diff --git a/extensions/slack/src/monitor.failure-notices.test.ts b/extensions/slack/src/monitor.failure-notices.test.ts
new file mode 100644
index 000000000000..2cee9bff9122
--- /dev/null
+++ b/extensions/slack/src/monitor.failure-notices.test.ts
@@ -0,0 +1,328 @@
+import type { OpenKeyedStoreOptions } from "openclaw/plugin-sdk/plugin-state-runtime";
+import { createPluginStateKeyedStoreForTests } from "openclaw/plugin-sdk/plugin-state-test-runtime";
+import { setReplyPayloadMetadata } from "openclaw/plugin-sdk/reply-payload-testing";
+import { resetInboundDedupe } from "openclaw/plugin-sdk/reply-runtime";
+import { beforeEach, describe, expect, it } from "vitest";
+import {
+  getSlackTestState,
+  resetSlackTestState,
+  runSlackMessageOnce,
+} from "./monitor.test-helpers.js";
+import { getSlackRuntime, setSlackRuntime } from "./runtime.js";
+import {
+  clearSlackThreadParticipationCache,
+  hasSlackThreadParticipation,
+} from "./sent-thread-cache.js";
+
+const { monitorSlackProvider } = await import("./monitor/provider.js");
+const slackTestState = getSlackTestState();
+const AUTH_FAILURE = "⚠️ Model login expired on the gateway.";
+const BACKEND_FAILURE = "⚠️ Codex app-server is unavailable.";
+
+type SlackFailureTestEvent = {
+  type: "message";
+  user: string;
+  text: string;
+  ts: string;
+  channel: string;
+  channel_type: "im" | "mpim" | "channel";
+  thread_ts?: string;
+  parent_user_id?: string;
+};
+
+function makeEvent(overrides: Partial<SlackFailureTestEvent>): SlackFailureTestEvent {
+  return {
+    type: "message",
+    user: "U1",
+    text: "ordinary follow-up",
+    ts: "100.000001",
+    channel: "C1",
+    channel_type: "channel",
+    ...overrides,
+  };
+}
+
+async function dispatchEvent(overrides: Partial<SlackFailureTestEvent>): Promise<void> {
+  await runSlackMessageOnce(
+    monitorSlackProvider,
+    { event: makeEvent(overrides) },
+    { awaitDispatch: true },
+  );
+}
+
+function mockReplySequence(...payloads: Array<{ text: string; isError?: boolean }>): void {
+  let runIndex = 0;
+  slackTestState.replyMock.mockImplementation(async (...args: unknown[]) => {
+    const options = args[1] as { onAgentRunStart?: (runId: string) => void } | undefined;
+    options?.onAgentRunStart?.(`slack-failure-notice-test-${runIndex}`);
+    const payload = payloads[Math.min(runIndex, payloads.length - 1)];
+    runIndex += 1;
+    return payload;
+  });
+}
+
+function enableAmbientChannelReplies(replyToMode: "all" | "off" = "all"): void {
+  slackTestState.config = {
+    messages: { groupChat: { visibleReplies: "automatic" } },
+    channels: {
+      slack: {
+        dm: { enabled: true },
+        dmPolicy: "open",
+        allowFrom: ["*"],
+        groupPolicy: "open",
+        requireMention: false,
+        replyToMode,
+        channels: { C1: { allow: true, requireMention: false } },
+      },
+    },
+  };
+}
+
+describe("Slack thread failure notices", () => {
+  beforeEach(() => {
+    resetInboundDedupe();
+    clearSlackThreadParticipationCache();
+    resetSlackTestState({
+      messages: { groupChat: { visibleReplies: "automatic" } },
+      channels: {
+        slack: {
+          dm: { enabled: true },
+          dmPolicy: "open",
+          allowFrom: ["*"],
+          groupPolicy: "open",
+          requireMention: true,
+          replyToMode: "all",
+          channels: { C1: { allow: true, requireMention: true } },
+        },
+      },
+    });
+  });
+
+  it("shows an explicit mention's failure and suppresses matching passive follow-ups", async () => {
+    mockReplySequence({ text: AUTH_FAILURE, isError: true });
+
