ww: select build action from package declaration

test/wcc/data/paramshadowmod/pos_crossmod.ww

@@ -6,7 +6,7 @@
 // own module — must NOT trip crossmod's param, even though a sibling
 // module in the same bundle imports that leaf. Build + run; exit = 2.
 
-package paramshadowmod;
+package main;
 
 import shadowmod;
 import crossmod;