diff --git a/CHANGELOG.md b/CHANGELOG.md
index fc886cba7e1..eebc60af1dd 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -25,6 +25,7 @@ Docs: https://docs.openclaw.ai
 ### Fixes
 
 - Codex harness: route native `request_user_input` prompts back to the originating chat, preserve queued follow-up answers, and honor newer app-server command approval amendment decisions.
+- Codex harness/context-engine: redact context-engine assembly failures before logging, so fallback warnings do not serialize raw error objects. (#70809) Thanks @jalehman.
 - Codex harness/Windows: resolve npm-installed `codex.cmd` shims through PATHEXT before starting the native app-server, so `codex/*` models work without a manual `.exe` shim. Fixes #70913.
 - Slack/groups: classify MPIM group DMs as group chat context and suppress verbose tool/plan progress on Slack non-DM surfaces, so internal "Working…" traces no longer leak into rooms. Fixes #70912.
 - Agents/replay: stop OpenAI/Codex transcript replay from synthesizing missing tool results while still preserving synthetic repair on Anthropic, Gemini, and Bedrock transport-owned sessions. (#61556) Thanks @VictorJeon and @vincentkoc.
diff --git a/extensions/codex/src/app-server/run-attempt.context-engine.test.ts b/extensions/codex/src/app-server/run-attempt.context-engine.test.ts
index 9598f3d4ffc..7a7f3f7b324 100644
--- a/extensions/codex/src/app-server/run-attempt.context-engine.test.ts
+++ b/extensions/codex/src/app-server/run-attempt.context-engine.test.ts
@@ -4,6 +4,7 @@ import path from "node:path";
 import type { AgentMessage } from "@mariozechner/pi-agent-core";
 import { SessionManager } from "@mariozechner/pi-coding-agent";
 import type { EmbeddedRunAttemptParams } from "openclaw/plugin-sdk/agent-harness";
+import { embeddedAgentLog } from "openclaw/plugin-sdk/agent-harness-runtime";
 import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
 import type { ContextEngine } from "../../../../src/context-engine/types.js";
 import type { CodexServerNotification } from "./protocol.js";
@@ -365,6 +366,41 @@ describe("runCodexAppServerAttempt context-engine lifecycle", () => {
     );
   });
 
+  it("logs assemble failures as a formatted message instead of the raw error object", async () => {
+    const sessionFile = path.join(tempDir, "session.jsonl");
+    const workspaceDir = path.join(tempDir, "workspace");
+    const rawError = new Error("Authorization: Bearer sk-abcdefghijklmnopqrstuv");
+    const contextEngine = createContextEngine({
+      assemble: vi.fn(async () => {
+        throw rawError;
+      }),
+      bootstrap: undefined,
+    });
+    const warn = vi.spyOn(embeddedAgentLog, "warn").mockImplementation(() => undefined);
+    const harness = createStartedThreadHarness();
+    const params = createParams(sessionFile, workspaceDir);
+    params.contextEngine = contextEngine;
+
+    const run = runCodexAppServerAttempt(params);
+    await harness.waitForMethod("turn/start");
+    await harness.completeTurn();
+    await run;
+
+    expect(warn).toHaveBeenCalledWith(
+      "context engine assemble failed; using Codex baseline prompt",
+      {
+        error: expect.any(String),
+      },
+    );
+    const warning = warn.mock.calls.find(
+      ([message]) => message === "context engine assemble failed; using Codex baseline prompt",
+    );
+    expect(warning?.[1]).not.toEqual({ error: rawError });
+    expect(String((warning?.[1] as { error?: unknown } | undefined)?.error)).not.toContain(
+      "sk-abcdefghijklmnopqrstuv",
+    );
+  });
+
   it("falls back to ingestBatch and skips turn maintenance on prompt failure", async () => {
     const sessionFile = path.join(tempDir, "session.jsonl");
     const workspaceDir = path.join(tempDir, "workspace");
diff --git a/extensions/codex/src/app-server/run-attempt.ts b/extensions/codex/src/app-server/run-attempt.ts
index c795b939785..8164d17d0de 100644
--- a/extensions/codex/src/app-server/run-attempt.ts
+++ b/extensions/codex/src/app-server/run-attempt.ts
@@ -217,7 +217,7 @@ export async function runCodexAppServerAttempt(
       prePromptMessageCount = projection.prePromptMessageCount;
     } catch (assembleErr) {
       embeddedAgentLog.warn("context engine assemble failed; using Codex baseline prompt", {
-        error: assembleErr,
+        error: formatErrorMessage(assembleErr),
       });
     }
   }