+    await dispatchEvent({ text: "<@bot-user> please help", ts: "100.000000" });
+    await dispatchEvent({ ts: "100.000001", thread_ts: "100.000000", parent_user_id: "U1" });
+    await dispatchEvent({ ts: "100.000002", thread_ts: "100.000000", parent_user_id: "U1" });
+
+    expect(slackTestState.replyMock).toHaveBeenCalledTimes(3);
+    expect(slackTestState.sendMock).toHaveBeenCalledTimes(1);
+  });
+
+  it("announces the first failure after an established thread was working", async () => {
+    mockReplySequence({ text: "Working normally" }, { text: AUTH_FAILURE, isError: true });
+
+    await dispatchEvent({ text: "<@bot-user> please help", ts: "101.000000" });
+    await dispatchEvent({ ts: "101.000001", thread_ts: "101.000000", parent_user_id: "U1" });
+    await dispatchEvent({ ts: "101.000002", thread_ts: "101.000000", parent_user_id: "U1" });
+
+    expect(slackTestState.sendMock).toHaveBeenCalledTimes(2);
+    expect(slackTestState.sendMock.mock.calls[1]?.[1]).toBe(AUTH_FAILURE);
+  });
+
+  it("announces the first failure for participation restored after a restart", async () => {
+    const threadTs = "101.100000";
+    const openKeyedStore = <T>(options: OpenKeyedStoreOptions) =>
+      createPluginStateKeyedStoreForTests<T>("slack", options);
+    const persistedStore = openKeyedStore<{ repliedAt: number }>({
+      namespace: "slack.thread-participation",
+      maxEntries: 1000,
+    });
+    await persistedStore.register(
+      `default:C1:${threadTs}`,
+      { repliedAt: Date.now() },
+      {
+        ttlMs: 60_000,
+      },
+    );
+    const runtime = getSlackRuntime();
+    setSlackRuntime({
+      ...runtime,
+      state: {
+        ...runtime.state,
+        openKeyedStore,
+      },
+    });
+    expect(hasSlackThreadParticipation("default", "C1", threadTs)).toBe(false);
+    mockReplySequence({ text: AUTH_FAILURE, isError: true });
+
+    await dispatchEvent({ ts: "101.100001", thread_ts: threadTs, parent_user_id: "U1" });
+    await dispatchEvent({ ts: "101.100002", thread_ts: threadTs, parent_user_id: "U1" });
+
+    expect(slackTestState.replyMock).toHaveBeenCalledTimes(2);
+    expect(slackTestState.sendMock).toHaveBeenCalledTimes(1);
+    expect(slackTestState.sendMock.mock.calls[0]?.[1]).toBe(AUTH_FAILURE);
+  });
+
+  it("announces a different failure after suppressing repeated copies of the first", async () => {
+    mockReplySequence(
+      { text: "Working normally" },
+      { text: AUTH_FAILURE, isError: true },
+      { text: AUTH_FAILURE, isError: true },
+      { text: BACKEND_FAILURE, isError: true },
+    );
+
+    await dispatchEvent({ text: "<@bot-user> please help", ts: "102.000000" });
+    await dispatchEvent({ ts: "102.000001", thread_ts: "102.000000", parent_user_id: "U1" });
+    await dispatchEvent({ ts: "102.000002", thread_ts: "102.000000", parent_user_id: "U1" });
+    await dispatchEvent({ ts: "102.000003", thread_ts: "102.000000", parent_user_id: "U1" });
+
+    expect(slackTestState.sendMock).toHaveBeenCalledTimes(3);
+    expect(slackTestState.sendMock.mock.calls[2]?.[1]).toBe(BACKEND_FAILURE);
+  });
+
+  it("announces the same failure again after a successful reply", async () => {
+    mockReplySequence(
+      { text: "Working normally" },
+      { text: AUTH_FAILURE, isError: true },
+      { text: "Recovered" },
+      { text: AUTH_FAILURE, isError: true },
+    );
+
+    await dispatchEvent({ text: "<@bot-user> please help", ts: "103.000000" });
+    await dispatchEvent({ ts: "103.000001", thread_ts: "103.000000", parent_user_id: "U1" });
+    await dispatchEvent({ ts: "103.000002", thread_ts: "103.000000", parent_user_id: "U1" });
