From 34f50b4860c8ea1773cdfb607d15a90b346f8b6e Mon Sep 17 00:00:00 2001
From: Dallin Romney <dallinromney@gmail.com>
Date: Thu, 20 Aug 2026 22:35:44 -0700
Subject: [PATCH] fix(codex): preserve omitted resume effort

---
 .../src/app-server/thread-lifecycle-io.ts     |  4 ++-
 .../thread-lifecycle.binding.test.ts          | 34 +++++++++++++++++++
 2 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/extensions/codex/src/app-server/thread-lifecycle-io.ts b/extensions/codex/src/app-server/thread-lifecycle-io.ts
index 6540aee8724e..1f96c9331b9b 100644
--- a/extensions/codex/src/app-server/thread-lifecycle-io.ts
+++ b/extensions/codex/src/app-server/thread-lifecycle-io.ts
@@ -285,7 +285,9 @@ export async function resumeExistingCodexThread(
         boundAuthProfileId,
         response.modelProvider ?? requestModelProvider ?? startModelProvider,
       ),
-      reasoningEffort: response.reasoningEffort,
+      ...(response.reasoningEffort !== undefined
+        ? { reasoningEffort: response.reasoningEffort }
+        : {}),
       dynamicToolsFingerprint,
       dynamicToolsContainDeferred,
       webSearchThreadConfigFingerprint,
diff --git a/extensions/codex/src/app-server/thread-lifecycle.binding.test.ts b/extensions/codex/src/app-server/thread-lifecycle.binding.test.ts
index abe6838dcbb2..0faf83beeae2 100644
--- a/extensions/codex/src/app-server/thread-lifecycle.binding.test.ts
+++ b/extensions/codex/src/app-server/thread-lifecycle.binding.test.ts
@@ -291,6 +291,40 @@ function createTwoCalendarAppPolicyContext() {
 setupRunAttemptTestHooks();
 
 describe("Codex app-server thread lifecycle bindings", () => {
+  it("preserves the stored reasoning effort when resume omits it", async () => {
+    const sessionFile = path.join(tempDir, "session-effort.jsonl");
+    const workspaceDir = path.join(tempDir, "workspace-effort");
+    const threadId = "thread-effort";
+    const request = vi.fn(async (method: string) => {
+      const response = threadStartResult(threadId);
+      if (method === "thread/start") {
+        return { ...response, reasoningEffort: "high" };
+      }
+      if (method === "thread/resume") {
+        const { reasoningEffort: _reasoningEffort, ...withoutReasoningEffort } = response;
+        return withoutReasoningEffort;
+      }
+      throw new Error(`unexpected method: ${method}`);
+    });
+    const common = {
+      client: { getInstanceId: () => "effort-client", request } as never,
+      params: createParams(sessionFile, workspaceDir),
+      cwd: workspaceDir,
+      dynamicTools: [],
+      appServer: createThreadLifecycleAppServerOptions(),
+      userMcpServersEnabled: false,
+    };
+
+    await startOrResumeThread(common);
+    await startOrResumeThread(common);
+
+    expect(request.mock.calls.map(([method]) => method)).toEqual(["thread/start", "thread/resume"]);
+    await expect(readCodexAppServerBinding(sessionFile)).resolves.toMatchObject({
+      threadId,
+      reasoningEffort: "high",
+    });
+  });
+
   it("persists the native rollout path across thread start and resume", async () => {
     const sessionFile = path.join(tempDir, "session.jsonl");
     const workspaceDir = path.join(tempDir, "workspace");