test(memory): dedupe model-auth mock setup

src/test-utils/model-auth-mock.ts

@@ -0,0 +1,13 @@
+import { vi } from "vitest";
+
+export function createModelAuthMockModule() {
+  return {
+    resolveApiKeyForProvider: vi.fn(),
+    requireApiKey: (auth: { apiKey?: string; mode?: string }, provider: string) => {
+      if (auth?.apiKey) {
+        return auth.apiKey;
+      }
+      throw new Error(`No API key resolved for provider "${provider}" (auth mode: ${auth?.mode}).`);
+    },
+  };
+}