wip(0.S3): ui blocks, scene on enter/exit, hooks, machines over a state's field, namespace and engine-system injection; a reference out of a read-only state or a module let is read-only; deps counts writes into another module's state; the rejected examples hold states

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

examples/rejected/uses_pkg_mech/index.ludic

@@ -4,5 +4,5 @@ module mech uses ludic_base
 import "ludic.base"
 import "ludic.inventory"
 export function stock() -> int {
-  return inv_count(0)
+  return inv_limit(0)
 }