fix: resolve heartbeat sender and Slack thread_ts

src/slack/monitor/message-handler.ts

@@ -8,6 +8,7 @@ import type { SlackMessageEvent } from "../types.js";
 import type { SlackMonitorContext } from "./context.js";
 import { dispatchPreparedSlackMessage } from "./message-handler/dispatch.js";
 import { prepareSlackMessage } from "./message-handler/prepare.js";
+import { createSlackThreadTsResolver } from "./thread-resolution.js";
 
 export type SlackMessageHandler = (
   message: SlackMessageEvent,
@@ -20,6 +21,7 @@ export function createSlackMessageHandler(params: {
 }): SlackMessageHandler {
   const { ctx, account } = params;
   const debounceMs = resolveInboundDebounceMs({ cfg: ctx.cfg, channel: "slack" });
+  const threadTsResolver = createSlackThreadTsResolver({ client: ctx.app.client });
 
   const debouncer = createInboundDebouncer<{
     message: SlackMessageEvent;
@@ -29,9 +31,13 @@ export function createSlackMessageHandler(params: {
     buildKey: (entry) => {
       const senderId = entry.message.user ?? entry.message.bot_id;
       if (!senderId) return null;
+      const messageTs = entry.message.ts ?? entry.message.event_ts;
+      // If Slack flags a thread reply but omits thread_ts, isolate it from root debouncing.
       const threadKey = entry.message.thread_ts
         ? `${entry.message.channel}:${entry.message.thread_ts}`
-        : entry.message.channel;
+        : entry.message.parent_user_id && messageTs
+          ? `${entry.message.channel}:maybe-thread:${messageTs}`
+          : entry.message.channel;
       return `slack:${ctx.accountId}:${threadKey}:${senderId}`;
     },
     shouldDebounce: (entry) => {
@@ -91,6 +97,7 @@ export function createSlackMessageHandler(params: {
       return;
     }
     if (ctx.markMessageSeen(message.channel, message.ts)) return;
-    await debouncer.enqueue({ message, opts });
+    const resolvedMessage = await threadTsResolver.resolve({ message, source: opts.source });
+    await debouncer.enqueue({ message: resolvedMessage, opts });
   };
 }

src/slack/monitor/thread-resolution.test.ts

@@ -0,0 +1,30 @@
+import { describe, expect, it, vi } from "vitest";
+
+import type { SlackMessageEvent } from "../types.js";
+import { createSlackThreadTsResolver } from "./thread-resolution.js";
+
+describe("createSlackThreadTsResolver", () => {
+  it("caches resolved thread_ts lookups", async () => {
+    const historyMock = vi.fn().mockResolvedValue({
+      messages: [{ ts: "1", thread_ts: "9" }],
+    });
+    const resolver = createSlackThreadTsResolver({
+      client: { conversations: { history: historyMock } } as any,
+      cacheTtlMs: 60_000,
+      maxSize: 5,
+    });
+
+    const message = {
+      channel: "C1",
+      parent_user_id: "U2",
+      ts: "1",
+    } as SlackMessageEvent;
+
+    const first = await resolver.resolve({ message, source: "message" });
+    const second = await resolver.resolve({ message, source: "message" });
+
+    expect(first.thread_ts).toBe("9");
+    expect(second.thread_ts).toBe("9");
+    expect(historyMock).toHaveBeenCalledTimes(1);
+  });
+});

