{
  # Exposes `apps.<system>` entries that point at small runnable programs.
  description = "A minimal flake apps example";

  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
  };

  outputs =
    { self, nixpkgs, ... }:
    let
      system = "x86_64-linux";
      pkgs = import nixpkgs { inherit system; };

      releaseName = "search-index-2026-04";
      releasePlan = [
        {
          stage = "staging";
          percentage = 10;
          owner = "team-search";
          gates = [
            "smoke-tests"
            "error-budget"
          ];
        }
        {
          stage = "canary";
          percentage = 35;
          owner = "team-search";
          gates = [
            "dashboard-review"
            "support-readiness"
          ];
        }
        {
          stage = "production";
          percentage = 100;
          owner = "team-search";
          gates = [
            "canary-slo"
            "stakeholder-signoff"
          ];
        }
      ];

      renderWave =
        wave:
        "${wave.stage}: ${toString wave.percentage}% owned by ${wave.owner}; gates: ${builtins.concatStringsSep ", " wave.gates}";

      reportText = builtins.concatStringsSep "\n" (
        [
          "release: ${releaseName}"
          "waves:"
        ]
        ++ map renderWave releasePlan
      );

      nextWave = builtins.elemAt releasePlan 1;

      reportPackage = pkgs.writeShellApplication {
        name = "show-rollout-report";
        text = ''
          cat <<'EOF'
          ${reportText}
          EOF
        '';
      };

      promotePackage = pkgs.writeShellApplication {
        name = "suggest-next-promotion";
        text = ''
          echo "next wave: ${nextWave.stage} (${toString nextWave.percentage}%) after ${builtins.concatStringsSep " and " nextWave.gates}"
        '';
      };
    in
    {
      packages.${system} = {
        default = reportPackage;
        report = reportPackage;
        promote = promotePackage;
      };

      apps.${system} = {
        default = {
          type = "app";
          program = "${reportPackage}/bin/show-rollout-report";
          meta.description = "Print the rollout report for a release train.";
        };

        promote = {
          type = "app";
          program = "${promotePackage}/bin/suggest-next-promotion";
          meta.description = "Print the next rollout wave that should be promoted.";
        };
      };

      checks.${system}.apps-run = pkgs.runCommand "flake-apps-run" { } ''
        report="$(${self.apps.${system}.default.program})"
        promote="$(${self.apps.${system}.promote.program})"

        printf '%s\n' "$report" | grep -q '^release: ${releaseName}$'
        printf '%s\n' "$report" | grep -q '^production: 100% owned by team-search; gates: canary-slo, stakeholder-signoff$'

        if [ "$promote" != "next wave: canary (35%) after dashboard-review and support-readiness" ]; then
          echo "unexpected promotion output: $promote" >&2
          exit 1
        fi

        echo ok > "$out"
      '';
    };
}