Upgrade Nix to 2.32

I did this in Nix for this purpose, but didn't get around to actually
taking advantage of it here, until now.

flake.lock

@@ -36,16 +36,16 @@
     },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1764020296,
+        "lastModified": 1759652726,
-        "narHash": "sha256-6zddwDs2n+n01l+1TG6PlyokDdXzu/oBmEejcH5L5+A=",
+        "narHash": "sha256-2VjnimOYDRb3DZHyQ2WH2KCouFqYm9h0Rr007Al/WSA=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "a320ce8e6e2cc6b4397eef214d202a50a4583829",
+        "rev": "06b2985f0cc9eb4318bf607168f4b15af1e5e81d",
         "type": "github"
       },
       "original": {
         "owner": "NixOS",
-        "ref": "nixos-25.11-small",
+        "ref": "nixos-25.05-small",
         "repo": "nixpkgs",
         "type": "github"
       }

flake.nix

@@ -1,7 +1,7 @@
 {
   description = "A Nix-based continuous build system";
 
-  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-25.11-small";
+  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-25.05-small";
 
   inputs.nix = {
     url = "github:NixOS/nix/2.32-maintenance";
@@ -59,7 +59,7 @@
 
         manual = forEachSystem (system: let
           pkgs = nixpkgs.legacyPackages.${system};
-          hydra = self.packages.${pkgs.stdenv.hostPlatform.system}.hydra;
+          hydra = self.packages.${pkgs.hostPlatform.system}.hydra;
         in
           pkgs.runCommand "hydra-manual-${hydra.version}" { }
             ''

nixos-modules/default.nix

@@ -4,7 +4,7 @@
   hydra = { pkgs, lib,... }: {
     _file = ./default.nix;
     imports = [ ./hydra.nix ];
-    services.hydra-dev.package = lib.mkDefault self.packages.${pkgs.stdenv.hostPlatform.system}.hydra;
+    services.hydra-dev.package = lib.mkDefault self.packages.${pkgs.hostPlatform.system}.hydra;
   };
 
   hydraTest = { pkgs, ... }: {

package.nix

@@ -31,7 +31,7 @@
 , perl
 , pixz
 , boost
-, postgresql_17
+, postgresql_13
 , nlohmann_json
 , prometheus-cpp
 
@@ -192,7 +192,7 @@ stdenv.mkDerivation (finalAttrs: {
     subversion
     breezy
     openldap
-    postgresql_17
+    postgresql_13
     pixz
     nix-eval-jobs
   ];

src/hydra-queue-runner/build-remote.cc

@@ -104,9 +104,9 @@ static void copyClosureTo(
     std::unique_lock<std::timed_mutex> sendLock(conn.machine->state->sendLock,
         std::chrono::seconds(600));
 
-    conn.to << ServeProto::Command::ImportPaths;
+    conn.importPaths(destStore, [&](Sink & sink) {
-    exportPaths(destStore, missing, conn.to);
+        exportPaths(destStore, missing, sink);
-    conn.to.flush();
+    });
 
     if (readInt(conn.from) != 1)
         throw Error("remote machine failed to import closure");
@@ -301,12 +301,11 @@ static void copyPathFromRemote(
               lambda function only gets executed if someone tries to read
               from source2, we will send the command from here rather
               than outside the lambda. */
-          conn.to << ServeProto::Command::DumpStorePath << localStore.printStorePath(info.path);
+          conn.narFromPath(localStore, info.path, [&](Source & source) {
-          conn.to.flush();
+              TeeSource tee(source, sink);
-
-          TeeSource tee(conn.from, sink);
               extractNarData(tee, localStore.printStorePath(info.path), narMembers);
           });
+      });
 
       destStore.addToStore(info, *source2, NoRepair, NoCheckSigs);
 }

src/lib/Hydra/Plugin/GithubRefs.pm

@@ -18,8 +18,9 @@ tags) from GitHub following a certain naming scheme
 
 =head1 DESCRIPTION
 
-This plugin reads the list of branches or tags using GitHub's REST API. This
+This plugin reads the list of branches or tags using GitHub's REST API. The name
-list is stored in the nix-store and used as an input to declarative jobsets.
+of the reference must follow a particular prefix. This list is stored in the
+nix-store and used as an input to declarative jobsets.
 
 =head1 CONFIGURATION
 
@@ -33,7 +34,7 @@ The declarative project C<spec.json> file must contains an input such as
 
    "pulls": {
      "type": "github_refs",
-     "value": "[owner] [repo] [type] - [prefix]",
+     "value": "[owner] [repo] heads|tags - [prefix]",
      "emailresponsible": false
    }
 
@@ -41,11 +42,12 @@ In the above snippet, C<[owner]> is the repository owner and C<[repo]> is the
 repository name. Also note a literal C<->, which is placed there for the future
 use.
 
-C<[type]> is the type of ref to list. Typical values are "heads", "tags", and
+C<heads|tags> denotes that one of these two is allowed, that is, the third
-"pull". "." will include all types.
+position should hold either the C<heads> or the C<tags> keyword. In case of the former, the plugin
+will fetch all branches, while in case of the latter, it will fetch the tags.
 
 C<prefix> denotes the prefix the reference name must start with, in order to be
-included. "." will include all references.
+included.
 
 For example, C<"value": "nixos hydra heads - release/"> refers to
 L<https://github.com/nixos/hydra> repository, and will fetch all branches that
@@ -100,6 +102,8 @@ sub fetchInput {
     return undef if $input_type ne "github_refs";
 
     my ($owner, $repo, $type, $fut, $prefix) = split ' ', $value;
+    die "type field is neither 'heads' nor 'tags', but '$type'"
+        unless $type eq 'heads' or $type eq 'tags';
 
     my $auth = $self->{config}->{github_authorization}->{$owner};
     my $githubEndpoint = $self->{config}->{github_endpoint} // "https://api.github.com";