Add preliminary message backup harness

ts/ConversationController.ts

@@ -4,6 +4,7 @@
 import { debounce, pick, uniq, without } from 'lodash';
 import PQueue from 'p-queue';
 import { v4 as generateUuid } from 'uuid';
+import { batch as batchDispatch } from 'react-redux';
 
 import type {
   ConversationModelCollectionType,
@@ -831,7 +832,7 @@ export class ConversationController {
   // Note: `doCombineConversations` is directly used within this function since both
   //   run on `_combineConversationsQueue` queue and we don't want deadlocks.
   private async doCheckForConflicts(): Promise<void> {
-    log.info('checkForConflicts: starting...');
+    log.info('ConversationController.checkForConflicts: starting...');
     const byServiceId = Object.create(null);
     const byE164 = Object.create(null);
     const byGroupV2Id = Object.create(null);
@@ -1420,13 +1421,17 @@ export class ConversationController {
       );
       await queue.onIdle();
 
-      // Hydrate the final set of conversations
-      this._conversations.add(
-        collection.filter(conversation => !conversation.isTemporary)
-      );
-
+      // It is alright to call it first because the 'add'/'update' events are
+      // triggered after updating the collection.
       this._initialFetchComplete = true;
 
+      // Hydrate the final set of conversations
+      batchDispatch(() => {
+        this._conversations.add(
+          collection.filter(conversation => !conversation.isTemporary)
+        );
+      });
+
       await Promise.all(
         this._conversations.map(async conversation => {
           try {
@@ -1466,7 +1471,10 @@ export class ConversationController {
           }
         })
       );
-      log.info('ConversationController: done with initial fetch');
+      log.info(
+        'ConversationController: done with initial fetch, ' +
+          `got ${this._conversations.length} conversations`
+      );
     } catch (error) {
       log.error(
         'ConversationController: initial fetch failed',