diff --git a/extensions/codex/index.test.ts b/extensions/codex/index.test.ts
index fe6d91495a3..c034fe28374 100644
--- a/extensions/codex/index.test.ts
+++ b/extensions/codex/index.test.ts
@@ -4,6 +4,14 @@ import { describe, expect, it, vi } from "vitest";
 import { createCodexAppServerAgentHarness } from "./harness.js";
 import plugin from "./index.js";
 
+function mockCall(mock: { mock: { calls: unknown[][] } }, index = 0) {
+  return mock.mock.calls.at(index);
+}
+
+function mockCallArg(mock: { mock: { calls: unknown[][] } }, index = 0, argIndex = 0) {
+  return mockCall(mock, index)?.at(argIndex);
+}
+
 describe("codex plugin", () => {
   it("is opt-in by default", () => {
     const manifest = JSON.parse(
@@ -40,16 +48,13 @@ describe("codex plugin", () => {
       }),
     );
 
-    const providerRegistration = registerProvider.mock.calls[0]?.[0] as Record<string, unknown>;
-    const agentHarnessRegistration = registerAgentHarness.mock.calls[0]?.[0] as Record<
-      string,
-      unknown
-    >;
-    const mediaProviderRegistration = registerMediaUnderstandingProvider.mock.calls[0]?.[0] as
+    const providerRegistration = mockCallArg(registerProvider) as Record<string, unknown>;
+    const agentHarnessRegistration = mockCallArg(registerAgentHarness) as Record<string, unknown>;
+    const mediaProviderRegistration = mockCallArg(registerMediaUnderstandingProvider) as
       | Record<string, unknown>
       | undefined;
-    const inboundClaimRegistration = on.mock.calls[0] as [unknown, unknown] | undefined;
-    const bindingResolvedRegistration = onConversationBindingResolved.mock.calls[0] as
+    const inboundClaimRegistration = mockCall(on) as [unknown, unknown] | undefined;
+    const bindingResolvedRegistration = mockCall(onConversationBindingResolved) as
       | [unknown]
       | undefined;
 
@@ -66,12 +71,14 @@ describe("codex plugin", () => {
     expect(mediaProviderRegistration?.defaultModels).toEqual({ image: "gpt-5.5" });
     expect(typeof mediaProviderRegistration?.describeImage).toBe("function");
     expect(typeof mediaProviderRegistration?.describeImages).toBe("function");
-    const commandRegistration = registerCommand.mock.calls[0]?.[0];
+    const commandRegistration = mockCallArg(registerCommand) as Record<string, unknown> | undefined;
     expect(commandRegistration?.name).toBe("codex");
     expect(commandRegistration?.description).toBe(
       "Inspect and control the Codex app-server harness",
     );
-    const migrationRegistration = registerMigrationProvider.mock.calls[0]?.[0];
+    const migrationRegistration = mockCallArg(registerMigrationProvider) as
+      | Record<string, unknown>
+      | undefined;
     expect(migrationRegistration?.id).toBe("codex");
     expect(migrationRegistration?.label).toBe("Codex");
     expect(inboundClaimRegistration?.[0]).toBe("inbound_claim");
@@ -98,7 +105,7 @@ describe("codex plugin", () => {
 
     plugin.register(api);
     expect(registerProvider).toHaveBeenCalledTimes(1);
-    expect(registerProvider.mock.calls[0]?.[0].id).toBe("codex");
+    expect((mockCallArg(registerProvider) as { id?: string } | undefined)?.id).toBe("codex");
   });
 
   it("only claims the codex provider by default", () => {