fix(slack): suppress reasoning in native streams

CHANGELOG.md

@@ -14,6 +14,7 @@ Docs: https://docs.openclaw.ai
 - Providers/GitHub Copilot: keep the plugin stream wrapper from claiming transport selection before OpenClaw picks a boundary-aware stream path, avoiding Pi's stale fallback Copilot headers on normal model turns. Thanks @steipete.
 - Discord/subagents: pass runtime config into thread-bound native subagent binding and require it at the helper boundary so Discord channel resolution keeps account-aware config. Fixes #71054. (#70945) Thanks @jai.
 - Slack/Assistant: accept Slack Assistant DM `message_changed` events when their metadata identifies the human sender, while continuing to drop self-authored bot edits. Fixes #55445. Thanks @AlfredPros.
+- Slack/native streaming: suppress reasoning-only payloads before `chat.startStream`/`appendStream`, so Claude extended-thinking blocks no longer appear as visible Slack messages. Fixes #59687. Thanks @vision-ifc.
 - Slack/block replies: keep multi-part block deliveries in the first Slack reply thread when `replyToMode` is `first`, matching text reply threading instead of leaking later blocks into the channel. Fixes #49341. Thanks @pholmstr and @xiwuqi.
 - Agents/failover: stop body-less HTTP 400/422 proxy failures from defaulting to `"format"` classification, so embedded retries surface the opaque provider failure instead of falling into a compaction loop. Fixes #66462. (#67024) Thanks @altaywtf and @HongzhuLiu.
 - Plugins/loader: use cached discovery-mode snapshot loads for read-only plugin capability lookups, keep snapshot caches isolated from active Gateway registries, and make same-plugin channel/HTTP route re-registration idempotent so repeated snapshot or hot-reload paths no longer rerun full plugin side effects or accumulate duplicate surfaces. Fixes #51781, #52031, #54181, and #57514. Thanks @livingghost, @okuyam2y, @ShionEria, and @bbshih.

extensions/slack/src/monitor/message-handler/dispatch.preview-fallback.test.ts

@@ -34,7 +34,13 @@ let mockedReplyThreadTs: string | undefined = THREAD_TS;
 let mockedReplyThreadTsSequence: Array<string | undefined> | undefined;
 let mockedDispatchSequence: Array<{
   kind: "tool" | "block" | "final";
-  payload: { text: string; isError?: boolean; mediaUrl?: string; mediaUrls?: string[] };
+  payload: {
+    text: string;
+    isError?: boolean;
+    isReasoning?: boolean;
+    mediaUrl?: string;
+    mediaUrls?: string[];
+  };
 }> = [];
 
 const noop = () => {};
@@ -289,7 +295,13 @@ vi.mock("../reply.runtime.js", () => ({
     replyOptions?: { disableBlockStreaming?: boolean };
     dispatcher: {
       deliver: (
-        payload: { text: string; isError?: boolean; mediaUrl?: string; mediaUrls?: string[] },
+        payload: {
+          text: string;
+          isError?: boolean;
+          isReasoning?: boolean;
+          mediaUrl?: string;
+          mediaUrls?: string[];
+        },
         info: { kind: "tool" | "block" | "final" },
       ) => Promise<void>;
     };
@@ -389,6 +401,25 @@ describe("dispatchPreparedSlackMessage preview fallback", () => {
     expect(deliverRepliesMock).not.toHaveBeenCalled();
   });
 
+  it("suppresses reasoning payloads before Slack native streaming delivery", async () => {
+    mockedNativeStreaming = true;
+    mockedDispatchSequence = [
+      { kind: "block", payload: { text: "Reasoning:\n_hidden_", isReasoning: true } },
+      { kind: "final", payload: { text: FINAL_REPLY_TEXT } },
+    ];
+
+    await dispatchPreparedSlackMessage(createPreparedSlackMessage());
+
+    expect(startSlackStreamMock).toHaveBeenCalledTimes(1);
+    expect(startSlackStreamMock).toHaveBeenCalledWith(
+      expect.objectContaining({
+        text: FINAL_REPLY_TEXT,
+      }),
+    );
+    expect(appendSlackStreamMock).not.toHaveBeenCalled();
+    expect(deliverRepliesMock).not.toHaveBeenCalled();
+  });
+
   it("keeps same-content tool and final payloads distinct after preview fallback", async () => {
     mockedDispatchSequence = [
       { kind: "tool", payload: { text: SAME_TEXT } },

extensions/slack/src/monitor/message-handler/dispatch.ts

@@ -589,6 +589,9 @@ export async function dispatchPreparedSlackMessage(prepared: PreparedSlackMessag
     payload: ReplyPayload;
     kind: ReplyDispatchKind;
   }): Promise<void> => {
+    if (params.payload.isReasoning === true) {
+      return;
+    }
     const reply = resolveSendableOutboundReplyParts(params.payload);
     if (
       streamFailed ||