feat: preserved usernames

Resolve #10704

packages/backend/src/server/api/endpoints/username/available.ts

@@ -4,6 +4,7 @@ import type { UsedUsernamesRepository, UsersRepository } from '@/models/index.js
 import { Endpoint } from '@/server/api/endpoint-base.js';
 import { localUsernameSchema } from '@/models/entities/User.js';
 import { DI } from '@/di-symbols.js';
+import { MetaService } from '@/core/MetaService.js';
 
 export const meta = {
 	tags: ['users'],
@@ -39,9 +40,10 @@ export default class extends Endpoint<typeof meta, typeof paramDef> {
 
 		@Inject(DI.usedUsernamesRepository)
 		private usedUsernamesRepository: UsedUsernamesRepository,
+
+		private metaService: MetaService,
 	) {
 		super(meta, paramDef, async (ps, me) => {
-			// Get exist
 			const exist = await this.usersRepository.countBy({
 				host: IsNull(),
 				usernameLower: ps.username.toLowerCase(),
@@ -49,8 +51,11 @@ export default class extends Endpoint<typeof meta, typeof paramDef> {
 
 			const exist2 = await this.usedUsernamesRepository.countBy({ username: ps.username.toLowerCase() });
 
+			const meta = await this.metaService.fetch();
+			const isPreserved = meta.preservedUsernames.map(x => x.toLowerCase()).includes(ps.username.toLowerCase());
+
 			return {
-				available: exist === 0 && exist2 === 0,
+				available: exist === 0 && exist2 === 0 && !isPreserved,
 			};
 		});
 	}