diff --git a/CHANGELOG.md b/CHANGELOG.md
index 47fda0a2858..cc32ac16cd4 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -256,6 +256,7 @@ Docs: https://docs.openclaw.ai
 - Synology Chat/reply delivery: resolve webhook usernames to Chat API `user_id` values for outbound chatbot replies, avoiding mismatches between webhook user IDs and `method=chatbot` recipient IDs in multi-account setups. (#23709) Thanks @druide67.
 - Slack/thread context payloads: only inject thread starter/history text on first thread turn for new sessions while preserving thread metadata, reducing repeated context-token bloat on long-lived thread sessions. (#32133) Thanks @sourman.
 - Slack/session routing: keep top-level channel messages in one shared session when `replyToMode=off`, while preserving thread-scoped keys for true thread replies and non-off modes. (#32193) Thanks @bmendonca3.
+- Slack/app_mention dedupe race handling: keep seen-message dedupe to prevent duplicate replies while allowing a one-time app_mention retry when the paired message event was dropped pre-dispatch, so requireMention channels do not lose mentions under Slack event reordering. (#34937) Thanks @littleben.
 - Voice-call/webhook routing: require exact webhook path matches (instead of prefix matches) so lookalike paths cannot reach provider verification/dispatch logic. (#31930) Thanks @afurm.
 - Zalo/Pairing auth tests: add webhook regression coverage asserting DM pairing-store reads/writes remain account-scoped, preventing cross-account authorization bleed in multi-account setups. (#26121) Thanks @bmendonca3.
 - Zalouser/Pairing auth tests: add account-scoped DM pairing-store regression coverage (`monitor.account-scope.test.ts`) to prevent cross-account allowlist bleed in multi-account setups. (#26672) Thanks @bmendonca3.
diff --git a/src/slack/monitor/message-handler.app-mention-race.test.ts b/src/slack/monitor/message-handler.app-mention-race.test.ts
new file mode 100644
index 00000000000..cfb44c8496e
--- /dev/null
+++ b/src/slack/monitor/message-handler.app-mention-race.test.ts
@@ -0,0 +1,157 @@
+import { beforeEach, describe, expect, it, vi } from "vitest";
+
+const prepareSlackMessageMock =
+  vi.fn<
+    (params: {
+      opts: { source: "message" | "app_mention"; wasMentioned?: boolean };
+    }) => Promise<unknown>
+  >();
+const dispatchPreparedSlackMessageMock = vi.fn<(prepared: unknown) => Promise<void>>();
+
+vi.mock("../../channels/inbound-debounce-policy.js", () => ({
+  shouldDebounceTextInbound: () => false,
+  createChannelInboundDebouncer: (params: {
+    onFlush: (
+      entries: Array<{
+        message: Record<string, unknown>;
+        opts: { source: "message" | "app_mention"; wasMentioned?: boolean };
+      }>,
+    ) => Promise<void>;
+  }) => ({
+    debounceMs: 0,
+    debouncer: {
+      enqueue: async (entry: {
+        message: Record<string, unknown>;
+        opts: { source: "message" | "app_mention"; wasMentioned?: boolean };
+      }) => {
+        await params.onFlush([entry]);
+      },
+      flushKey: async (_key: string) => {},
+    },
+  }),
+}));
+
+vi.mock("./thread-resolution.js", () => ({
+  createSlackThreadTsResolver: () => ({
+    resolve: async ({ message }: { message: Record<string, unknown> }) => message,
+  }),
+}));
+
+vi.mock("./message-handler/prepare.js", () => ({
+  prepareSlackMessage: (
+    params: Parameters<typeof prepareSlackMessageMock>[0],
+  ): ReturnType<typeof prepareSlackMessageMock> => prepareSlackMessageMock(params),
+}));
+
+vi.mock("./message-handler/dispatch.js", () => ({
+  dispatchPreparedSlackMessage: (
+    prepared: Parameters<typeof dispatchPreparedSlackMessageMock>[0],
+  ): ReturnType<typeof dispatchPreparedSlackMessageMock> =>
+    dispatchPreparedSlackMessageMock(prepared),
+}));
+
+import { createSlackMessageHandler } from "./message-handler.js";
+
+function createMarkMessageSeen() {
+  const seen = new Set<string>();
+  return (channel: string | undefined, ts: string | undefined) => {
+    if (!channel || !ts) {
+      return false;
+    }
+    const key = `${channel}:${ts}`;
+    if (seen.has(key)) {
+      return true;
+    }
+    seen.add(key);
+    return false;
+  };
+}
+
+describe("createSlackMessageHandler app_mention race handling", () => {
+  beforeEach(() => {
+    prepareSlackMessageMock.mockReset();
+    dispatchPreparedSlackMessageMock.mockReset();
+  });
+
+  it("allows a single app_mention retry when message event was dropped before dispatch", async () => {
+    prepareSlackMessageMock.mockImplementation(async ({ opts }) => {
+      if (opts.source === "message") {
+        return null;
+      }
+      return { ctxPayload: {} };
+    });
+
+    const handler = createSlackMessageHandler({
+      ctx: {
+        cfg: {},
+        accountId: "default",
+        app: { client: {} },
+        runtime: {},
+        markMessageSeen: createMarkMessageSeen(),
+      } as Parameters<typeof createSlackMessageHandler>[0]["ctx"],
+      account: { accountId: "default" } as Parameters<
+        typeof createSlackMessageHandler
+      >[0]["account"],
+    });
+
+    await handler(
+      { type: "message", channel: "C1", ts: "1700000000.000100", text: "hello" } as never,
+      { source: "message" },
+    );
+    await handler(
+      {
+        type: "app_mention",
+        channel: "C1",
+        ts: "1700000000.000100",
+        text: "<@U_BOT> hello",
+      } as never,
+      { source: "app_mention", wasMentioned: true },
+    );
+    await handler(
+      {
+        type: "app_mention",
+        channel: "C1",
+        ts: "1700000000.000100",
+        text: "<@U_BOT> hello",
+      } as never,
+      { source: "app_mention", wasMentioned: true },
+    );
+
+    expect(prepareSlackMessageMock).toHaveBeenCalledTimes(2);
+    expect(dispatchPreparedSlackMessageMock).toHaveBeenCalledTimes(1);
+  });
+
+  it("keeps app_mention deduped when message event already dispatched", async () => {
+    prepareSlackMessageMock.mockResolvedValue({ ctxPayload: {} });
+
+    const handler = createSlackMessageHandler({
+      ctx: {
+        cfg: {},
+        accountId: "default",
+        app: { client: {} },
+        runtime: {},
+        markMessageSeen: createMarkMessageSeen(),
+      } as Parameters<typeof createSlackMessageHandler>[0]["ctx"],
+      account: { accountId: "default" } as Parameters<
+        typeof createSlackMessageHandler
+      >[0]["account"],
+    });
+
+    await handler(
+      { type: "message", channel: "C1", ts: "1700000000.000200", text: "hello" } as never,
+      { source: "message" },
+    );
+    await handler(
+      {
+        type: "app_mention",
+        channel: "C1",
+        ts: "1700000000.000200",
+        text: "<@U_BOT> hello",
+      } as never,
+      { source: "app_mention", wasMentioned: true },
+    );
+
+    expect(prepareSlackMessageMock).toHaveBeenCalledTimes(1);
+    expect(dispatchPreparedSlackMessageMock).toHaveBeenCalledTimes(1);
+  });
+});
diff --git a/src/slack/monitor/message-handler.ts b/src/slack/monitor/message-handler.ts
index 647c9a62c53..7ad7d792bc1 100644
--- a/src/slack/monitor/message-handler.ts
+++ b/src/slack/monitor/message-handler.ts
@@ -15,6 +15,8 @@ export type SlackMessageHandler = (
   opts: { source: "message" | "app_mention"; wasMentioned?: boolean },
 ) => Promise<void>;
 
