diff --git a/src/server/live.ts b/src/server/live.ts
index c430e0fdb..da81a0f0b 100644
--- a/src/server/live.ts
+++ b/src/server/live.ts
@@ -80,20 +80,10 @@ export const LIVE_CLIENT_PROTOCOL_HEADERS = [
  *
  * When `OCX_LIVE_FRAME_LOG` is set to a file path, every relayed sideband frame appends one
  * JSONL record: direction, frame kind, byte length, and whether the payload contains U+FFFD.
- * Privacy: full frame payloads are never written — only when U+FFFD is present, a short
- * excerpt around the first replacement character is included so the corruption point can be
- * attributed (upstream vs relay vs client). Disabled entirely when the env var is unset.
+ * Privacy: frame payloads are never written. The log is created with owner-only permissions and
+ * is disabled entirely when the env var is unset.
  */
 export const LIVE_FRAME_LOG_ENV = "OCX_LIVE_FRAME_LOG";
-const LIVE_FRAME_LOG_CONTEXT_CHARS = 24;
-
-function fffdContext(text: string): string | undefined {
-  const idx = text.indexOf("\uFFFD");
-  if (idx < 0) return undefined;
-  const start = Math.max(0, idx - LIVE_FRAME_LOG_CONTEXT_CHARS);
-  const end = Math.min(text.length, idx + LIVE_FRAME_LOG_CONTEXT_CHARS);
-  return text.slice(start, end);
-}
 
 export function logLiveSidebandFrame(dir: "c2u" | "u2c", data: unknown): void {
   const logPath = process.env[LIVE_FRAME_LOG_ENV];
@@ -101,18 +91,18 @@ export function logLiveSidebandFrame(dir: "c2u" | "u2c", data: unknown): void {
   try {
     let kind: "text" | "binary" = "binary";
     let bytes = 0;
-    let context: string | undefined;
+    let fffd = false;
     if (typeof data === "string") {
       kind = "text";
       bytes = Buffer.byteLength(data);
-      context = fffdContext(data);
+      fffd = data.includes("\uFFFD");
     } else if (data instanceof ArrayBuffer) {
       bytes = data.byteLength;
-      context = fffdContext(new TextDecoder().decode(new Uint8Array(data)));
+      fffd = new TextDecoder().decode(new Uint8Array(data)).includes("\uFFFD");
     } else if (ArrayBuffer.isView(data)) {
       const view = new Uint8Array(data.buffer, data.byteOffset, data.byteLength);
       bytes = data.byteLength;
-      context = fffdContext(new TextDecoder().decode(view));
+      fffd = new TextDecoder().decode(view).includes("\uFFFD");
     } else {
       return;
     }
@@ -121,10 +111,9 @@ export function logLiveSidebandFrame(dir: "c2u" | "u2c", data: unknown): void {
       dir,
       kind,
       bytes,
-      fffd: context !== undefined,
-      ...(context !== undefined ? { context } : {}),
+      fffd,
     };
-    appendFileSync(logPath, `${JSON.stringify(record)}\n`);
+    appendFileSync(logPath, `${JSON.stringify(record)}\n`, { mode: 0o600 });
   } catch {
     // Frame forensics must never break the relay.
   }
diff --git a/tests/server-live.test.ts b/tests/server-live.test.ts
index 8197527fb..ca83e2167 100644
--- a/tests/server-live.test.ts
+++ b/tests/server-live.test.ts
@@ -3,7 +3,7 @@
  * so the proxy must relay it to an OpenAI upstream instead of the /v1/* JSON-404 guard.
  */
 import { afterEach, beforeEach, describe, expect, test } from "bun:test";
-import { existsSync, mkdirSync, readFileSync, rmSync } from "node:fs";
+import { existsSync, mkdirSync, readFileSync, rmSync, statSync } from "node:fs";
 import { join } from "node:path";
 import { saveCodexAccountCredential } from "../src/codex/account-store";
 import { clearAccountNeedsReauth, clearAccountQuota } from "../src/codex/auth-api";
@@ -760,7 +760,7 @@ test("sideband relay preserves multibyte UTF-8 frames byte-identically in both d
 // The env-gated frame forensic log (OCX_LIVE_FRAME_LOG) records per-frame metadata and
 // U+FFFD presence without writing full payloads — the attribution tool for multibyte
 // transcript corruption reports.
-test("sideband frame log records direction, kind, and U+FFFD context without full payloads", async () => {
+test("sideband frame log records metadata without payload content", async () => {
   const frameLogPath = join(TEST_DIR, "frames.jsonl");
   process.env.OCX_LIVE_FRAME_LOG = frameLogPath;
   const FFFD_TEXT = "가볍게 ��기핼봐요";
@@ -839,13 +839,15 @@ test("sideband frame log records direction, kind, and U+FFFD context without ful
     expect(u2cFffd).toBeDefined();
     expect(u2cFffd.kind).toBe("text");
     expect(u2cFffd.bytes).toBeGreaterThan(0);
-    expect(u2cFffd.context).toContain("�");
+    expect(u2cFffd).not.toHaveProperty("context");
     expect(c2uClean).toBeDefined();
     expect(c2uClean.fffd).toBe(false);
-    // Full payloads must never be logged — only short FFFD context excerpts.
+    // No payload content is logged, including frames containing U+FFFD.
     for (const line of lines) {
       expect(JSON.stringify(line)).not.toContain("clean-frame");
+      expect(JSON.stringify(line)).not.toContain(FFFD_TEXT);
     }
+    if (process.platform !== "win32") expect(statSync(frameLogPath).mode & 0o777).toBe(0o600);
 
     client.close();
   } finally {