Support captured CRDT changes in compound transaction contracts

src/capability-model/validation.ts

@@ -1,3 +1,4 @@
+import { isStorableType } from "./generics.js";
 import { validateInitialization } from "./initialization.js";
 import { validateExecutionContracts } from "./execution.js";
 import { resolveForwardedBinding, type ConcreteBinding } from "./forwarding.js";
@@ -244,6 +245,15 @@ const validateValueType = (
       requireText(issues, type.descriptorId, `${path}.descriptorId`, "Message descriptor identity");
       return;
     case "change":
+      if (!isStorableType(type.value))
+        issue(
+          issues,
+          "invalid-value-type",
+          path,
+          "change<T> requires a storable materialized type, not references or nested changes",
+        );
+      validateValueType(issues, type.value, path + ".value", indexes);
+      return;
     case "optional":
     case "list":
       validateValueType(issues, type.value, `${path}.value`, indexes);