fix(slack): suppress block streaming during previews

CHANGELOG.md

@@ -67,6 +67,7 @@ Docs: https://docs.openclaw.ai
 - Plugin SDK/tool-result transforms: bound middleware `details`, validate in-place result mutations, and mark fail-closed middleware fallbacks with canonical `error` status. Thanks @vincentkoc.
 - Discord/gateway: prevent startup from getting stuck at `awaiting gateway readiness` when Carbon gateway registration races with a lifecycle reconnect. Fixes #52372. (#68159) Thanks @IVY-AI-gif.
 - Discord/gateway: supervise Carbon's async gateway registration promise so fatal Discord metadata failures surface through startup instead of process-level unhandled rejections. (#62451) Thanks @safzanpirani.
+- Slack/streaming: suppress block replies while native or draft preview streaming owns the turn, preventing duplicate Slack delivery when block streaming is also enabled. Addresses #56675. Thanks @hsiaoa.
 - Plugins/cache: restore plugin command and interactive handler registries on loader cache hits without resetting interactive callback dedupe, so cached external plugins keep slash commands and callback handlers available after reloads. Fixes #71100. Thanks @BomBastikDE.
 - Gateway/OpenAI-compatible: report non-zero token usage for `/v1/chat/completions` when the agent run has only last-call usage metadata available. Fixes #71118. (#71242) Thanks @RenzoMXD.
 - Plugin SDK/tool-result transforms: restrict harness tool-result middleware to bundled plugins, fail closed on middleware errors, validate rewritten result shapes, preserve Pi per-call ids, and keep Codex media trust checks anchored to raw tool provenance. Thanks @vincentkoc.

docs/concepts/streaming.md

@@ -156,6 +156,7 @@ Slack:
 - `partial` can use Slack native streaming (`chat.startStream`/`append`/`stop`) when available.
 - `block` uses append-style draft previews.
 - `progress` uses status preview text, then final answer.
+- Native and draft preview streaming suppress block replies for that turn, so a Slack reply is streamed by one delivery path only.
 - Final media/error payloads and progress finals do not create throwaway draft messages; only text/block finals that can edit the preview flush pending draft text.
 
 Mattermost:

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

@@ -28,6 +28,8 @@ class TestSlackStreamNotDeliveredError extends Error {
   }
 }
 let mockedNativeStreaming = false;
+let mockedBlockStreamingEnabled: boolean | undefined = false;
+let capturedReplyOptions: { disableBlockStreaming?: boolean } | undefined;
 let mockedDispatchSequence: Array<{
   kind: "tool" | "block" | "final";
   payload: { text: string; isError?: boolean; mediaUrl?: string; mediaUrls?: string[] };
@@ -129,7 +131,7 @@ vi.mock("openclaw/plugin-sdk/channel-reply-pipeline", () => ({
 }));
 
 vi.mock("openclaw/plugin-sdk/channel-streaming", () => ({
-  resolveChannelStreamingBlockEnabled: () => false,
+  resolveChannelStreamingBlockEnabled: () => mockedBlockStreamingEnabled,
   resolveChannelStreamingNativeTransport: () => mockedNativeStreaming,
   resolveChannelStreamingPreviewToolProgress: () => true,
 }));
@@ -266,6 +268,7 @@ vi.mock("../reply.runtime.js", () => ({
     markDispatchIdle: () => {},
   }),
   dispatchInboundMessage: async (params: {
+    replyOptions?: { disableBlockStreaming?: boolean };
     dispatcher: {
       deliver: (
         payload: { text: string; isError?: boolean; mediaUrl?: string; mediaUrls?: string[] },
@@ -273,6 +276,7 @@ vi.mock("../reply.runtime.js", () => ({
       ) => Promise<void>;
     };
   }) => {
+    capturedReplyOptions = params.replyOptions;
     for (const entry of mockedDispatchSequence) {
       await params.dispatcher.deliver(entry.payload, { kind: entry.kind });
     }
@@ -305,6 +309,8 @@ describe("dispatchPreparedSlackMessage preview fallback", () => {
     startSlackStreamMock.mockReset();
     stopSlackStreamMock.mockReset();
     mockedNativeStreaming = false;
+    mockedBlockStreamingEnabled = false;
+    capturedReplyOptions = undefined;
     mockedDispatchSequence = [{ kind: "final", payload: { text: FINAL_REPLY_TEXT } }];
 
     createSlackDraftStreamMock.mockReturnValue(createDraftStreamStub());
@@ -333,6 +339,14 @@ describe("dispatchPreparedSlackMessage preview fallback", () => {
     );
   });
 
