Improve username validity checks

Co-authored-by: trevor-signal <131492920+trevor-signal@users.noreply.github.com>

ts/models/conversations.preload.ts

@@ -267,6 +267,7 @@ import { maybeNotify } from '../messages/maybeNotify.preload.js';
 import { missingCaseError } from '../util/missingCaseError.std.js';
 import * as Message from '../types/Message2.preload.js';
 import { itemStorage } from '../textsecure/Storage.preload.js';
+import { isUsernameValid } from '../util/Username.dom.js';
 
 const { compact, isNumber, throttle, debounce } = lodash;
 
@@ -4454,6 +4455,16 @@ export class ConversationModel {
       return;
     }
 
+    if (username && !isUsernameValid(username)) {
+      log.error(
+        `updateUsername(${this.idForLogging()}): username is invalid, dropping`,
+        {
+          fromStorageService,
+        }
+      );
+      return;
+    }
+
     log.info(`updateUsername(${this.idForLogging()}): updating username`);
 
     this.#doSet({ username });

ts/services/backups/export.preload.ts

@@ -1259,7 +1259,7 @@ export class BackupExportStream extends Readable {
             aci,
             pni,
             e164,
-            username: convo.username ?? null,
+            username: convo.username || null,
             blocked: convo.serviceId
               ? itemStorage.blocked.isServiceIdBlocked(convo.serviceId)
               : null,

ts/services/storageRecordOps.preload.ts

@@ -1378,7 +1378,7 @@ export async function mergeContactRecord(
     };
   }
 
-  await conversation.updateUsername(dropNull(contactRecord.username), {
+  await conversation.updateUsername(dropNull(contactRecord.username || null), {
     shouldSave: false,
     fromStorageService: true,
   });
@@ -1986,7 +1986,7 @@ export async function mergeAccountRecord(
     needsStorageServiceSync: false,
   });
 
-  await conversation.updateUsername(dropNull(username), {
+  await conversation.updateUsername(dropNull(username || null), {
     shouldSave: false,
     fromStorageService: true,
   });