tests: document config mock choice for eager warmup

src/agents/context.eager-warmup.test.ts

@@ -2,6 +2,7 @@ import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
 
 const loadConfigMock = vi.hoisted(() => vi.fn());
 
+// context.js and command-auth.js still read other config exports at import time, so this test only stubs loadConfig while keeping the rest of the module real.
 vi.mock("../config/config.js", async (importOriginal) => {
   const actual = await importOriginal<typeof import("../config/config.js")>();
   return {