+    await dispatchEvent({ ts: "103.000003", thread_ts: "103.000000", parent_user_id: "U1" });
+
+    expect(slackTestState.sendMock).toHaveBeenCalledTimes(4);
+    expect(slackTestState.sendMock.mock.calls[3]?.[1]).toBe(AUTH_FAILURE);
+  });
+
+  it("always explains the current failure when the user explicitly mentions the bot", async () => {
+    mockReplySequence({ text: AUTH_FAILURE, isError: true });
+
+    await dispatchEvent({ text: "<@bot-user> please help", ts: "104.000000" });
+    await dispatchEvent({ ts: "104.000001", thread_ts: "104.000000", parent_user_id: "U1" });
+    await dispatchEvent({
+      text: "<@bot-user> are you working now?",
+      ts: "104.000002",
+      thread_ts: "104.000000",
+      parent_user_id: "U1",
+    });
+
+    expect(slackTestState.sendMock).toHaveBeenCalledTimes(2);
+  });
+
+  it.each(["all", "off"] as const)(
+    "announces one failure for unmentioned channel messages with reply mode %s",
+    async (replyToMode) => {
+      enableAmbientChannelReplies(replyToMode);
+      mockReplySequence({ text: AUTH_FAILURE, isError: true });
+
+      await dispatchEvent({ ts: "105.000000" });
+      await dispatchEvent({ ts: "105.000001" });
+
+      expect(slackTestState.replyMock).toHaveBeenCalledTimes(2);
+      expect(slackTestState.sendMock).toHaveBeenCalledTimes(1);
+      expect(slackTestState.sendMock.mock.calls[0]?.[1]).toBe(AUTH_FAILURE);
+    },
+  );
+
+  it("announces a changed failure for unmentioned channel messages", async () => {
+    enableAmbientChannelReplies();
+    mockReplySequence(
+      { text: AUTH_FAILURE, isError: true },
+      { text: AUTH_FAILURE, isError: true },
+      { text: BACKEND_FAILURE, isError: true },
+    );
+
+    await dispatchEvent({ ts: "105.010000" });
+    await dispatchEvent({ ts: "105.010001" });
+    await dispatchEvent({ ts: "105.010002" });
+
+    expect(slackTestState.sendMock).toHaveBeenCalledTimes(2);
+    expect(slackTestState.sendMock.mock.calls[1]?.[1]).toBe(BACKEND_FAILURE);
+  });
+
+  it("announces an unmentioned channel failure again after a successful reply", async () => {
+    enableAmbientChannelReplies();
+    mockReplySequence(
+      { text: AUTH_FAILURE, isError: true },
+      { text: AUTH_FAILURE, isError: true },
+      { text: "Recovered" },
+      { text: AUTH_FAILURE, isError: true },
+    );
+
+    await dispatchEvent({ ts: "105.020000" });
+    await dispatchEvent({ ts: "105.020001" });
+    await dispatchEvent({ ts: "105.020002" });
+    await dispatchEvent({ ts: "105.020003" });
+
+    expect(slackTestState.sendMock).toHaveBeenCalledTimes(3);
+    expect(slackTestState.sendMock.mock.calls[2]?.[1]).toBe(AUTH_FAILURE);
+  });
+
+  it("always answers an explicit mention after an unmentioned channel failure", async () => {
+    enableAmbientChannelReplies();
+    mockReplySequence({ text: AUTH_FAILURE, isError: true });
+
+    await dispatchEvent({ ts: "105.030000" });
+    await dispatchEvent({ ts: "105.030001" });
+    await dispatchEvent({ text: "<@bot-user> are you working now?", ts: "105.030002" });
+
+    expect(slackTestState.sendMock).toHaveBeenCalledTimes(2);
+    expect(slackTestState.sendMock.mock.calls[1]?.[1]).toBe(AUTH_FAILURE);
+  });
+
+  it("retries the same thread failure when its first Slack delivery fails", async () => {
+    mockReplySequence(
+      { text: "Working normally" },
+      { text: AUTH_FAILURE, isError: true },
+      { text: AUTH_FAILURE, isError: true },
+    );
+
+    await dispatchEvent({ text: "<@bot-user> please help", ts: "105.040000" });
+    slackTestState.sendMock.mockRejectedValueOnce(new Error("Slack delivery unavailable"));
+
