diff --git a/src/agents/subagent-announce.ts b/src/agents/subagent-announce.ts
index 4d454a04bb7..b966af0c5e6 100644
--- a/src/agents/subagent-announce.ts
+++ b/src/agents/subagent-announce.ts
@@ -1,4 +1,4 @@
-import crypto from "node:crypto";
+import path from "node:path";
 import { resolveQueueSettings } from "../auto-reply/reply/queue.js";
 import { loadConfig } from "../config/config.js";
 import {
@@ -113,6 +113,13 @@ async function sendAnnounce(item: AnnounceQueueItem) {
   const origin = item.origin;
   const threadId =
     origin?.threadId != null && origin.threadId !== "" ? String(origin.threadId) : undefined;
+  // Use a deterministic idempotency key derived from the session key and
+  // enqueue timestamp so the gateway dedup cache catches duplicates when
+  // the announce is delivered via both the announce queue drain *and* the
+  // gateway-level message queue (which re-queues the callGateway "agent"
+  // call if the main session is still busy).
+  // See: https://github.com/openclaw/openclaw/issues/17122
+  const idempotencyKey = `announce:${item.sessionKey}:${item.enqueuedAt}`;
   await callGateway({
     method: "agent",
     params: {
@@ -123,7 +130,7 @@ async function sendAnnounce(item: AnnounceQueueItem) {
       to: requesterIsSubagent ? undefined : origin?.to,
       threadId: requesterIsSubagent ? undefined : threadId,
       deliver: !requesterIsSubagent,
-      idempotencyKey: crypto.randomUUID(),
+      idempotencyKey,
     },
     timeoutMs: 15_000,
   });
@@ -565,6 +572,10 @@ export async function runSubagentAnnounceFlow(params: {
       const { entry } = loadRequesterSessionEntry(targetRequesterSessionKey);
       directOrigin = deliveryContextFromSession(entry);
     }
+    // Use a deterministic idempotency key so the gateway dedup cache
+    // catches duplicates if this announce is also queued by the gateway-
+    // level message queue while the main session is busy (#17122).
+    const directIdempotencyKey = `announce:${params.childSessionKey}:${params.childRunId}`;
     await callGateway({
       method: "agent",
       params: {
@@ -578,7 +589,7 @@ export async function runSubagentAnnounceFlow(params: {
           !requesterIsSubagent && directOrigin?.threadId != null && directOrigin.threadId !== ""
             ? String(directOrigin.threadId)
             : undefined,
-        idempotencyKey: crypto.randomUUID(),
+        idempotencyKey: directIdempotencyKey,
       },
       expectFinal: true,
       timeoutMs: 15_000,