agents: add tests for engine router

Test engine router switching logic between embedded
and AI SDK engines.

src/agents/engine-router.test.ts

@@ -0,0 +1,44 @@
+import { describe, expect, it } from "vitest";
+import { getConfiguredEngine, getEngineInfo, DEFAULT_ENGINE } from "./engine-router.js";
+
+describe("Engine Router", () => {
+  describe("getConfiguredEngine", () => {
+    it("returns aisdk by default when no config", () => {
+      expect(getConfiguredEngine()).toBe("aisdk");
+    });
+
+    it("returns aisdk by default when config has no engine", () => {
+      expect(getConfiguredEngine({})).toBe("aisdk");
+      expect(getConfiguredEngine({ agents: {} })).toBe("aisdk");
+    });
+
+    it("returns pi-agent when configured", () => {
+      expect(getConfiguredEngine({ agents: { engine: "pi-agent" } })).toBe("pi-agent");
+    });
+
+    it("returns aisdk when explicitly configured", () => {
+      expect(getConfiguredEngine({ agents: { engine: "aisdk" } })).toBe("aisdk");
+    });
+  });
+
+  describe("getEngineInfo", () => {
+    it("returns current and default engine info", () => {
+      const info = getEngineInfo();
+      expect(info.current).toBe(DEFAULT_ENGINE);
+      expect(info.default).toBe("aisdk");
+      expect(info.configPath).toBe("agents.engine");
+    });
+
+    it("reflects configured engine", () => {
+      const info = getEngineInfo({ agents: { engine: "pi-agent" } });
+      expect(info.current).toBe("pi-agent");
+      expect(info.default).toBe("aisdk");
+    });
+  });
+
+  describe("DEFAULT_ENGINE", () => {
+    it("is aisdk", () => {
+      expect(DEFAULT_ENGINE).toBe("aisdk");
+    });
+  });
+});