+    await dispatchEvent({ ts: "105.040001", thread_ts: "105.040000", parent_user_id: "U1" });
+    await dispatchEvent({ ts: "105.040002", thread_ts: "105.040000", parent_user_id: "U1" });
+
+    expect(slackTestState.sendMock).toHaveBeenCalledTimes(3);
+    expect(slackTestState.sendMock.mock.calls[2]?.[1]).toBe(AUTH_FAILURE);
+  });
+
+  it("does not suppress warnings for non-terminal tool failures", async () => {
+    const warning = setReplyPayloadMetadata(
+      { text: "A tool failed, but the run completed.", isError: true },
+      { nonTerminalToolErrorWarning: true },
+    );
+    mockReplySequence({ text: "Working normally" }, warning, warning);
+
+    await dispatchEvent({ text: "<@bot-user> please help", ts: "105.100000" });
+    await dispatchEvent({ ts: "105.100001", thread_ts: "105.100000", parent_user_id: "U1" });
+    await dispatchEvent({ ts: "105.100002", thread_ts: "105.100000", parent_user_id: "U1" });
+
+    expect(slackTestState.sendMock).toHaveBeenCalledTimes(3);
+  });
+
+  it("keeps failures visible in direct messages", async () => {
+    mockReplySequence({ text: AUTH_FAILURE, isError: true });
+
+    await dispatchEvent({ channel: "D1", channel_type: "im", ts: "106.000000" });
+    await dispatchEvent({ channel: "D1", channel_type: "im", ts: "106.000001" });
+
+    expect(slackTestState.sendMock).toHaveBeenCalledTimes(2);
+  });
+
+  it("keeps failures visible in Slack group direct messages", async () => {
+    slackTestState.config = {
+      messages: { groupChat: { visibleReplies: "automatic" } },
+      channels: {
+        slack: {
+          dm: { enabled: true, groupEnabled: true },
+          dmPolicy: "open",
+          allowFrom: ["U1"],
+          groupPolicy: "open",
+          replyToMode: "off",
+        },
+      },
+    };
+    mockReplySequence({ text: AUTH_FAILURE, isError: true });
+
+    await dispatchEvent({ channel: "G1", channel_type: "mpim", ts: "107.000000" });
+    await dispatchEvent({ channel: "G1", channel_type: "mpim", ts: "107.000001" });
+
+    expect(slackTestState.replyMock).toHaveBeenCalledTimes(2);
+    expect(slackTestState.sendMock).toHaveBeenCalledTimes(2);
+  });
+});
diff --git a/extensions/slack/src/monitor/message-handler/dispatch.preview-fallback.test.ts b/extensions/slack/src/monitor/message-handler/dispatch.preview-fallback.test.ts
index 246d1a156fbd..efe5af1b829c 100644
--- a/extensions/slack/src/monitor/message-handler/dispatch.preview-fallback.test.ts
+++ b/extensions/slack/src/monitor/message-handler/dispatch.preview-fallback.test.ts
@@ -810,6 +810,7 @@ vi.mock("openclaw/plugin-sdk/reply-history", () => ({
 }));
 
 vi.mock("openclaw/plugin-sdk/reply-payload", () => ({
+  isReplyPayloadNonTerminalToolErrorWarning: () => false,
   buildTtsSupplementMediaPayload: (payload: {
     text?: string;
     mediaUrl?: string;
@@ -900,6 +901,9 @@ vi.mock("../../limits.js", () => ({
 }));
 
 vi.mock("../../sent-thread-cache.js", () => ({
+  clearSlackThreadFailureNotice: () => {},
+  hasSlackThreadParticipation: () => false,
+  recordSlackThreadFailureNotice: () => true,
   recordSlackThreadParticipation: recordSlackThreadParticipationMock,
 }));
 
diff --git a/extensions/slack/src/monitor/message-handler/dispatch.ts b/extensions/slack/src/monitor/message-handler/dispatch.ts
index 39aa90b06e0e..f23f9ade010a 100644
--- a/extensions/slack/src/monitor/message-handler/dispatch.ts
+++ b/extensions/slack/src/monitor/message-handler/dispatch.ts
@@ -14,6 +14,7 @@ import { toErrorObject } from "openclaw/plugin-sdk/error-runtime";
 import {
   buildTtsSupplementMediaPayload,
   getReplyPayloadTtsSupplement,
+  isReplyPayloadNonTerminalToolErrorWarning,
   resolveSendableOutboundReplyParts,
