From 8ce7cc8aae5b11d45993e82d2e0db0c7fbe52fa2 Mon Sep 17 00:00:00 2001
From: Vincent Koc <vincentkoc@ieee.org>
Date: Sun, 3 May 2026 10:35:10 -0700
Subject: [PATCH] perf(slack): cache stream recipient team lookup

---
 .../dispatch.streaming.test.ts                | 27 +++++++++-
 .../src/monitor/message-handler/dispatch.ts   | 50 +++++++++++++++++++
 2 files changed, 76 insertions(+), 1 deletion(-)

diff --git a/extensions/slack/src/monitor/message-handler/dispatch.streaming.test.ts b/extensions/slack/src/monitor/message-handler/dispatch.streaming.test.ts
index 86666f5d3cc..5c3897d6f13 100644
--- a/extensions/slack/src/monitor/message-handler/dispatch.streaming.test.ts
+++ b/extensions/slack/src/monitor/message-handler/dispatch.streaming.test.ts
@@ -1,7 +1,8 @@
-import { describe, expect, it, vi } from "vitest";
+import { afterEach, describe, expect, it, vi } from "vitest";
 import {
   createSlackTurnDeliveryTracker,
   isSlackStreamingEnabled,
+  resetSlackStreamRecipientTeamCacheForTests,
   resolveSlackDisableBlockStreaming,
   resolveSlackStreamRecipientTeamId,
   resolveSlackStreamingThreadHint,
@@ -9,6 +10,10 @@ import {
   shouldInitializeSlackDraftStream,
 } from "./dispatch.js";
 
+afterEach(() => {
+  resetSlackStreamRecipientTeamCacheForTests();
+});
+
 describe("slack native streaming defaults", () => {
   it("is enabled for partial mode when native streaming is on", () => {
     expect(isSlackStreamingEnabled({ mode: "partial", nativeStreaming: true })).toBe(true);
@@ -93,6 +98,26 @@ describe("slack native streaming recipient team", () => {
       }),
     ).toBe("T_LOCAL");
   });
+
+  it("caches resolved user teams for repeated stream starts", async () => {
+    const usersInfo = vi.fn(async () => ({
+      user: { team_id: "T_LOOKUP" },
+    }));
+    const params = {
+      client: {
+        users: {
+          info: usersInfo,
+        },
+      } as never,
+      token: "xoxb-test",
+      userId: "U_REMOTE",
+      fallbackTeamId: "T_LOCAL",
+    };
+
+    await expect(resolveSlackStreamRecipientTeamId(params)).resolves.toBe("T_LOOKUP");
+    await expect(resolveSlackStreamRecipientTeamId(params)).resolves.toBe("T_LOOKUP");
+    expect(usersInfo).toHaveBeenCalledTimes(1);
+  });
 });
 
 describe("slack turn delivery tracker", () => {
diff --git a/extensions/slack/src/monitor/message-handler/dispatch.ts b/extensions/slack/src/monitor/message-handler/dispatch.ts
index 1e1db60f8e2..dc82dfa6595 100644
--- a/extensions/slack/src/monitor/message-handler/dispatch.ts
+++ b/extensions/slack/src/monitor/message-handler/dispatch.ts
@@ -171,6 +171,9 @@ type SlackTurnDeliveryAttempt = {
   textOverride?: string;
 };
 
+const SLACK_STREAM_RECIPIENT_TEAM_CACHE_MAX = 2000;
+const slackStreamRecipientTeamCache = new Map<string, string>();
+
 function buildSlackTurnDeliveryKey(params: SlackTurnDeliveryAttempt): string | null {
   const reply = resolveSendableOutboundReplyParts(params.payload, {
     text: params.textOverride,
@@ -189,6 +192,48 @@ function buildSlackTurnDeliveryKey(params: SlackTurnDeliveryAttempt): string | n
   });
 }
 
+function readSlackStreamRecipientTeamCache(params: {
+  fallbackTeamId?: string;
+  userId?: string;
+}): string | undefined {
+  if (!params.fallbackTeamId || !params.userId) {
+    return undefined;
+  }
+  const cacheKey = `${params.fallbackTeamId}:${params.userId}`;
+  const cached = slackStreamRecipientTeamCache.get(cacheKey);
+  if (!cached) {
+    return undefined;
+  }
+  slackStreamRecipientTeamCache.delete(cacheKey);
+  slackStreamRecipientTeamCache.set(cacheKey, cached);
+  return cached;
+}
+
+function rememberSlackStreamRecipientTeam(params: {
+  fallbackTeamId?: string;
+  userId?: string;
+  teamId: string;
+}): void {
+  if (!params.fallbackTeamId || !params.userId) {
+    return;
+  }
+  const cacheKey = `${params.fallbackTeamId}:${params.userId}`;
+  if (slackStreamRecipientTeamCache.has(cacheKey)) {
+    slackStreamRecipientTeamCache.delete(cacheKey);
+  }
+  slackStreamRecipientTeamCache.set(cacheKey, params.teamId);
+  if (slackStreamRecipientTeamCache.size > SLACK_STREAM_RECIPIENT_TEAM_CACHE_MAX) {
+    const oldest = slackStreamRecipientTeamCache.keys().next().value;
+    if (oldest) {
+      slackStreamRecipientTeamCache.delete(oldest);
+    }
+  }
+}
+
+export function resetSlackStreamRecipientTeamCacheForTests(): void {
+  slackStreamRecipientTeamCache.clear();
+}
+
 export function createSlackTurnDeliveryTracker() {
   const deliveredKeys = new Set<string>();
   return {
@@ -225,6 +270,10 @@ export async function resolveSlackStreamRecipientTeamId(params: {
   userId?: PreparedSlackMessage["message"]["user"];
   fallbackTeamId?: string;
 }): Promise<string | undefined> {
+  const cachedTeamId = readSlackStreamRecipientTeamCache(params);
+  if (cachedTeamId) {
+    return cachedTeamId;
+  }
   if (params.userId) {
     try {
       const info = await params.client.users.info({
@@ -233,6 +282,7 @@ export async function resolveSlackStreamRecipientTeamId(params: {
       });
       const teamId = info.user?.team_id ?? info.user?.profile?.team;
       if (teamId) {
+        rememberSlackStreamRecipientTeam({ ...params, teamId });
         return teamId;
       }
     } catch (err) {