perf(notifications): memoize getNotificationType per push-rules object and room

Fixes #77

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/app/utils/room.ts

@@ -188,7 +188,11 @@ export const isMutedRule = (rule: IPushRule) =>
 export const findMutedRule = (overrideRules: IPushRule[], roomId: string) =>
   overrideRules.find((rule) => rule.rule_id === roomId && isMutedRule(rule));
 
-export const getNotificationType = (mx: MatrixClient, roomId: string): NotificationType => {
+const computeNotificationType = (
+  mx: MatrixClient,
+  roomId: string,
+  pushRulesContent: IPushRules | undefined,
+): NotificationType => {
   let roomPushRule: IPushRule | undefined;
   try {
     roomPushRule = mx.getRoomPushRule('global', roomId);
@@ -197,8 +201,7 @@ export const getNotificationType = (mx: MatrixClient, roomId: string): Notificat
   }
 
   if (!roomPushRule) {
-    const overrideRules = mx.getAccountData(EventType.PushRules)?.getContent<IPushRules>()
-      ?.global?.override;
+    const overrideRules = pushRulesContent?.global?.override;
     if (!overrideRules) return NotificationType.Default;
 
     return findMutedRule(overrideRules, roomId) ? NotificationType.Mute : NotificationType.Default;
@@ -208,6 +211,37 @@ export const getNotificationType = (mx: MatrixClient, roomId: string): Notificat
   return NotificationType.MentionsAndKeywords;
 };
 
+// #77 — `getNotificationType` is called synchronously for every live timeline
+// event in every room, but its result only ever changes when the `m.push_rules`
+// account-data event updates. matrix-js-sdk replaces the stored account-data
+// `MatrixEvent`'s content wholesale on every `m.push_rules` update (see
+// `store.storeAccountDataEvents`), so keying a cache off that content object's
+// identity naturally invalidates itself on `ClientEvent.AccountData` without
+// needing an explicit listener here. A bursty sync backlog across many rooms
+// then hits this cache instead of re-running `getRoomPushRule` + a linear scan
+// of the override rules per event.
+const notificationTypeCache = new WeakMap<object, Map<string, NotificationType>>();
+// Stable key to use when there is no push-rules account data at all yet.
+const NO_PUSH_RULES_KEY: object = {};
+
+export const getNotificationType = (mx: MatrixClient, roomId: string): NotificationType => {
+  const pushRulesContent = mx.getAccountData(EventType.PushRules)?.getContent<IPushRules>();
+  const cacheKey = pushRulesContent ?? NO_PUSH_RULES_KEY;
+
+  let roomCache = notificationTypeCache.get(cacheKey);
+  if (!roomCache) {
+    roomCache = new Map();
+    notificationTypeCache.set(cacheKey, roomCache);
+  }
+
+  const cached = roomCache.get(roomId);
+  if (cached !== undefined) return cached;
+
+  const result = computeNotificationType(mx, roomId, pushRulesContent);
+  roomCache.set(roomId, result);
+  return result;
+};
+
 const NOTIFICATION_EVENT_TYPES = [
   'm.room.create',
   'm.room.message',