 } from "openclaw/plugin-sdk/reply-payload";
 import type { ReplyPayload } from "openclaw/plugin-sdk/reply-runtime";
@@ -24,7 +25,13 @@ import { normalizeSlackOutboundText } from "../../format.js";
 import { SLACK_EDIT_TEXT_MAX_BYTES } from "../../limits.js";
 import { emitSlackMessageSentHooks } from "../../message-sent-hook.js";
 import { resolveSlackReplyRenderPlan } from "../../reply-blocks.js";
-import { recordSlackThreadParticipation } from "../../sent-thread-cache.js";
+import {
+  clearSlackThreadFailureNotice,
+  hasSlackThreadFailureNotice,
+  hasSlackThreadParticipation,
+  recordSlackThreadFailureNotice,
+  recordSlackThreadParticipation,
+} from "../../sent-thread-cache.js";
 import {
   SlackStreamNotDeliveredError,
   stopSlackStream,
@@ -78,6 +85,73 @@ export async function dispatchPreparedSlackMessage(prepared: PreparedSlackMessag
     },
   });
   const draftStream = progress.draftStream;
+  const failureNoticeThreadTs = message.thread_ts;
+  const failureNoticeTeamId = prepared.eventScope?.teamId;
+  let sawTerminalFailurePayload = false;
+  let pendingFailureNotice:
+    | {
+        accountId: string;
+        channelId: string;
+        threadTs?: string;
+        failureText: string;
+        teamId?: string;
+      }
+    | undefined;
+
+  const filterPassiveThreadFailure = (payload: ReplyPayload): ReplyPayload | null => {
+    if (
+      payload.isError !== true ||
+      prepared.ctxPayload.ChatType !== "channel" ||
+      isReplyPayloadNonTerminalToolErrorWarning(payload)
+    ) {
+      return payload;
+    }
+    sawTerminalFailurePayload = true;
+    if (delivery.observedReplyDelivery || draftPreviewCommitted.value) {
+      return payload;
+    }
+
+    const explicitlyAddressed =
+      prepared.ctxPayload.ExplicitlyMentionedBot === true ||
+      prepared.ctxPayload.MentionSource === "explicit_bot" ||
+      prepared.ctxPayload.MentionSource === "subteam" ||
+      prepared.ctxPayload.MentionSource === "mention_pattern" ||
+      prepared.ctxPayload.MentionSource === "command_bypass" ||
+      (prepared.ctxPayload.CommandTurn?.kind !== undefined &&
+        prepared.ctxPayload.CommandTurn.kind !== "normal" &&
+        prepared.ctxPayload.CommandTurn.authorized);
+    const noticeThreadTs =
+      failureNoticeThreadTs ?? (explicitlyAddressed ? statusThreadTs : undefined);
+
+    const notice = {
+      accountId: account.accountId,
+      channelId: message.channel,
+      ...(noticeThreadTs ? { threadTs: noticeThreadTs } : {}),
+      failureText: payload.text ?? "",
+      ...(failureNoticeTeamId ? { teamId: failureNoticeTeamId } : {}),
+    };
+    if (
+      failureNoticeThreadTs &&
+      !explicitlyAddressed &&
+      prepared.ctxPayload.MentionSource !== "implicit_thread" &&
+      !hasSlackThreadParticipation(
+        notice.accountId,
+        notice.channelId,
+        failureNoticeThreadTs,
+        failureNoticeTeamId,
+      )
+    ) {
+      logVerbose("slack: suppressed passive failure before thread participation");
+      return null;
+    }
+
+    if (!explicitlyAddressed && hasSlackThreadFailureNotice(notice)) {
+      logVerbose("slack: suppressed repeated passive channel or thread failure");
+      return null;
+    }
+    pendingFailureNotice = notice;
+    return payload;
+  };
 
   const deliverSlackPayload = async (
     payload: ReplyPayload,
@@ -385,6 +459,13 @@ export async function dispatchPreparedSlackMessage(prepared: PreparedSlackMessag
       ctxPayload: prepared.ctxPayload,
       dispatcherOptions: {
         ...replyPipeline,
+        // A channel transform marks intentional silence before core can synthesize an empty-reply error.
