feat: (prospectively) use watchPromise() to wait for contract finish

packages/zoe/src/zoeService/startInstance.js

@@ -1,3 +1,5 @@
+/* global globalThis */
+
 /* eslint @typescript-eslint/no-floating-promises: "warn" */
 import { E } from '@endo/eventual-send';
 import { passStyleOf } from '@endo/marshal';
@@ -6,6 +8,7 @@ import {
   makeScalarBigMapStore,
   provideDurableWeakMapStore,
   prepareExoClass,
+  prepareExo,
 } from '@agoric/vat-data';
 import { initEmpty } from '@agoric/store';
 
@@ -131,10 +134,10 @@ export const makeStartInstance = (
       replaceAllocations(seatHandleAllocations) {
         const { state } = this;
         try {
-          seatHandleAllocations.forEach(({ seatHandle, allocation }) => {
+          for (const { seatHandle, allocation } of seatHandleAllocations) {
             const zoeSeatAdmin = state.seatHandleToSeatAdmin.get(seatHandle);
             zoeSeatAdmin.replaceAllocation(allocation);
-          });
+          }
         } catch (err) {
           // nothing for Zoe to do if the termination fails
           void E(state.adminNode).terminateWithFailure(err);
@@ -225,6 +228,20 @@ export const makeStartInstance = (
     },
   );
 
+  const watcher = prepareExo(
+    zoeBaggage,
+    'InstanceCompletionWatcher',
+    M.interface('InstanceCompletionWatcher', {
+      onFulfilled: M.call(M.any()).returns(),
+      onRejected: M.call(M.any()).returns(),
+    }),
+    {
+      onFulfilled: (completion, instanceAdmin) =>
+        instanceAdmin.exitAllSeats(completion),
+      onRejected: (reason, instanceAdmin) => instanceAdmin.failAllSeats(reason),
+    },
+  );
+
   const startInstance = async (
     installationP,
     uncleanIssuerKeywordRecord = harden({}),
@@ -278,12 +295,10 @@ export const makeStartInstance = (
     );
     zoeInstanceStorageManager.initInstanceAdmin(instanceHandle, instanceAdmin);
 
-    E.when(
+    globalThis.VatData.watchPromise(
       E(adminNode).done(),
-      completion => {
-        instanceAdmin.exitAllSeats(completion);
-      },
-      reason => instanceAdmin.failAllSeats(reason),
+      watcher,
+      instanceAdmin,
     );
 
     /** @type {ZoeInstanceAdmin} */