w6c+selfhost: cross-module same-leaf type disambiguation via Sym.mod

test/wcc/data/modcollision/neg.ww

@@ -0,0 +1,19 @@
+// Negative case: declare `b: mod1.stream` then access a mod2-only
+// field. With the mod-tagged scope lookup `b` resolves to mod1.stream
+// (fields a, b), so the field access `b.c` must be a compile-time
+// error rather than silently binding to mod2.stream and succeeding.
+//
+// No cross-module call is made: a missing mod1.make would itself
+// trigger a link-time error that could mask the field-resolution
+// error this test is actually pinning. `let b: mod1.stream;` is
+// enough — we read b.c before initializing it, which is fine because
+// the field-resolution error fires at check, long before any reach
+// analysis or codegen runs.
+
+use mod1;
+use mod2;
+
+fn main() i32 = {
+	let b: mod1.stream;
+	return b.c;	// mod1.stream has no `c`; expect a compile error.
+};