+        transformReplyPayload: (payload) => {
+          const transformed = replyPipeline.transformReplyPayload
+            ? replyPipeline.transformReplyPayload(payload)
+            : payload;
+          return transformed ? filterPassiveThreadFailure(transformed) : null;
+        },
         humanDelay: resolveHumanDelayConfig(cfg, route.agentId),
       },
       delivery: {
@@ -511,7 +592,20 @@ export async function dispatchPreparedSlackMessage(prepared: PreparedSlackMessag
       const result = turnResult.dispatchResult;
       queuedFinal = result.queuedFinal;
       counts = result.counts;
-      agentRunFailed = readAgentRunTerminalOutcome(result) === "failed";
+      const agentRunOutcome = readAgentRunTerminalOutcome(result);
+      agentRunFailed = agentRunOutcome === "failed";
+      if (
+        agentRunOutcome === "completed" &&
+        !sawTerminalFailurePayload &&
+        prepared.ctxPayload.ChatType === "channel"
+      ) {
+        clearSlackThreadFailureNotice({
+          accountId: account.accountId,
+          channelId: message.channel,
+          ...(failureNoticeThreadTs ? { threadTs: failureNoticeThreadTs } : {}),
+          ...(failureNoticeTeamId ? { teamId: failureNoticeTeamId } : {}),
+        });
+      }
     }
   } catch (err) {
     dispatchError = err;
@@ -590,6 +684,10 @@ export async function dispatchPreparedSlackMessage(prepared: PreparedSlackMessag
     },
   );
 
+  if (pendingFailureNotice && anyReplyDelivered) {
+    recordSlackThreadFailureNotice(pendingFailureNotice);
+  }
+
   if (dispatchError || agentRunFailed) {
     await progress.finalizeDraftProgressCard("error");
   }
diff --git a/extensions/slack/src/sent-thread-cache.test.ts b/extensions/slack/src/sent-thread-cache.test.ts
index 808972bcc599..56e6144a575a 100644
--- a/extensions/slack/src/sent-thread-cache.test.ts
+++ b/extensions/slack/src/sent-thread-cache.test.ts
@@ -9,9 +9,12 @@ import { withOpenClawTestState } from "openclaw/plugin-sdk/test-state";
 import { afterEach, describe, expect, it, vi } from "vitest";
 import { setSlackRuntime } from "./runtime.js";
 import {
+  clearSlackThreadFailureNotice,
   clearSlackThreadParticipationCache,
+  hasSlackThreadFailureNotice,
   hasSlackThreadParticipation,
   hasSlackThreadParticipationWithPersistence,
+  recordSlackThreadFailureNotice,
   recordSlackThreadParticipation,
 } from "./sent-thread-cache.js";
 
@@ -52,6 +55,142 @@ describe("slack sent-thread-cache", () => {
     expect(hasSlackThreadParticipation("A1", "C123", "1700000000.000001")).toBe(false);
   });
 
+  it("announces a repeated thread failure only once until its message changes", () => {
+    const notice = {
+      accountId: "A1",
+      channelId: "C123",
+      threadTs: "1700000000.000001",
+      failureText: "Model login expired",
+    };
+
+    expect(recordSlackThreadFailureNotice(notice)).toBe(true);
+    expect(recordSlackThreadFailureNotice(notice)).toBe(false);
+    expect(
+      recordSlackThreadFailureNotice({ ...notice, failureText: "Model   login\nexpired" }),
+    ).toBe(false);
+    expect(
+      recordSlackThreadFailureNotice({ ...notice, failureText: "App server unavailable" }),
+    ).toBe(true);
+    expect(recordSlackThreadFailureNotice(notice)).toBe(true);
+  });
+
+  it("checks a failure without marking it delivered", () => {
+    const notice = {
+      accountId: "A1",
+      channelId: "C123",
+      threadTs: "1700000000.000001",
+      failureText: "Model login expired",
+    };
+
+    expect(hasSlackThreadFailureNotice(notice)).toBe(false);
+    expect(hasSlackThreadFailureNotice(notice)).toBe(false);
+    expect(recordSlackThreadFailureNotice(notice)).toBe(true);
+    expect(hasSlackThreadFailureNotice(notice)).toBe(true);
+    expect(hasSlackThreadFailureNotice({ ...notice, failureText: "Model  login\nexpired" })).toBe(
+      true,
+    );
+    expect(hasSlackThreadFailureNotice({ ...notice, failureText: "App server unavailable" })).toBe(
+      false,
+    );
+  });
+
+  it("deduplicates top-level failures per channel without mixing them with threads", () => {
+    const channelNotice = {
+      accountId: "A1",
+      channelId: "C123",
+      failureText: "Model login expired",
+      teamId: "T1",
+    };
+
+    expect(hasSlackThreadFailureNotice(channelNotice)).toBe(false);
+    expect(recordSlackThreadFailureNotice(channelNotice)).toBe(true);
+    expect(hasSlackThreadFailureNotice(channelNotice)).toBe(true);
+    expect(recordSlackThreadFailureNotice(channelNotice)).toBe(false);
