diff --git a/scripts/e2e/lib/agent-turn-output.mjs b/scripts/e2e/lib/agent-turn-output.mjs
index 2c2bec0f1eb4..12838da9a470 100644
--- a/scripts/e2e/lib/agent-turn-output.mjs
+++ b/scripts/e2e/lib/agent-turn-output.mjs
@@ -67,6 +67,19 @@ function parseJson(text) {
   }
 }
 
+function isJsonObjectRecordStart(text, index) {
+  for (let cursor = index - 1; cursor >= 0; cursor -= 1) {
+    const char = text[cursor];
+    if (char === "\n" || char === "\r") {
+      return true;
+    }
+    if (char !== " " && char !== "\t") {
+      return false;
+    }
+  }
+  return true;
+}
+
 function parseJsonObjectsFromText(text) {
   const payloads = [];
   let start = -1;
@@ -77,7 +90,7 @@ function parseJsonObjectsFromText(text) {
   for (let index = 0; index < text.length; index += 1) {
     const char = text[index];
     if (start === -1) {
-      if (char === "{") {
+      if (char === "{" && isJsonObjectRecordStart(text, index)) {
         start = index;
         depth = 1;
         inString = false;
diff --git a/test/scripts/e2e-agent-turn-output.test.ts b/test/scripts/e2e-agent-turn-output.test.ts
index d014d962c780..de6263c714ad 100644
--- a/test/scripts/e2e-agent-turn-output.test.ts
+++ b/test/scripts/e2e-agent-turn-output.test.ts
@@ -80,6 +80,26 @@ describe("scripts/e2e/lib/agent-turn-output", () => {
     }
   });
 
+  it("does not accept reply-shaped JSON embedded in diagnostic lines", () => {
+    const dir = mkdtempSync(join(tmpdir(), "openclaw-e2e-agent-output-"));
+    try {
+      const outputPath = join(dir, "agent.log");
+      writeFileSync(
+        outputPath,
+        [
+          `echo ${JSON.stringify({ payloads: [{ text: "OPENCLAW_E2E_OK_DIAGNOSTIC" }] })}`,
+          JSON.stringify({ payloads: [{ text: "real reply without marker" }] }),
+        ].join("\n"),
+      );
+
+      expect(() =>
+        assertAgentReplyContainsMarker("OPENCLAW_E2E_OK_DIAGNOSTIC", outputPath),
+      ).toThrow(/agent reply payload did not contain marker/u);
+    } finally {
+      rmSync(dir, { recursive: true, force: true });
+    }
+  });
+
   it("does not accept markers that only appear in error payload text", () => {
     const dir = mkdtempSync(join(tmpdir(), "openclaw-e2e-agent-output-"));
     try {