perf(frontend): reduce api requests for non-logged-in enviroment (#15001)

* wip

* Update CHANGELOG.md

* wip

packages/frontend/src/server-context.ts

@@ -0,0 +1,23 @@
+/*
+ * SPDX-FileCopyrightText: syuilo and misskey-project
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+import * as Misskey from 'misskey-js';
+import { $i } from '@/account.js';
+
+const providedContextEl = document.getElementById('misskey_clientCtx');
+
+export type ServerContext = {
+	clip?: Misskey.entities.Clip;
+	note?: Misskey.entities.Note;
+	user?: Misskey.entities.UserLite;
+} | null;
+
+export const serverContext: ServerContext = (providedContextEl && providedContextEl.textContent) ? JSON.parse(providedContextEl.textContent) : null;
+
+export function getServerContext<K extends keyof NonNullable<ServerContext>>(entity: K): Required<Pick<NonNullable<ServerContext>, K>> | null {
+	// contextは非ログイン状態の情報しかないためログイン時は利用できない
+	if ($i) return null;
+
+	return serverContext ? (serverContext[entity] ?? null) : null;
+}