src/slack/monitor/thread-resolution.ts

@@ -0,0 +1,140 @@
+import type { WebClient as SlackWebClient } from "@slack/web-api";
+
+import { logVerbose, shouldLogVerbose } from "../../globals.js";
+import type { SlackMessageEvent } from "../types.js";
+
+type ThreadTsCacheEntry = {
+  threadTs: string | null;
+  updatedAt: number;
+};
+
+const DEFAULT_THREAD_TS_CACHE_TTL_MS = 60_000;
+const DEFAULT_THREAD_TS_CACHE_MAX = 500;
+
+const normalizeThreadTs = (threadTs?: string | null) => {
+  const trimmed = threadTs?.trim();
+  return trimmed ? trimmed : undefined;
+};
+
+async function resolveThreadTsFromHistory(params: {
+  client: SlackWebClient;
+  channelId: string;
+  messageTs: string;
+}) {
+  try {
+    const response = (await params.client.conversations.history({
+      channel: params.channelId,
+      latest: params.messageTs,
+      oldest: params.messageTs,
+      inclusive: true,
+      limit: 1,
+    })) as { messages?: Array<{ ts?: string; thread_ts?: string }> };
+    const message =
+      response.messages?.find((entry) => entry.ts === params.messageTs) ?? response.messages?.[0];
+    return normalizeThreadTs(message?.thread_ts);
+  } catch (err) {
+    if (shouldLogVerbose()) {
+      logVerbose(
+        `slack inbound: failed to resolve thread_ts via conversations.history for channel=${params.channelId} ts=${params.messageTs}: ${String(err)}`,
+      );
+    }
+    return undefined;
+  }
+}
+
+export function createSlackThreadTsResolver(params: {
+  client: SlackWebClient;
+  cacheTtlMs?: number;
+  maxSize?: number;
+}) {
+  const ttlMs = Math.max(0, params.cacheTtlMs ?? DEFAULT_THREAD_TS_CACHE_TTL_MS);
+  const maxSize = Math.max(0, params.maxSize ?? DEFAULT_THREAD_TS_CACHE_MAX);
+  const cache = new Map<string, ThreadTsCacheEntry>();
+  const inflight = new Map<string, Promise<string | undefined>>();
+
+  const getCached = (key: string, now: number) => {
+    const entry = cache.get(key);
+    if (!entry) return undefined;
+    if (ttlMs > 0 && now - entry.updatedAt > ttlMs) {
+      cache.delete(key);
+      return undefined;
+    }
+    cache.delete(key);
+    cache.set(key, { ...entry, updatedAt: now });
+    return entry.threadTs;
+  };
+
+  const setCached = (key: string, threadTs: string | null, now: number) => {
+    cache.delete(key);
+    cache.set(key, { threadTs, updatedAt: now });
+    if (maxSize <= 0) {
+      cache.clear();
+      return;
+    }
+    while (cache.size > maxSize) {
+      const oldestKey = cache.keys().next().value as string | undefined;
+      if (!oldestKey) break;
+      cache.delete(oldestKey);
+    }
+  };
+
+  return {
+    resolve: async (request: {
+      message: SlackMessageEvent;
+      source: "message" | "app_mention";
+    }): Promise<SlackMessageEvent> => {
+      const { message } = request;
+      if (!message.parent_user_id || message.thread_ts || !message.ts) {
+        return message;
+      }
+
+      const cacheKey = `${message.channel}:${message.ts}`;
+      const now = Date.now();
+      const cached = getCached(cacheKey, now);
+      if (cached !== undefined) {
+        return cached ? { ...message, thread_ts: cached } : message;
+      }
+
+      if (shouldLogVerbose()) {
+        logVerbose(
+          `slack inbound: missing thread_ts for thread reply channel=${message.channel} ts=${message.ts} source=${request.source}`,
+        );
+      }
+
+      let pending = inflight.get(cacheKey);
+      if (!pending) {
+        pending = resolveThreadTsFromHistory({
+          client: params.client,
+          channelId: message.channel,
+          messageTs: message.ts,
+        });
+        inflight.set(cacheKey, pending);
+      }
+
+      let resolved: string | undefined;
+      try {
+        resolved = await pending;
+      } finally {
+        inflight.delete(cacheKey);
+      }
+
+      setCached(cacheKey, resolved ?? null, Date.now());
+
+      if (resolved) {
+        if (shouldLogVerbose()) {
+          logVerbose(
+            `slack inbound: resolved missing thread_ts channel=${message.channel} ts=${message.ts} -> thread_ts=${resolved}`,
+          );
+        }
+        return { ...message, thread_ts: resolved };
+      }
+
+      if (shouldLogVerbose()) {
+        logVerbose(
+          `slack inbound: could not resolve missing thread_ts channel=${message.channel} ts=${message.ts}`,
+        );
+      }
+      return message;
+    },
+  };
+}