diff --git a/extensions/codex/src/app-server/client.test.ts b/extensions/codex/src/app-server/client.test.ts
index 8f30b5da360..b2545f64eb1 100644
--- a/extensions/codex/src/app-server/client.test.ts
+++ b/extensions/codex/src/app-server/client.test.ts
@@ -1,5 +1,5 @@
 import { EventEmitter } from "node:events";
-import { PassThrough, Writable } from "node:stream";
+import { PassThrough } from "node:stream";
 import { afterEach, describe, expect, it, vi } from "vitest";
 import {
   __testing,
@@ -9,42 +9,23 @@ import {
   readCodexVersionFromUserAgent,
 } from "./client.js";
 import { resetSharedCodexAppServerClientForTests } from "./shared-client.js";
-
-function createClientHarness() {
-  const stdout = new PassThrough();
-  const stderr = new PassThrough();
-  const writes: string[] = [];
-  const stdin = new Writable({
-    write(chunk, _encoding, callback) {
-      writes.push(chunk.toString());
-      callback();
-    },
-  });
-  const process = Object.assign(new EventEmitter(), {
-    stdin,
-    stdout,
-    stderr,
-    killed: false,
-    kill: vi.fn(() => {
-      process.killed = true;
-    }),
-  });
-  // fromTransportForTests speaks the same newline-delimited JSON-RPC as the
-  // spawned app-server, but keeps the process lifecycle fully observable.
-  const client = CodexAppServerClient.fromTransportForTests(process);
-  return {
-    client,
-    process,
-    writes,
-    send(message: unknown) {
-      stdout.write(`${JSON.stringify(message)}\n`);
-    },
-  };
-}
+import { createClientHarness } from "./test-support.js";
 
 describe("CodexAppServerClient", () => {
   const clients: CodexAppServerClient[] = [];
 
+  function startInitialize() {
+    const harness = createClientHarness();
+    clients.push(harness.client);
+    const initializing = harness.client.initialize();
+    const outbound = JSON.parse(harness.writes[0] ?? "{}") as {
+      id?: number;
+      method?: string;
+      params?: { clientInfo?: { name?: string; title?: string; version?: string } };
+    };
+    return { harness, initializing, outbound };
+  }
+
   afterEach(() => {
     resetSharedCodexAppServerClientForTests();
     vi.useRealTimers();
@@ -115,15 +96,7 @@ describe("CodexAppServerClient", () => {
   });
 
   it("initializes with the required client version", async () => {
-    const harness = createClientHarness();
-    clients.push(harness.client);
-
-    const initializing = harness.client.initialize();
-    const outbound = JSON.parse(harness.writes[0] ?? "{}") as {
-      id?: number;
-      method?: string;
-      params?: { clientInfo?: { name?: string; title?: string; version?: string } };
-    };
+    const { harness, initializing, outbound } = startInitialize();
     harness.send({
       id: outbound.id,
       result: { userAgent: "openclaw/0.118.0 (macOS; test)" },
@@ -145,11 +118,7 @@ describe("CodexAppServerClient", () => {
   });
 
   it("blocks unsupported app-server versions during initialize", async () => {
-    const harness = createClientHarness();
-    clients.push(harness.client);
-
-    const initializing = harness.client.initialize();
-    const outbound = JSON.parse(harness.writes[0] ?? "{}") as { id?: number };
+    const { harness, initializing, outbound } = startInitialize();
     harness.send({
       id: outbound.id,
       result: { userAgent: "openclaw/0.117.9 (macOS; test)" },
@@ -162,11 +131,7 @@ describe("CodexAppServerClient", () => {
   });
 
   it("blocks app-server initialize responses without a version", async () => {
-    const harness = createClientHarness();
-    clients.push(harness.client);
-
-    const initializing = harness.client.initialize();
-    const outbound = JSON.parse(harness.writes[0] ?? "{}") as { id?: number };
+    const { harness, initializing, outbound } = startInitialize();
     harness.send({ id: outbound.id, result: {} });
 
     await expect(initializing).rejects.toThrow(
diff --git a/extensions/codex/src/app-server/transcript-mirror.test.ts b/extensions/codex/src/app-server/transcript-mirror.test.ts
index adaddf578d4..5574d1eca8c 100644
--- a/extensions/codex/src/app-server/transcript-mirror.test.ts
+++ b/extensions/codex/src/app-server/transcript-mirror.test.ts
@@ -1,11 +1,32 @@
 import fs from "node:fs/promises";
 import os from "node:os";
 import path from "node:path";
+import type { AgentMessage } from "@mariozechner/pi-agent-core";
 import { afterEach, beforeEach, describe, expect, it } from "vitest";
 import { mirrorCodexAppServerTranscript } from "./transcript-mirror.js";
 
 let tempDir: string;
 
+function assistantMessage(text: string, timestamp: number): AgentMessage {
+  return {
+    role: "assistant",
+    content: [{ type: "text", text }],
+    api: "openai-codex-responses",
+    provider: "openai-codex",
+    model: "gpt-5.4-codex",
+    usage: {
+      input: 0,
+      output: 0,
+      cacheRead: 0,
+      cacheWrite: 0,
+      totalTokens: 0,
+      cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0, total: 0 },
+    },
+    stopReason: "stop",
+    timestamp,
+  };
+}
+
 describe("mirrorCodexAppServerTranscript", () => {
   beforeEach(async () => {
     tempDir = await fs.mkdtemp(path.join(os.tmpdir(), "openclaw-codex-transcript-"));
@@ -23,40 +44,8 @@ describe("mirrorCodexAppServerTranscript", () => {
       sessionKey: "agent:main:session-1",
       messages: [
         { role: "user", content: "hello", timestamp: 1 },
-        {
-          role: "assistant",
-          content: [{ type: "text", text: "Codex plan:\ninspect" }],
-          api: "openai-codex-responses",
-          provider: "openai-codex",
-          model: "gpt-5.4-codex",
-          usage: {
-            input: 0,
-            output: 0,
-            cacheRead: 0,
-            cacheWrite: 0,
-            totalTokens: 0,
-            cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0, total: 0 },
-          },
-          stopReason: "stop",
-          timestamp: 2,
-        },
-        {
-          role: "assistant",
-          content: [{ type: "text", text: "hi" }],
-          api: "openai-codex-responses",
-          provider: "openai-codex",
-          model: "gpt-5.4-codex",
-          usage: {
-            input: 0,
-            output: 0,
-            cacheRead: 0,
-            cacheWrite: 0,
-            totalTokens: 0,
-            cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0, total: 0 },
-          },
-          stopReason: "stop",
-          timestamp: 3,
-        },
+        assistantMessage("Codex plan:\ninspect", 2),
+        assistantMessage("hi", 3),
       ],
     });
 
@@ -76,23 +65,7 @@ describe("mirrorCodexAppServerTranscript", () => {
     const sessionFile = path.join(tempDir, "session.jsonl");
     const messages = [
       { role: "user" as const, content: "hello", timestamp: 1 },
-      {
-        role: "assistant" as const,
-        content: [{ type: "text" as const, text: "hi" }],
-        api: "openai-codex-responses",
-        provider: "openai-codex",
-        model: "gpt-5.4-codex",
-        usage: {
-          input: 0,
-          output: 0,
-          cacheRead: 0,
-          cacheWrite: 0,
-          totalTokens: 0,
-          cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0, total: 0 },
-        },
-        stopReason: "stop" as const,
-        timestamp: 2,
-      },
+      assistantMessage("hi", 2),
     ];
 
     await mirrorCodexAppServerTranscript({