perf: coalesce slack user info lookups

turbo/apps/api/src/lib/slack-webhook-context.ts

@@ -4,6 +4,7 @@ import {
   fetchSlackUserInfoMap,
   formatSenderBlock,
   type SlackUserInfo,
+  type SlackUserInfoResolver,
 } from "../signals/external/slack-message-client";
 
 export interface SlackFile {
@@ -101,6 +102,11 @@ export interface SlackConversationContextObserver {
   ) => void;
 }
 
+interface SlackConversationContextOptions {
+  readonly observer?: SlackConversationContextObserver;
+  readonly userInfoResolver?: SlackUserInfoResolver;
+}
+
 async function fetchThreadContext(
   client: WebClient,
   channel: string,
@@ -473,8 +479,9 @@ export async function fetchConversationContexts(
   channelId: string,
   threadTs: string | undefined,
   currentMessageTs?: string,
-  observer?: SlackConversationContextObserver,
+  options?: SlackConversationContextOptions,
 ): Promise<{ readonly executionContext: string }> {
+  const observer = options?.observer;
   const measureContext = async <T>(
     phase: SlackConversationContextPhase,
     operation: () => T | Promise<T>,
@@ -541,7 +548,11 @@ export async function fetchConversationContexts(
     ),
   });
   const userInfoMap = await measureContext("user_info", async () => {
-    return await fetchSlackUserInfoMap(client, userInfoIds);
+    return await fetchSlackUserInfoMap(
+      client,
+      userInfoIds,
+      options?.userInfoResolver,
+    );
   });
   const { channelContextPrefix, threadExecContext } = await measureContext(
     "format",
@@ -570,6 +581,7 @@ export async function enrichMessageContent(opts: {
   readonly files: readonly SlackFile[] | undefined;
   readonly client: WebClient;
   readonly userId: string;
+  readonly userInfoResolver?: SlackUserInfoResolver;
 }): Promise<{
   readonly prompt: string;
   readonly userInfoExtras: {
@@ -583,10 +595,11 @@ export async function enrichMessageContent(opts: {
   }
 
   const mentionedIds = extractMentionedUserIds([{ text: opts.messageContent }]);
-  const userInfoMap = await fetchSlackUserInfoMap(opts.client, [
-    opts.userId,
-    ...mentionedIds,
-  ]);
+  const userInfoMap = await fetchSlackUserInfoMap(
+    opts.client,
+    [opts.userId, ...mentionedIds],
+    opts.userInfoResolver,
+  );
   prompt = resolveUserMentions(prompt, userInfoMap);
 
   const currentUser = userInfoMap.get(opts.userId);

turbo/apps/api/src/signals/external/slack-message-client.ts

@@ -6,7 +6,7 @@ import {
 } from "@slack/web-api";
 
 import { optionalEnv } from "../../lib/env";
-import { settle } from "../utils";
+import { onRejection, settle } from "../utils";
 
 type OpenDmResult =
   | { readonly kind: "ok"; readonly channelId: string }
@@ -191,6 +191,20 @@ export interface SlackUserInfo {
   readonly timezone?: string;
 }
 
+export interface SlackUserInfoResolverStats {
+  readonly requestedCount: number;
+  readonly cacheHitCount: number;
+  readonly missCount: number;
+  readonly inFlightHitCount: number;
+}
+
+export interface SlackUserInfoResolver {
+  readonly resolveMany: (
+    userIds: readonly string[],
+  ) => Promise<Map<string, SlackUserInfo>>;
+  readonly stats: () => SlackUserInfoResolverStats;
+}
+
 export function formatSenderBlock(info: SlackUserInfo): string {
   const parts = [`id: ${info.id}`];
   if (info.name) {
@@ -231,10 +245,93 @@ async function fetchSlackUserInfo(
   };
 }
 
+export function createSlackUserInfoResolver(
+  client: WebClient,
+): SlackUserInfoResolver {
+  const cache = new Map<string, SlackUserInfo>();
+  const inFlight = new Map<string, Promise<SlackUserInfo | undefined>>();
+  let requestedCount = 0;
+  let cacheHitCount = 0;
+  let missCount = 0;
+  let inFlightHitCount = 0;
+
+  const startLookup = (userId: string): Promise<SlackUserInfo | undefined> => {
+    const promise = onRejection(
+      (async () => {
+        const info = await fetchSlackUserInfo(client, userId);
+        if (info) {
+          cache.set(userId, info);
+        }
+        inFlight.delete(userId);
+        return info;
+      })(),
+      () => {
+        inFlight.delete(userId);
+      },
+    );
+    inFlight.set(userId, promise);
+    return promise;
+  };
+
+  const resolveOne = async (
+    userId: string,
+  ): Promise<SlackUserInfo | undefined> => {
+    const cached = cache.get(userId);
+    if (cached) {
+      cacheHitCount += 1;
+      return cached;
+    }
+
+    const active = inFlight.get(userId);
+    if (active) {
+      inFlightHitCount += 1;
+      return await active;
+    }
+
+    missCount += 1;
+    return await startLookup(userId);
+  };
+
+  return {
+    async resolveMany(userIds) {
+      const map = new Map<string, SlackUserInfo>();
+      const uniqueIds = [...new Set(userIds)];
+      requestedCount += uniqueIds.length;
+      const results = await Promise.allSettled(
+        uniqueIds.map(async (id) => {
+          const info = await resolveOne(id);
+          return { id, info };
+        }),
+      );
+
+      for (const result of results) {
+        if (result.status === "fulfilled" && result.value.info) {
+          map.set(result.value.id, result.value.info);
+        }
+      }
+
+      return map;
+    },
+    stats() {
+      return {
+        requestedCount,
+        cacheHitCount,
+        missCount,
+        inFlightHitCount,
+      };
+    },
+  };
+}
+
 export async function fetchSlackUserInfoMap(
   client: WebClient,
   userIds: readonly string[],
+  resolver?: SlackUserInfoResolver,
 ): Promise<Map<string, SlackUserInfo>> {
+  if (resolver) {
+    return await resolver.resolveMany(userIds);
+  }
+
   const map = new Map<string, SlackUserInfo>();
   const uniqueIds = [...new Set(userIds)];
   const results = await Promise.allSettled(

turbo/apps/api/src/signals/routes/__tests__/integrations.bdd.test.ts

@@ -1193,6 +1193,7 @@ describe("INT-01: Slack app deep webhook flows", () => {
       "api_dispatch_pre_create_zero_slack_build_run_params_fetch_conversation_context_history",
       "api_dispatch_pre_create_zero_slack_build_run_params_fetch_conversation_context_user_info",
       "api_dispatch_pre_create_zero_slack_build_run_params_fetch_conversation_context_format",
+      "api_dispatch_pre_create_zero_slack_build_run_params_user_info_resolver",
       "api_dispatch_pre_create_zero_slack_build_run_params_assemble",
       "api_dispatch_pre_create_zero_slack_create_run",
     ]) {