+  it("suppresses block streaming when Slack draft preview streaming is active", async () => {
+    mockedBlockStreamingEnabled = true;
+
+    await dispatchPreparedSlackMessage(createPreparedSlackMessage());
+
+    expect(capturedReplyOptions?.disableBlockStreaming).toBe(true);
+  });
+
   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.streaming.test.ts

@@ -2,6 +2,7 @@ import { describe, expect, it, vi } from "vitest";
 import {
   createSlackTurnDeliveryTracker,
   isSlackStreamingEnabled,
+  resolveSlackDisableBlockStreaming,
   resolveSlackStreamRecipientTeamId,
   resolveSlackStreamingThreadHint,
   shouldEnableSlackPreviewStreaming,
@@ -242,3 +243,52 @@ describe("slack draft stream initialization", () => {
     ).toBe(true);
   });
 });
+
+describe("slack block streaming suppression", () => {
+  it("disables block streaming when native Slack streaming is active", () => {
+    expect(
+      resolveSlackDisableBlockStreaming({
+        useStreaming: true,
+        shouldUseDraftStream: false,
+        blockStreamingEnabled: true,
+      }),
+    ).toBe(true);
+  });
+
+  it("disables block streaming when draft preview streaming is active", () => {
+    expect(
+      resolveSlackDisableBlockStreaming({
+        useStreaming: false,
+        shouldUseDraftStream: true,
+        blockStreamingEnabled: true,
+      }),
+    ).toBe(true);
+  });
+
+  it("respects explicit block streaming config when preview streaming is inactive", () => {
+    expect(
+      resolveSlackDisableBlockStreaming({
+        useStreaming: false,
+        shouldUseDraftStream: false,
+        blockStreamingEnabled: true,
+      }),
+    ).toBe(false);
+    expect(
+      resolveSlackDisableBlockStreaming({
+        useStreaming: false,
+        shouldUseDraftStream: false,
+        blockStreamingEnabled: false,
+      }),
+    ).toBe(true);
+  });
+
+  it("leaves block streaming policy unset when no channel override exists", () => {
+    expect(
+      resolveSlackDisableBlockStreaming({
+        useStreaming: false,
+        shouldUseDraftStream: false,
+        blockStreamingEnabled: undefined,
+      }),
+    ).toBeUndefined();
+  });
+});

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

@@ -121,6 +121,19 @@ export function shouldInitializeSlackDraftStream(params: {
   return params.previewStreamingEnabled && !params.useStreaming;
 }
 
+export function resolveSlackDisableBlockStreaming(params: {
+  useStreaming: boolean;
+  shouldUseDraftStream: boolean;
+  blockStreamingEnabled: boolean | undefined;
+}): boolean | undefined {
+  if (params.useStreaming || params.shouldUseDraftStream) {
+    return true;
+  }
+  return typeof params.blockStreamingEnabled === "boolean"
+    ? !params.blockStreamingEnabled
+    : undefined;
+}
+
 export function resolveSlackStreamingThreadHint(params: {
   replyToMode: "off" | "first" | "all" | "batched";
   incomingThreadTs: string | undefined;
@@ -426,6 +439,12 @@ export async function dispatchPreparedSlackMessage(prepared: PreparedSlackMessag
     previewStreamingEnabled,
     useStreaming,
   });
+  const blockStreamingEnabled = resolveChannelStreamingBlockEnabled(account.config);
+  const disableBlockStreaming = resolveSlackDisableBlockStreaming({
+    useStreaming,
+    shouldUseDraftStream,
+    blockStreamingEnabled,
+  });
   let streamSession: SlackStreamSession | null = null;
   let streamFailed = false;
   let usedReplyThreadTs: string | undefined;
@@ -909,11 +928,7 @@ export async function dispatchPreparedSlackMessage(prepared: PreparedSlackMessag
         ...replyOptions,
         skillFilter: prepared.channelConfig?.skills,
         hasRepliedRef,
-        disableBlockStreaming: useStreaming
-          ? true
-          : typeof resolveChannelStreamingBlockEnabled(account.config) === "boolean"
-            ? !resolveChannelStreamingBlockEnabled(account.config)
-            : undefined,
+        disableBlockStreaming,
         onModelSelected,
         suppressDefaultToolProgressMessages: previewToolProgressEnabled ? true : undefined,
         onPartialReply: useStreaming