fix: scope messageThreadId override to DM assistant threads only

zozo123 · claude · zozo123 · commit 2ca2221a0aa3 · 2026-04-12T10:59:03.000+03:00
The previous fix unconditionally set messageThreadId when hasThreadTs was
true, which affected channel/group messages where thread_ts == ts (auto-
created top-level threads). This caused buildSlackThreadingToolContext to
force replyToMode to "all" in non-DM contexts, unexpectedly routing tool
and subagent outputs into threads.

Now the override only applies when channel_type is "im", correctly
limiting it to the Slack Agents &amp; Assistants DM root-message scenario.

Co-Authored-By: Claude Opus 4.6 &lt;noreply@anthropic.com&gt;
diff --git a/extensions/slack/src/threading.test.ts b/extensions/slack/src/threading.test.ts
@@ -88,26 +88,48 @@ describe("resolveSlackThreadTargets", () => {
     expect(context.replyToId).toBe("123");
   });
 
-  it("sets messageThreadId for thread-root messages regardless of replyToMode", () => {
+  it("sets messageThreadId for DM assistant thread-root messages regardless of replyToMode", () => {
     for (const replyToMode of ["off", "first", "batched"] as const) {
       const context = resolveSlackThreadContext({
         replyToMode,
         message: {
           type: "message",
-          channel: "C1",
+          channel: "D1",
+          channel_type: "im",
           ts: "123",
           thread_ts: "123",
         },
       });
 
       expect(context.isThreadReply).toBe(false);
-      // thread_ts == ts: Agents & Assistants DM root — preserve thread context
-      // so tool calls (subagent results) thread correctly regardless of mode.
+      // thread_ts == ts in a DM: Agents & Assistants root — preserve thread
+      // context so tool calls (subagent results) thread correctly.
       expect(context.messageThreadId).toBe("123");
       expect(context.replyToId).toBe("123");
     }
   });
 
+  it("does not set messageThreadId for channel thread-root messages with non-all replyToMode", () => {
+    for (const replyToMode of ["off", "first", "batched"] as const) {
+      const context = resolveSlackThreadContext({
+        replyToMode,
+        message: {
+          type: "message",
+          channel: "C1",
+          channel_type: "channel",
+          ts: "123",
+          thread_ts: "123",
+        },
+      });
+
+      expect(context.isThreadReply).toBe(false);
+      // thread_ts == ts in a channel: auto-created top-level thread_ts should
+      // NOT force threaded mode — only DM assistant threads get the override.
+      expect(context.messageThreadId).toBeUndefined();
+      expect(context.replyToId).toBe("123");
+    }
+  });
+
   it("prefers thread_ts as messageThreadId for replies", () => {
     const context = resolveSlackThreadContext({
       replyToMode: "off",
diff --git a/extensions/slack/src/threading.ts b/extensions/slack/src/threading.ts
@@ -20,15 +20,21 @@ export function resolveSlackThreadContext(params: {
   const isThreadReply =
     hasThreadTs && (incomingThreadTs !== messageTs || Boolean(params.message.parent_user_id));
   const replyToId = incomingThreadTs ?? messageTs;
-  // Preserve thread context for thread replies AND for thread-root messages
-  // (e.g. Slack Agents & Assistants DMs where thread_ts == ts on the initial
+  // Preserve thread context for DM assistant thread-root messages
+  // (Slack Agents & Assistants DMs where thread_ts == ts on the initial
   // message). Without this, tool calls that run during the same turn (subagent
   // results) lose the thread identifier after the first reply because
   // hasRepliedRef gets marked true, causing subsequent sendMessage calls to fall
   // through to the top-level channel.
+  // Only apply for DM (im) channels — in channels/groups, an auto-created
+  // thread_ts == ts must not force threaded mode, since downstream
+  // buildSlackThreadingToolContext treats any MessageThreadId as an explicit
+  // thread target and overrides replyToMode to "all".
+  const isDmAssistantThread =
+    hasThreadTs && !isThreadReply && params.message.channel_type === "im";
   const messageThreadId = isThreadReply
     ? incomingThreadTs
-    : hasThreadTs
+    : isDmAssistantThread
       ? incomingThreadTs
       : params.replyToMode === "all"
         ? messageTs
