enhance(backend): refine system account (#15530)

* wip

* wip

* wip

* Update SystemAccountService.ts

* Update 1740121393164-system-accounts.js

* Update DeleteAccountService.ts

* wip

* wip

* wip

* wip

* Update 1740121393164-system-accounts.js

* Update RepositoryModule.ts

* wip

* wip

* wip

* Update ApRendererService.ts

* wip

* wip

* Update SystemAccountService.ts

* fix tests

* fix tests

* fix tests

* fix tests

* fix tests

* fix tests

* add print logs

* ログが長すぎて出てないかもしれない

* fix migration

* refactor

* fix fed-tests

* Update RelayService.ts

* merge

* Update user.test.ts

* chore: emit log

* fix: tweak sleep duration

* fix: exit 1

* fix: wait for misskey processes to become healthy

* fix: longer sleep for user deletion

* fix: make sleep longer again

* デッドロック解消の試み

https://github.com/misskey-dev/misskey/issues/15005

* Revert "デッドロック解消の試み"

This reverts commit 266141f66f.

* wip

* Update SystemAccountService.ts

---------

Co-authored-by: おさむのひと <46447427+samunohito@users.noreply.github.com>
Co-authored-by: zyoshoka <107108195+zyoshoka@users.noreply.github.com>

packages/backend/src/server/api/endpoints/admin/meta.ts

@@ -9,6 +9,7 @@ import { MetaService } from '@/core/MetaService.js';
 import type { Config } from '@/config.js';
 import { DI } from '@/di-symbols.js';
 import { DEFAULT_POLICIES } from '@/core/RoleService.js';
+import { SystemAccountService } from '@/core/SystemAccountService.js';
 
 export const meta = {
 	tags: ['meta'],
@@ -237,7 +238,7 @@ export const meta = {
 			},
 			proxyAccountId: {
 				type: 'string',
-				optional: false, nullable: true,
+				optional: false, nullable: false,
 				format: 'id',
 			},
 			email: {
@@ -545,10 +546,13 @@ export default class extends Endpoint<typeof meta, typeof paramDef> { // eslint-
 		private config: Config,
 
 		private metaService: MetaService,
+		private systemAccountService: SystemAccountService,
 	) {
 		super(meta, paramDef, async () => {
 			const instance = await this.metaService.fetch(true);
 
+			const proxy = await this.systemAccountService.fetch('proxy');
+
 			return {
 				maintainerName: instance.maintainerName,
 				maintainerEmail: instance.maintainerEmail,
@@ -613,7 +617,7 @@ export default class extends Endpoint<typeof meta, typeof paramDef> { // eslint-
 				sensitiveMediaDetectionSensitivity: instance.sensitiveMediaDetectionSensitivity,
 				setSensitiveFlagAutomatically: instance.setSensitiveFlagAutomatically,
 				enableSensitiveMediaDetectionForVideos: instance.enableSensitiveMediaDetectionForVideos,
-				proxyAccountId: instance.proxyAccountId,
+				proxyAccountId: proxy.id,
 				email: instance.email,
 				smtpSecure: instance.smtpSecure,
 				smtpHost: instance.smtpHost,