Make 'nix run' spin up the whole stack in one command

flake.nix

@@ -7,27 +7,36 @@
     let
       systems = [ "x86_64-linux" "aarch64-linux" "x86_64-darwin" "aarch64-darwin" ];
       forAll = f: nixpkgs.lib.genAttrs systems (system: f nixpkgs.legacyPackages.${system});
+      toolchain = pkgs:
+        let php = pkgs.php83; in
+        [ php php.packages.composer pkgs.mariadb pkgs.nodejs_22 ];
     in
     {
-      devShells = forAll (pkgs:
-        let
-          php = pkgs.php83;
-        in
-        {
-          default = pkgs.mkShell {
-            packages = [
-              php
-              php.packages.composer
-              pkgs.mariadb
-              pkgs.nodejs_22
-            ];
+      devShells = forAll (pkgs: {
+        default = pkgs.mkShell {
+          packages = toolchain pkgs;
+          shellHook = ''
+            export DEV_ROOT="$PWD"
+            export PATH="$DEV_ROOT/dev:$PATH"
+            echo "think-greaterchiangmai dev shell — run 'dev help'"
+          '';
+        };
+      });
 
-            shellHook = ''
-              export DEV_ROOT="$PWD"
-              export PATH="$DEV_ROOT/dev:$PATH"
-              echo "think-greaterchiangmai dev shell — run 'dev help'"
+      # `nix run` = `dev up` with the toolchain on PATH, no `nix develop` needed.
+      # Runs the checked-out dev/dev (not a store copy) so state lands in the working tree.
+      apps = forAll (pkgs: {
+        default = {
+          type = "app";
+          program = toString (pkgs.writeShellApplication {
+            name = "dev";
+            runtimeInputs = toolchain pkgs;
+            text = ''
+              [ -x "$PWD/dev/dev" ] || { echo "run from the repo root (dev/dev not found in $PWD)" >&2; exit 1; }
+              DEV_ROOT="$PWD" exec "$PWD/dev/dev" "''${@:-up}"
             '';
-          };
-        });
+          }) + "/bin/dev";
+        };
+      });
     };
 }