diff --git a/extensions/qa-lab/src/gateway-child.test.ts b/extensions/qa-lab/src/gateway-child.test.ts
index 7c2295ed0089..567c59475449 100644
--- a/extensions/qa-lab/src/gateway-child.test.ts
+++ b/extensions/qa-lab/src/gateway-child.test.ts
@@ -206,6 +206,18 @@ describe("formatQaGatewayProcessBoundaryStartupFailure", () => {
     expect(message).not.toContain("s".repeat(100));
     expect(message).not.toContain(prefix);
   });
+
+  it("preserves complete Unicode code points at the retained log-tail boundary", () => {
+    const message = testing.formatQaGatewayProcessBoundaryStartupFailure(
+      new Error("launcher exited before identity"),
+      `P😀${"z".repeat(8_191)}`,
+    );
+
+    expect(message).not.toMatch(
+      /[\uD800-\uDBFF](?![\uDC00-\uDFFF])|(?<![\uD800-\uDBFF])[\uDC00-\uDFFF]/u,
+    );
+    expect(Buffer.from(message, "utf8").toString("utf8")).not.toContain("�");
+  });
 });
 
 describe("Gateway child fixture helpers", () => {
diff --git a/extensions/qa-lab/src/gateway-child.ts b/extensions/qa-lab/src/gateway-child.ts
index edba1decf248..2f8c051ad354 100644
--- a/extensions/qa-lab/src/gateway-child.ts
+++ b/extensions/qa-lab/src/gateway-child.ts
@@ -18,6 +18,7 @@ import {
   uniqueStrings,
 } from "openclaw/plugin-sdk/string-coerce-runtime";
 import { resolvePreferredOpenClawTmpDir } from "openclaw/plugin-sdk/temp-path";
+import { sliceUtf16Safe } from "openclaw/plugin-sdk/text-utility-runtime";
 import {
   createQaBundledPluginsDir,
   resolveQaBundledPluginSourceDir,
@@ -493,7 +494,10 @@ function monitorQaGatewayChildFailure(child: ChildProcess, output: { push(chunk:
 const QA_GATEWAY_PROCESS_BOUNDARY_LOG_TAIL_CHARS = 8_192;
 
 function formatQaGatewayProcessBoundaryStartupFailure(error: unknown, logs: string) {
-  const logTail = redactQaGatewayDebugText(logs).slice(-QA_GATEWAY_PROCESS_BOUNDARY_LOG_TAIL_CHARS);
+  const logTail = sliceUtf16Safe(
+    redactQaGatewayDebugText(logs),
+    -QA_GATEWAY_PROCESS_BOUNDARY_LOG_TAIL_CHARS,
+  );
   return `${formatErrorMessage(error)}${formatQaGatewayLogsForError(logTail)}`;
 }