diff --git a/extensions/codex/src/app-server/run-attempt.test.ts b/extensions/codex/src/app-server/run-attempt.test.ts
index 28ef39e93ff..f8afccf4371 100644
--- a/extensions/codex/src/app-server/run-attempt.test.ts
+++ b/extensions/codex/src/app-server/run-attempt.test.ts
@@ -81,6 +81,25 @@ function buildCodexRuntimePlan(params: EmbeddedRunAttemptParams, workspaceDir: s
   });
 }
 
+function createCodexRuntimePlanFixture(): NonNullable<EmbeddedRunAttemptParams["runtimePlan"]> {
+  return {
+    auth: {},
+    observability: {
+      resolvedRef: "codex/gpt-5.4-codex",
+      provider: "codex",
+      modelId: "gpt-5.4-codex",
+      harnessId: "codex",
+    },
+    prompt: {
+      resolveSystemPromptContribution: () => undefined,
+    },
+    tools: {
+      normalize: (tools: unknown[]) => tools,
+      logDiagnostics: () => undefined,
+    },
+  } as unknown as NonNullable<EmbeddedRunAttemptParams["runtimePlan"]>;
+}
+
 function threadStartResult(threadId = "thread-1") {
   return {
     thread: {
@@ -933,7 +952,8 @@ describe("runCodexAppServerAttempt", () => {
     sessionManager.appendMessage(assistantMessage("existing context", Date.now()));
     const harness = createStartedThreadHarness();
 
-    const params = createParamsWithRuntimePlan(sessionFile, workspaceDir);
+    const params = createParams(sessionFile, workspaceDir);
+    params.runtimePlan = createCodexRuntimePlanFixture();
     params.onAgentEvent = onRunAgentEvent;
     const run = runCodexAppServerAttempt(params);
     await harness.waitForMethod("turn/start");