fix(slack): bound username cache with ttl and lru eviction

src/channels/slack/adapter.test.ts

@@ -1,4 +1,4 @@
-import { describe, it, expect, vi, beforeEach } from 'vitest';
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
 
 // ── Mock @slack/bolt before importing adapter ──────────────────────
 
@@ -66,6 +66,10 @@ describe('SlackAdapter', () => {
     adapter = new SlackAdapter(baseConfig);
   });
 
+  afterEach(() => {
+    vi.useRealTimers();
+  });
+
   // ── Basic properties ──────────────────────────────────────────
 
   it('has name "slack"', () => {
@@ -221,6 +225,52 @@ describe('SlackAdapter', () => {
     expect(msg.senderId).toBe('C123:2222.3333');
   });
 
+  it('caches resolved usernames and avoids repeated users.info calls', async () => {
+    const handler = vi.fn();
+    adapter.onMessage(handler);
+    await adapter.connect();
+
+    await simulateMessage({
+      ts: '1111.0001',
+      channel: 'C123',
+      user: 'U456',
+      text: 'First message',
+    });
+    await simulateMessage({
+      ts: '1111.0002',
+      channel: 'C123',
+      user: 'U456',
+      text: 'Second message',
+    });
+
+    expect(mockUsersInfo).toHaveBeenCalledTimes(1);
+  });
+
+  it('refreshes cached usernames after TTL expiry', async () => {
+    vi.useFakeTimers();
+    const handler = vi.fn();
+    adapter.onMessage(handler);
+    await adapter.connect();
+
+    await simulateMessage({
+      ts: '2222.0001',
+      channel: 'C123',
+      user: 'U456',
+      text: 'First message',
+    });
+    expect(mockUsersInfo).toHaveBeenCalledTimes(1);
+
+    vi.advanceTimersByTime(60 * 60 * 1_000 + 1);
+
+    await simulateMessage({
+      ts: '2222.0002',
+      channel: 'C123',
+      user: 'U456',
+      text: 'Second message after TTL',
+    });
+    expect(mockUsersInfo).toHaveBeenCalledTimes(2);
+  });
+
   it('ignores bot messages (bot_id present)', async () => {
     const handler = vi.fn();
     adapter.onMessage(handler);

src/channels/slack/adapter.ts

@@ -31,6 +31,11 @@ export interface SlackAdapterConfig {
   pairingManager?: PairingManager;
 }
 
+interface CachedUserName {
+  name: string;
+  expiresAt: number;
+}
+
 /** Minimal shape of a Slack message event from Bolt. */
 interface SlackMessageEvent {
   ts?: string;
@@ -63,8 +68,10 @@ export class SlackAdapter implements ChannelAdapter {
   private app: App | null = null;
   private messageHandler?: (msg: InboundMessage) => void;
   private config: SlackAdapterConfig;
-  private userNameCache: Map<string, string> = new Map();
+  private userNameCache: Map<string, CachedUserName> = new Map();
   private botUserId?: string;
+  private readonly userNameCacheTtlMs = 60 * 60 * 1_000;
+  private readonly userNameCacheMaxEntries = 1_000;
 
   get status(): ChannelStatus {
     return this._status;
@@ -199,13 +206,28 @@ export class SlackAdapter implements ChannelAdapter {
 
   /** Resolve a Slack user ID to a display name, with caching. */
   private async resolveUserName(userId: string): Promise<string> {
+    const now = Date.now();
     const cached = this.userNameCache.get(userId);
-    if (cached) {return cached;}
+    if (cached && cached.expiresAt > now) {
+      // Refresh LRU order on cache hit.
+      this.userNameCache.delete(userId);
+      this.userNameCache.set(userId, cached);
+      return cached.name;
+    }
+    if (cached) {
+      this.userNameCache.delete(userId);
+    }
 
     try {
       const result = await this.app!.client.users.info({ user: userId });
       const name = result.user?.real_name || result.user?.name || userId;
-      this.userNameCache.set(userId, name);
+      this.userNameCache.set(userId, { name, expiresAt: now + this.userNameCacheTtlMs });
+      if (this.userNameCache.size > this.userNameCacheMaxEntries) {
+        const oldestKey = this.userNameCache.keys().next().value;
+        if (typeof oldestKey === 'string') {
+          this.userNameCache.delete(oldestKey);
+        }
+      }
       return name;
     } catch {
       return userId;