feat: pipe.broadcast cross-scope push + collect reads exposed

modules/aspects/batteries/home-manager.nix

@@ -6,18 +6,20 @@
   ...
 }:
 let
+  # Where a home-manager user's config nests inside the enclosing host config.
+  # Single source of truth for both the forward delivery target and the
+  # den.classes.homeManager.hostPath the pipe layer resolves producers against.
+  userHostPath = userName: [
+    "home-manager"
+    "users"
+    userName
+  ];
   result = den.lib.home-env.makeHomeEnv {
     className = "homeManager";
     ctxName = "hm";
     optionPath = "home-manager";
     getModule = { host, ... }: inputs.home-manager."${host.class}Modules".home-manager;
-    forwardPathFn =
-      { user, ... }:
-      [
-        "home-manager"
-        "users"
-        user.userName
-      ];
+    forwardPathFn = { user, ... }: userHostPath user.userName;
     schemaIncludes = config.den.schema.hm-host.includes or [ ];
   };
 
@@ -29,4 +31,7 @@ in
   den.schema.user.includes = [ result.userDetect ];
 
   den.classes.homeManager.description = "Home Manager user environment";
+  # home-manager nests under its host; a member reaches the host config via osConfig.
+  den.classes.homeManager.parentPath = userHostPath;
+  den.classes.homeManager.parentArg = "osConfig";
 }

modules/options.nix

@@ -32,6 +32,28 @@ let
         type = lib.types.nullOr lib.types.raw;
         default = null;
       };
+      options.parentPath = lib.mkOption {
+        description = ''
+          For a class whose members nest inside an enclosing config-owner (e.g.
+          home-manager inside a host), a function `name -> path` locating a named
+          member within that owner's config — the same route the class's content
+          is delivered to. The pipe layer uses it to resolve a producer's config
+          at its producing class + scope. null for root classes that own a
+          top-level config (nixos, darwin, terranix, …).
+        '';
+        type = lib.types.nullOr lib.types.raw;
+        default = null;
+      };
+      options.parentArg = lib.mkOption {
+        description = ''
+          For a nested class, the module argument by which a member reaches the
+          enclosing config-owner (home-manager exposes the host config as
+          `osConfig`). The pipe layer hands a deferred config-thunk the owner
+          config under this name. null for root classes.
+        '';
+        type = lib.types.nullOr lib.types.str;
+        default = null;
+      };
     }
   );