+    expect(hasSlackThreadFailureNotice({ ...channelNotice, channelId: "C456" })).toBe(false);
+    expect(hasSlackThreadFailureNotice({ ...channelNotice, accountId: "A2" })).toBe(false);
+    expect(hasSlackThreadFailureNotice({ ...channelNotice, teamId: "T2" })).toBe(false);
+    expect(hasSlackThreadFailureNotice({ ...channelNotice, threadTs: "1700000000.000001" })).toBe(
+      false,
+    );
+
+    clearSlackThreadFailureNotice(channelNotice);
+    expect(hasSlackThreadFailureNotice(channelNotice)).toBe(false);
+    expect(recordSlackThreadFailureNotice(channelNotice)).toBe(true);
+  });
+
+  it("does not deduplicate failures with empty text", () => {
+    const notice = {
+      accountId: "A1",
+      channelId: "C123",
+      failureText: "   ",
+    };
+
+    expect(hasSlackThreadFailureNotice(notice)).toBe(false);
+    expect(recordSlackThreadFailureNotice(notice)).toBe(false);
+  });
+
+  it("isolates thread failures by account, channel, thread, and enterprise workspace", () => {
+    const notice = {
+      accountId: "A1",
+      channelId: "C123",
+      threadTs: "1700000000.000001",
+      failureText: "Model login expired",
+      teamId: "T1",
+    };
+
+    expect(recordSlackThreadFailureNotice(notice)).toBe(true);
+    expect(recordSlackThreadFailureNotice({ ...notice, accountId: "A2" })).toBe(true);
+    expect(recordSlackThreadFailureNotice({ ...notice, channelId: "C456" })).toBe(true);
+    expect(recordSlackThreadFailureNotice({ ...notice, threadTs: "1700000000.000002" })).toBe(true);
+    expect(recordSlackThreadFailureNotice({ ...notice, teamId: "T2" })).toBe(true);
+    expect(recordSlackThreadFailureNotice(notice)).toBe(false);
+  });
+
+  it("allows the same thread failure again after a successful turn clears its notice", () => {
+    const notice = {
+      accountId: "A1",
+      channelId: "C123",
+      threadTs: "1700000000.000001",
+      failureText: "Model login expired",
+    };
+
+    expect(recordSlackThreadFailureNotice(notice)).toBe(true);
+    clearSlackThreadFailureNotice(notice);
+    expect(recordSlackThreadFailureNotice(notice)).toBe(true);
+  });
+
+  it("does not treat failure notices as thread participation", () => {
+    recordSlackThreadFailureNotice({
+      accountId: "A1",
+      channelId: "C123",
+      threadTs: "1700000000.000001",
+      failureText: "Model login expired",
+    });
+
+    expect(hasSlackThreadParticipation("A1", "C123", "1700000000.000001")).toBe(false);
+  });
+
+  it("bounds failure notices and evicts the oldest thread", () => {
+    const firstNotice = {
+      accountId: "A1",
+      channelId: "C123",
+      threadTs: "1700000000.000000",
+      failureText: "Model login expired",
+    };
+    expect(recordSlackThreadFailureNotice(firstNotice)).toBe(true);
+
+    for (let index = 1; index <= 1000; index += 1) {
+      expect(
+        recordSlackThreadFailureNotice({
+          ...firstNotice,
+          threadTs: `1700000000.${String(index).padStart(6, "0")}`,
+        }),
+      ).toBe(true);
+    }
+
+    expect(recordSlackThreadFailureNotice(firstNotice)).toBe(true);
+  });
+
   it("ignores empty accountId, channelId, or threadTs", () => {
     recordSlackThreadParticipation("", "C123", "1700000000.000001");
     recordSlackThreadParticipation("A1", "", "1700000000.000001");
@@ -84,9 +223,18 @@ describe("slack sent-thread-cache", () => {
     try {
       cacheA.recordSlackThreadParticipation("A1", "C123", "1700000000.000001");
       expect(cacheB.hasSlackThreadParticipation("A1", "C123", "1700000000.000001")).toBe(true);
+      const failureNotice = {
+        accountId: "A1",
+        channelId: "C123",
+        threadTs: "1700000000.000001",
+        failureText: "Model login expired",
+      };
+      expect(cacheA.recordSlackThreadFailureNotice(failureNotice)).toBe(true);
+      expect(cacheB.recordSlackThreadFailureNotice(failureNotice)).toBe(false);
 
       cacheB.clearSlackThreadParticipationCache();
       expect(cacheA.hasSlackThreadParticipation("A1", "C123", "1700000000.000001")).toBe(false);
+      expect(cacheA.recordSlackThreadFailureNotice(failureNotice)).toBe(true);
     } finally {
       cacheA.clearSlackThreadParticipationCache();
     }
diff --git a/extensions/slack/src/sent-thread-cache.ts b/extensions/slack/src/sent-thread-cache.ts
index 96da39293459..90fb07eb539d 100644
--- a/extensions/slack/src/sent-thread-cache.ts
+++ b/extensions/slack/src/sent-thread-cache.ts
@@ -1,5 +1,6 @@
 // Slack plugin module implements sent thread cache behavior.
