test(workflow-utils): add error path tests for createLlmAdapter

Cover non-ok HTTP response (500) and network failure (ECONNREFUSED).
Per review feedback from 星月 🌙 on PR #278.

packages/workflow-utils/src/__tests__/create-llm-adapter.test.ts

@@ -51,4 +51,28 @@ describe("createLlmAdapter", () => {
       { role: "user", content: "trigger text" },
     ]);
   });
+
+  it("throws on non-ok fetch response", async () => {
+    const fetchMock = vi.fn().mockResolvedValue({
+      ok: false,
+      status: 500,
+      text: async () => "Internal Server Error",
+    });
+    vi.stubGlobal("fetch", fetchMock);
+
+    const provider = { baseUrl: "https://api.example/v1", apiKey: "k", model: "m" };
+    const adapter = createLlmAdapter(provider);
+
+    await expect(adapter(makeCtx("t1", "hi"), "sys")).rejects.toThrow("llm:");
+  });
+
+  it("throws on fetch network failure", async () => {
+    const fetchMock = vi.fn().mockRejectedValue(new Error("ECONNREFUSED"));
+    vi.stubGlobal("fetch", fetchMock);
+
+    const provider = { baseUrl: "https://api.example/v1", apiKey: "k", model: "m" };
+    const adapter = createLlmAdapter(provider);
+
+    await expect(adapter(makeCtx("t1", "hi"), "sys")).rejects.toThrow();
+  });
 });