+const APP_MENTION_RETRY_TTL_MS = 60_000;
+
 function resolveSlackSenderId(message: SlackMessageEvent): string | null {
   return message.user ?? message.bot_id ?? null;
 }
@@ -51,6 +53,13 @@ function shouldDebounceSlackMessage(message: SlackMessageEvent, cfg: SlackMonito
   });
 }
 
+function buildSeenMessageKey(channelId: string | undefined, ts: string | undefined): string | null {
+  if (!channelId || !ts) {
+    return null;
+  }
+  return `${channelId}:${ts}`;
+}
+
 /**
  * Build a debounce key that isolates messages by thread (or by message timestamp
  * for top-level non-DM channel messages). Without per-message scoping, concurrent
@@ -133,9 +142,18 @@ export function createSlackMessageHandler(params: {
           wasMentioned: combinedMentioned || last.opts.wasMentioned,
         },
       });
+      const seenMessageKey = buildSeenMessageKey(last.message.channel, last.message.ts);
       if (!prepared) {
+        const hasMessageSource = entries.some((entry) => entry.opts.source === "message");
+        const hasAppMentionSource = entries.some((entry) => entry.opts.source === "app_mention");
+        if (seenMessageKey && hasMessageSource && !hasAppMentionSource) {
+          rememberAppMentionRetryKey(seenMessageKey);
+        }
         return;
       }
+      if (seenMessageKey) {
+        appMentionRetryKeys.delete(seenMessageKey);
+      }
       if (entries.length > 1) {
         const ids = entries.map((entry) => entry.message.ts).filter(Boolean) as string[];
         if (ids.length > 0) {
@@ -152,6 +170,31 @@ export function createSlackMessageHandler(params: {
   });
   const threadTsResolver = createSlackThreadTsResolver({ client: ctx.app.client });
   const pendingTopLevelDebounceKeys = new Map<string, Set<string>>();
+  const appMentionRetryKeys = new Map<string, number>();
+
+  const pruneAppMentionRetryKeys = (now: number) => {
+    for (const [key, expiresAt] of appMentionRetryKeys) {
+      if (expiresAt <= now) {
+        appMentionRetryKeys.delete(key);
+      }
+    }
+  };
+
+  const rememberAppMentionRetryKey = (key: string) => {
+    const now = Date.now();
+    pruneAppMentionRetryKeys(now);
+    appMentionRetryKeys.set(key, now + APP_MENTION_RETRY_TTL_MS);
+  };
+
+  const consumeAppMentionRetryKey = (key: string) => {
+    const now = Date.now();
+    pruneAppMentionRetryKeys(now);
+    if (!appMentionRetryKeys.has(key)) {
+      return false;
+    }
+    appMentionRetryKeys.delete(key);
+    return true;
+  };
 
   return async (message, opts) => {
     if (opts.source === "message" && message.type !== "message") {
@@ -165,8 +208,13 @@ export function createSlackMessageHandler(params: {
     ) {
       return;
     }
-    if (ctx.markMessageSeen(message.channel, message.ts)) {
-      return;
+    const seenMessageKey = buildSeenMessageKey(message.channel, message.ts);
+    if (seenMessageKey && ctx.markMessageSeen(message.channel, message.ts)) {
+      // Allow exactly one app_mention retry if the same ts was previously dropped
+      // from the message stream before it reached dispatch.
+      if (opts.source !== "app_mention" || !consumeAppMentionRetryKey(seenMessageKey)) {
+        return;
+      }
     }
     trackEvent?.();
     const resolvedMessage = await threadTsResolver.resolve({ message, source: opts.source });