update grafting logic.

pkgs/default.nix

 { # host package set (unused except for fetching nixpkgs)
-  hostPkgs        ? import <nixpkgs> {}
+  hostPkgs         ? import <nixpkgs> {}
 
 , # versioned nixpkgs
-  pkgs            ? import (hostPkgs.nix-update-source.fetch ./pkgs.json).src {}
+  pkgs             ? import (hostPkgs.nix-update-source.fetch ./pkgs.json).src {}
 
 , # versioned nixpkgs-older version for zmcat
-  pkgs-old        ? import (hostPkgs.nix-update-source.fetch ./pkgs-old.json).src {}
+  pkgs-old         ? import (hostPkgs.nix-update-source.fetch ./pkgs-old.json).src {}
 
 , # fetcher alias for the remaining arguments
-  fetched         ? s: (pkgs.nix-update-source.fetch s).src
+  fetched          ? s: (pkgs.nix-update-source.fetch s).src
 
 , #source overrides: core nrm components
-  aml-src         ? fetched aml/pin.json
-, libnrm-src      ? fetched libnrm/pin.json
-, nrm-src         ? fetched nrm/pin.json
-, containers-src  ? fetched containers/pin.json
+  aml-src          ? fetched aml/pin.json
+, libnrm-src       ? fetched libnrm/pin.json
+, nrm-src          ? fetched nrm/pin.json
+, containers-src   ? fetched containers/pin.json
 
 , #source overrides: applications
-  amg-src         ? fetched amg/pin.json
-, qmcpack-src     ? fetched qmcpack/pin.json
-, openmc-src      ? fetched openmc/pin.json
-, stream-src      ? fetched stream/pin.json
-, lammps-src      ? fetched lammps/pin.json
+  amg-src          ? fetched amg/pin.json
+, qmcpack-src      ? fetched qmcpack/pin.json
+, openmc-src       ? fetched openmc/pin.json
+, stream-src       ? fetched stream/pin.json
+, lammps-src       ? fetched lammps/pin.json
 
 , #source overrides: tooling
   argotk-src       ? builtins.fetchGit {inherit (fetched argotk/pin.json) url rev;}
@@ -30,10 +30,10 @@
 , experiments-src  ? fetched experiments/pin.json
 
 , #used for hardware experiments.
-  sudoPath ? null
+  sudoPath         ? null
 
-, #whether to rebuild apps when libnrm changes.
-  rebuildApps ? true
+, #whether to graft apps on libnrm.
+  graftLibnrm      ? false
 }:
 let
   callPackage = pkgs.lib.callPackageWith (pkgs // argopkgs);
@@ -60,11 +60,13 @@ let
         src = src;
         libnrm = libnrm-pinned;
       };
-    in if !rebuildApps then drv else pkgs.replaceDependency {
-      drv = drv;
-      oldDependency = libnrm-pinned;
-      newDependency = libnrm;
-    };
+      rebuilt = drv.override {libnrm =libnrm;};
+      grafted = pkgs.replaceDependency {
+        drv = drv;
+        oldDependency = libnrm-pinned;
+        newDependency = libnrm;
+      };
+    in if graftLibnrm then grafted else rebuilt;
     amg          = repLibnrm ./amg     amg-src     {};
     qmcpack      = repLibnrm ./qmcpack qmcpack-src {};
     openmc       = repLibnrm ./openmc  openmc-src  {};
@@ -273,33 +275,3 @@ let
   };
 # re-exporting a full nixpkgs-like package set
 in pkgs // argopkgs
-
-
-
-
-    #jupyter =
-      #let
-        #jupyter = import (fetched jupyter/pin.json) {};
-      #in
-       #(jupyter.jupyterlabWith {
-          #kernels = [
-            #(jupyter.kernels.juniperWith {
-              #name = "analysis";
-              #packages = p: with p; [ ggplot2
-                  #pkgs.which
-                  #docopt
-                  #purrr
-                  #knitr
-                  #cowplot
-                  #plotly
-                  #lubridate
-                  #dplyr
-                  #ggplot2
-                  #xtable
-                  #ggthemes
-                  #data_table
-              #];
-            #})
-          #];
-         #}).env;
-