diff --git a/extensions/whatsapp/src/auto-reply/monitor/echo.test.ts b/extensions/whatsapp/src/auto-reply/monitor/echo.test.ts
new file mode 100644
index 000000000000..2d2372fa1635
--- /dev/null
+++ b/extensions/whatsapp/src/auto-reply/monitor/echo.test.ts
@@ -0,0 +1,18 @@
+import { describe, expect, it, vi } from "vitest";
+import { createEchoTracker } from "./echo.js";
+
+describe("createEchoTracker", () => {
+  it("keeps verbose previews UTF-16 safe without changing the tracked text", () => {
+    const logVerbose = vi.fn();
+    const tracker = createEchoTracker({ logVerbose });
+    const prefix = "x".repeat(49);
+    const text = `${prefix}😀tail`;
+
+    tracker.rememberText(text, { logVerboseMessage: true });
+
+    expect(logVerbose).toHaveBeenCalledExactlyOnceWith(
+      `Added to echo detection set (size now: 1): ${prefix}...`,
+    );
+    expect(tracker.has(text)).toBe(true);
+  });
+});
diff --git a/extensions/whatsapp/src/auto-reply/monitor/echo.ts b/extensions/whatsapp/src/auto-reply/monitor/echo.ts
index 9d09f55b1302..b586b7330c02 100644
--- a/extensions/whatsapp/src/auto-reply/monitor/echo.ts
+++ b/extensions/whatsapp/src/auto-reply/monitor/echo.ts
@@ -1,4 +1,5 @@
 // Whatsapp plugin module implements echo behavior.
+import { truncateUtf16Safe } from "openclaw/plugin-sdk/text-utility-runtime";
 export type EchoTracker = {
   rememberText: (
     text: string | undefined,
@@ -48,7 +49,7 @@ export function createEchoTracker(params: {
     }
     if (opts.logVerboseMessage) {
       params.logVerbose?.(
-        `Added to echo detection set (size now: ${recentlySent.size}): ${text.slice(0, 50)}...`,
+        `Added to echo detection set (size now: ${recentlySent.size}): ${truncateUtf16Safe(text, 50)}...`,
       );
     }
     trim();