Add test to ensure that default model exists

Author: ishulgin

src/__tests__/CodexACPAgent/e2e/acp-e2e-models-availability.test.ts

@@ -0,0 +1,23 @@
+import {afterEach, beforeEach, expect, it} from "vitest";
+import {createAuthenticatedFixture, describeE2E, type SpawnedAgentFixture,} from "./acp-e2e-test-utils";
+import {ModelId} from "../../../ModelId";
+
+const DEFAULT_MODEL_ID = ModelId.create("gpt-5.4-mini", "medium")
+
+describeE2E("Models availability", () => {
+    let fixture: SpawnedAgentFixture;
+
+    beforeEach(async () => {
+        fixture = await createAuthenticatedFixture();
+    });
+
+    afterEach(async () => {
+        await fixture.dispose();
+    });
+
+    it(`default model is available`, async () => {
+        const session = await fixture.createSession();
+        const models = session.models?.availableModels?.map(m => m.modelId);
+        expect(models).toContain(DEFAULT_MODEL_ID.toString())
+    });
+});