test: cover unreachable Ollama service errors

- Verify network-level fetch failures propagate from the generation client
- Assert the original error type and message are preserved
- Restore the global fetch implementation after the test

src/ollama.test.ts

@@ -45,3 +45,20 @@ it("throws an error when Ollama returns a non-OK status", async () => {
     globalThis.fetch = originalFetch;
   }
 });
+
+it("propagates an error when Ollama is unreachable", async () => {
+  const originalFetch = globalThis.fetch;
+
+  globalThis.fetch = async () => {
+    throw new TypeError("fetch failed");
+  };
+
+  try {
+    await assert.rejects(generateResponse("Explain a REST API."), {
+      name: "TypeError",
+      message: "fetch failed",
+    });
+  } finally {
+    globalThis.fetch = originalFetch;
+  }
+});