diff --git a/hc_agent.py b/hc_agent.py
new file mode 100644
index 0000000000..ae34feba54
--- /dev/null
+++ b/hc_agent.py
@@ -0,0 +1,40 @@
+import io
+import os
+import uuid
+
+import requests
+
+
+def preview(payload):
+    return {"mode": "preview", "payload": payload}
+
+
+def apply(payload, request_fn=None):
+    if request_fn is None:
+        request_fn = requests.request
+    return request_fn("POST", "http://hc-agent/apply", json=payload)
+
+
+class RunStore:
+    def __init__(self, root):
+        self.root = root
+
+    def run_dir(self, run_id):
+        return os.path.join(self.root, "runs", run_id)
+
+    def write_report(self, run_id, content):
+        run_dir = self.run_dir(run_id)
+        os.makedirs(run_dir, exist_ok=True)
+        report_path = os.path.join(run_dir, "report.md")
+        with io.open(report_path, "w", encoding="utf-8") as handle:
+            handle.write(content)
+        return report_path
+
+
+def gateway_run(payload, runstore_root, run_id=None, report_contents=None):
+    del payload
+    run_id = run_id or str(uuid.uuid4())
+    report_contents = report_contents or "hc-agent report"
+    runstore = RunStore(runstore_root)
+    runstore.write_report(run_id, report_contents)
+    return run_id
diff --git a/tests/test_hc_agent_smoke.py b/tests/test_hc_agent_smoke.py
new file mode 100644
index 0000000000..8b5e76abcd
--- /dev/null
+++ b/tests/test_hc_agent_smoke.py
@@ -0,0 +1,38 @@
+from unittest import mock
+
+import hc_agent
+
+
+class FakeResponse:
+    def __init__(self, status_code=200, json_data=None):
+        self.status_code = status_code
+        self._json_data = json_data or {}
+
+    def json(self):
+        return self._json_data
+
+
+def test_preview_does_not_call_requests(monkeypatch):
+    def raise_if_called(*args, **kwargs):
+        raise AssertionError("should not call")
+
+    monkeypatch.setattr(hc_agent.requests, "request", raise_if_called)
+    result = hc_agent.preview({"run": "preview"})
+    assert result["mode"] == "preview"
+
+
+def test_apply_calls_requests_once(monkeypatch):
+    fake_response = FakeResponse(status_code=202)
+    request_mock = mock.Mock(return_value=fake_response)
+    monkeypatch.setattr(hc_agent.requests, "request", request_mock)
+
+    response = hc_agent.apply({"run": "apply"})
+
+    assert response is fake_response
+    request_mock.assert_called_once()
+
+
+def test_gateway_writes_run_artifacts(tmp_path):
+    run_id = hc_agent.gateway_run({"run": "gateway"}, runstore_root=tmp_path)
+    report_path = tmp_path / "runs" / run_id / "report.md"
+    assert report_path.exists()