anchor.diff:  
       home.activation.linkGeneration = dagEntryAfter ["writeBoundary"] (
         let
  -        pattern = "-home-manager-files/";
  -
           link = pkgs.writeText "link" ''
             newGenFiles="$1"
             shift
  
positive.code:             targetPath="$HOME/$relativePath"
              if [[ -e "$newGenFiles/$relativePath" ]] ; then
                $VERBOSE_ECHO "Checking $targetPath: exists"
              elif [[ ! "$(readlink "$targetPath")" =~ "${pattern}" ]] ; then
                warnEcho "Path '$targetPath' not link into Home Manager generation. Skipping delete."
              else
                $VERBOSE_ECHO "Checking $targetPath: gone (deleting)"
  
negative.code:     # overwrite an existing file.
      home.activation.checkLinkTargets = dagEntryBefore ["writeBoundary"] (
        let
          check = pkgs.writeText "check" ''
            . ${./lib-bash/color-echo.sh}
  
  