Rather critically, recursives need to reach into their child assembler and invalidate them.

For all the paths around scalar children, invalidating the child
assembler's pointer back to parent has been sufficient to obstruct any
problematic mutations, but with how directly the operations on map
children are passed through to their 'w' target, we also need to do
an invalidation that affects there.

_rsrch/nodesolution/impls/map.go

@@ -376,5 +376,7 @@ func (ma *plainMap__ValueAssemblerMap) Finish() error {
 	if err := ma.ca.Finish(); err != nil {
 		return err
 	}
-	return ma.p.va.AssignNode(ma.ca.w)
+	w := ma.ca.w
+	ma.ca.w = nil
+	return ma.p.va.AssignNode(w)
 }