imp: integrate devshell & nixago tightly

cells/std/lib/default.nix

@@ -4,18 +4,60 @@
 }: let
   nixpkgs = inputs.nixpkgs;
 in {
-  inherit (inputs.devshell.legacyPackages) mkShell;
+  mkShell = configuration: let
+    nixagoModule = {
+      config,
+      lib,
+      ...
+    }:
+      with lib; let
+        cfg = config.devshell;
+      in {
+        options.nixago = mkOption {
+          type = types.listOf types.attrs;
+          default = [];
+          apply = x: x.passthru;
+          description = "List of `std` Nixago pebbles to load";
+        };
+
+        config.devshell = mkIf (cfg.nixago != []) {
+          startup.nixago-setup-hook = stringBefore ["motd"] inputs.nixago.lib.makeAll cfg.nixago;
+          packages = builtins.concatMap (o: o.packages) cfg.nixago;
+          commands = builtins.concatMap (o: o.commands) cfg.nixago;
+        };
+      };
+  in
+    inputs.devshell.legacyPackages.mkShell {
+      imports = [configuration nixagoModule];
+    };
+
   mkNixago = configuration:
     (inputs.nixago.lib.make configuration)
     // {
-      # transparently extend config data with a functor
-      __functor = _: extra: (inputs.nixago.lib.make (configuration
+      # passthru configuration
+      passthru =
+        configuration
         // {
-          configData = inputs.data-merge.merge configuration.configData extra;
-        }));
-      # implement a minimal numtide/devshell forward contract
-      packages = configuration.packages or [];
-      commands = configuration.commands or [];
+          # implement a minimal numtide/devshell forward contract
+          packages = configuration.packages or [];
+          commands = configuration.commands or [];
+        };
+
+      # transparently extend config data with a functor
+      __functor = self: {
+        configData ? {},
+        packages ? [],
+        commands ? [],
+      }: let
+        newSelf =
+          self.passthru
+          // {
+            configData = inputs.data-merge.merge self.passthru.configData configData;
+            packages = self.passthru.packages ++ packages;
+            commands = self.passthru.commands ++ commands;
+          };
+      in
+        inputs.nixago.lib.make (newSelf // {passthru = newSelf;});
     };
 
   fromMakesWith = inputs': let

cells/std/lib/mkNixago.md

@@ -2,4 +2,21 @@
 
 This is a transparent convenience proxy for [`nix-community/nixago`'s][nixago] `lib.${system}.make` function.
 
+It is enriched with a forward contract towards `std` enriched `mkShell` implementation.
+
+In order to define [`numtide/devshell`'s][numtide-devshell] `commands` & `packages` alongside the Nixago pebble,
+just add the following attrset to the Nixago spec. It will be picked up automatically by `mkShell` when that pebble
+is used inside its `config.nixago`-option.
+
+```nix
+{ inputs, cell }: {
+  foo = inputs.std.std.lib.mkNixago {
+    /* ... */
+    packages = [ /* ... */ ];
+    commands = [ /* ... */ ];
+  };
+}
+```
+
 [nixago]: https://github.com/nix-community/nixago
+[numtide-devshell]: https://github.com/numtide/devshell

cells/std/lib/mkShell.md

@@ -2,4 +2,20 @@
 
 This is a transparent convenience proxy for [`numtide/devshell`'s][numtide-devshell] `mkShell` function.
 
+It is enriched with a tight integration for `std` [Nixago][nixago] pebbles:
+
+```nix
+{ inputs, cell}: {
+  default = inputs.std.std.lib.mkShell {
+    /* ... */
+    nixago = [
+      cell.nixago.foo
+      cell.nixago.bar
+      cell.nixago.quz
+    ];
+  };
+}
+```
+
+[nixago]: https://github.com/nix-community/nixago
 [numtide-devshell]: https://github.com/numtide/devshell