make-sandboxed: preserve meta.mainProgram

modules/programs/make-sandboxed.nix

@@ -113,9 +113,12 @@ let
 
   # there are certain `meta` fields we care to preserve from the original package (priority),
   # and others we *can't* preserve (outputsToInstall).
-  extractMeta = pkg: if (pkg ? meta) && (pkg.meta ? priority) then {
-    inherit (pkg.meta) priority;
-  } else {};
+  extractMeta = pkg: let
+    meta = pkg.meta or {};
+  in
+    (lib.optionalAttrs (meta ? priority) { inherit (meta) priority; })
+    // (lib.optionalAttrs (meta ? mainProgram) { inherit (meta) mainProgram; })
+  ;
 
   # helper used for `wrapperType == "wrappedDerivation"` which simply symlinks all a package's binaries into a new derivation
   symlinkBinaries = pkgName: package: (runCommandLocal "${pkgName}-bin-only" {} ''