ww: add file-scoped import aliases

selfhost/cmd/wcc/cgenutil.ww

@@ -586,8 +586,15 @@ fn pushargsrev(c: *cgen, arg: *syntax.node, param: *syntax.node, memphase: bool,
 					};
 					if (!aistagged) {
 						widensz = slotsize(c, ptype);
-						let tagged: *syntax.node = resolvetagged(c, ptype);
-						let t: i32 = taggedvariantindex(c, tagged, arg);
+						// The parameter may come from an imported signature whose
+						// qualifier is owned by that interface source, not by the
+						// caller currently being emitted.  The checker has already
+						// resolved and stamped its canonical type; use that identity
+						// directly instead of re-resolving source-local alias text in
+						// the caller's scope.  Mirrors cstage's Type-keyed
+						// cg_tag_for_variant path.
+						let t: i32 = taggedvariantindext(c,
+							ptype.type_: *syntax.tinfo, arg);
 						// tagged→tagged subset sources synthesize
 						// no scalar tag here (the widen store
 						// remaps); only a CONCRETE source with no