perf(main): refresh message feed cache in background

src/main/services/team/TeamMessageFeedService.ts

@@ -449,6 +449,14 @@ export class TeamMessageFeedService {
         messages: cached.messages,
       };
     }
+    if (cached && !cacheDirty && cacheExpired) {
+      this.refreshCleanExpiredCacheInBackground(teamName, cached, now);
+      return {
+        teamName,
+        feedRevision: cached.feedRevision,
+        messages: cached.messages,
+      };
+    }
 
     const existingRequest = this.inFlightByTeam.get(teamName);
     const generationAtStart = this.getGeneration(teamName);
@@ -479,6 +487,43 @@ export class TeamMessageFeedService {
     return this.generationByTeam.get(teamName) ?? 0;
   }
 
+  private refreshCleanExpiredCacheInBackground(
+    teamName: string,
+    cached: TeamMessageFeedCacheEntry,
+    now: number
+  ): void {
+    const generationAtStart = this.getGeneration(teamName);
+    const existingRequest = this.inFlightByTeam.get(teamName);
+    if (existingRequest?.generationAtStart === generationAtStart) {
+      return;
+    }
+
+    const request = this.buildFeed(teamName, cached, now, false, true, generationAtStart).catch(
+      (error) => {
+        logger.debug(
+          `[${teamName}] background message feed refresh failed: ${
+            error instanceof Error ? error.message : String(error)
+          }`
+        );
+        return {
+          teamName,
+          feedRevision: cached.feedRevision,
+          messages: cached.messages,
+        };
+      }
+    );
+
+    const trackedRequest = request.finally(() => {
+      if (this.inFlightByTeam.get(teamName)?.promise === trackedRequest) {
+        this.inFlightByTeam.delete(teamName);
+      }
+    });
+    this.inFlightByTeam.set(teamName, {
+      promise: trackedRequest,
+      generationAtStart,
+    });
+  }
+
   private async buildFeed(
     teamName: string,
     cached: TeamMessageFeedCacheEntry | undefined,

test/main/services/team/TeamMessageFeedService.test.ts

@@ -167,9 +167,12 @@ Messages:
     ]);
   });
 
-  it('refreshes the durable feed after cache expiry even when the dirty signal was missed', async () => {
-    let inboxMessages: InboxMessage[] = [makeMessage()];
-    const getInboxMessages = vi.fn(async () => inboxMessages);
+  it('returns clean expired cache immediately and refreshes durable feed in the background', async () => {
+    const refreshRequest = createDeferred<InboxMessage[]>();
+    const getInboxMessages = vi
+      .fn()
+      .mockResolvedValueOnce([makeMessage()])
+      .mockImplementationOnce(() => refreshRequest.promise);
     const service = new TeamMessageFeedService({
       getConfig: vi.fn(async () => config),
       getInboxMessages,
@@ -179,7 +182,7 @@ Messages:
 
     await service.getFeed('signal-ops-4');
 
-    inboxMessages = [
+    const refreshedMessages = [
       makeMessage({
         from: 'jack',
         to: 'user',
@@ -192,6 +195,15 @@ Messages:
 
     vi.setSystemTime(new Date('2026-04-19T18:46:46.500Z'));
 
+    const stale = await service.getFeed('signal-ops-4');
+    expect(getInboxMessages).toHaveBeenCalledTimes(2);
+    expect(stale.messages).toHaveLength(1);
+
+    refreshRequest.resolve(refreshedMessages);
+    await refreshRequest.promise;
+    await Promise.resolve();
+    await Promise.resolve();
+
     const refreshed = await service.getFeed('signal-ops-4');
     expect(getInboxMessages).toHaveBeenCalledTimes(2);
     expect(