
+  styles = {
+    Microsoft = {
+      tag = "v0.15.1";
+      hash = "sha256-NqH69LL8aKMqyoo5qWi/hFAkYA4WL7OCfTpPwR907vU=";
+    };
+    alex = {
+      tag = "v0.2.3";
+      hash = "sha256-YvNfhjCg437wDMxnOqu9xTKq82KZfQt9HvCpoDfwsL4=";
+    };
+    write-good = {
+      tag = "v0.4.1";
+      hash = "sha256-XhvZtirGg9Vl/i73HMyZpK2iSoQoXv8OS7ckryveIdU=";
+    };
+  };
+
+  fetch =
+    name:
+    { tag, hash }:
+    fetchzip {
+      url = "https://github.com/vale-cli/${name}/releases/download/${tag}/${name}.zip";
+      inherit hash;
+      stripRoot = false;
+    };
+in
+runCommand "vale-styles" { } ''
+  mkdir -p $out
+  ${lib.concatStrings (lib.mapAttrsToList (name: s: "ln -s ${fetch name s} $out/${name}\n") styles)}
+''