 import { createPersistentDedupeCache } from "openclaw/plugin-sdk/dedupe-runtime";
+import { resolveGlobalSingleton } from "openclaw/plugin-sdk/global-singleton";
 import { createPluginStateErrorReporter } from "openclaw/plugin-sdk/plugin-state-runtime";
 import { getOptionalSlackRuntime } from "./runtime.js";
 
@@ -10,6 +11,7 @@ import { getOptionalSlackRuntime } from "./runtime.js";
 
 const MAX_ENTRIES = 5000;
 const PERSISTENT_MAX_ENTRIES = 1000;
+const MAX_FAILURE_NOTICES = 1000;
 const PERSISTENT_NAMESPACE = "slack.thread-participation";
 
 type SlackThreadParticipationRecord = {
@@ -22,6 +24,7 @@ type SlackThreadParticipationRecord = {
  * auto-reply gating does not diverge between prepare/dispatch call paths.
  */
 const SLACK_THREAD_PARTICIPATION_KEY = Symbol.for("openclaw.slackThreadParticipation");
+const SLACK_THREAD_FAILURE_NOTICES_KEY = Symbol.for("openclaw.slackThreadFailureNotices");
 const threadParticipation = createPersistentDedupeCache<SlackThreadParticipationRecord>({
   globalKey: SLACK_THREAD_PARTICIPATION_KEY,
   // Participation remains valid until bounded oldest-entry eviction removes it.
@@ -39,6 +42,11 @@ const threadParticipation = createPersistentDedupeCache<SlackThreadParticipation
     ),
   },
 });
+const threadFailureNotices = resolveGlobalSingleton(
+  SLACK_THREAD_FAILURE_NOTICES_KEY,
+  () => new Map<string, string>(),
+  (notices) => notices.clear(),
+);
 
 function makeKey(accountId: string, channelId: string, threadTs: string, teamId?: string): string {
   return `${accountId}:${teamId ? `${teamId}:` : ""}${channelId}:${threadTs}`;
@@ -86,6 +94,66 @@ export async function hasSlackThreadParticipationWithPersistence(params: {
   );
 }
 
+type SlackFailureNotice = {
+  accountId: string;
+  channelId: string;
+  threadTs?: string;
+  failureText: string;
+  teamId?: string;
+};
+
+function makeFailureNoticeKey(params: Omit<SlackFailureNotice, "failureText">): string {
+  const scope = params.threadTs ? `thread:${params.threadTs}` : "channel";
+  return makeKey(params.accountId, params.channelId, scope, params.teamId);
+}
+
+/** Returns whether this failure was already delivered in the thread or channel. */
+export function hasSlackThreadFailureNotice(params: SlackFailureNotice): boolean {
+  const { accountId, channelId, failureText } = params;
+  const fingerprint = failureText.trim().replace(/\s+/gu, " ");
+  if (!accountId || !channelId || !fingerprint) {
+    return false;
+  }
+  return threadFailureNotices.get(makeFailureNoticeKey(params)) === fingerprint;
+}
+
+/** Records a failure after it was delivered in the thread or channel. */
+export function recordSlackThreadFailureNotice(params: SlackFailureNotice): boolean {
+  const { accountId, channelId, failureText } = params;
+  const fingerprint = failureText.trim().replace(/\s+/gu, " ");
+  if (!accountId || !channelId || !fingerprint) {
+    return false;
+  }
+  const key = makeFailureNoticeKey(params);
+  if (threadFailureNotices.get(key) === fingerprint) {
+    return false;
+  }
+  threadFailureNotices.delete(key);
+  threadFailureNotices.set(key, fingerprint);
+  if (threadFailureNotices.size > MAX_FAILURE_NOTICES) {
+    const oldestKey = threadFailureNotices.keys().next().value;
+    if (oldestKey !== undefined) {
+      threadFailureNotices.delete(oldestKey);
+    }
+  }
+  return true;
+}
+
+/** Clears a thread or channel outage notice after a healthy model turn completes. */
+export function clearSlackThreadFailureNotice(params: {
+  accountId: string;
+  channelId: string;
+  threadTs?: string;
+  teamId?: string;
+}): void {
+  const { accountId, channelId } = params;
+  if (!accountId || !channelId) {
+    return;
+  }
+  threadFailureNotices.delete(makeFailureNoticeKey(params));
+}
+
 export function clearSlackThreadParticipationCache(): void {
   threadParticipation.clearForTest();
+  threadFailureNotices.clear();
 }