fix(harness): import fi.simulate on the callback adapter's main thread

src/fi/alk/harness/callback_http_adapter.py

@@ -17,6 +17,9 @@
 from http.server import BaseHTTPRequestHandler, ThreadingHTTPServer
 from typing import Any
 
+# Main thread only: with livekit installed this import registers plugins.
+from fi.simulate import AgentInput
+
 
 def _load_callback() -> Any:
     target = os.environ["ALK_CALLBACK_ENTRYPOINT"]
@@ -46,8 +49,6 @@ def _json_body(value: Any) -> dict[str, Any]:
 
 
 def _invoke(payload: dict[str, Any]) -> dict[str, Any]:
-    from fi.simulate import AgentInput
-
     result = CALLBACK(AgentInput.model_validate(payload))
     if inspect.isawaitable(result):
         result = asyncio.run(result)

tests/harness/test_callback_http_adapter.py

@@ -0,0 +1,73 @@
+import json
+import os
+import socket
+import subprocess
+import sys
+import time
+import urllib.request
+from pathlib import Path
+
+import pytest
+
+ADAPTER = (
+    Path(__file__).resolve().parents[2] / "src/fi/alk/harness/callback_http_adapter.py"
+)
+
+
+def _free_port() -> int:
+    with socket.socket() as probe:
+        probe.bind(("127.0.0.1", 0))
+        return probe.getsockname()[1]
+
+
+@pytest.fixture
+def adapter(tmp_path):
+    (tmp_path / "chat_agent.py").write_text(
+        "def reply(agent_input):\n"
+        "    return {'content': 'thread ' + agent_input.thread_id}\n",
+        encoding="utf-8",
+    )
+    # Bundles embed the adapter's source and run it from the bundle, not from the package.
+    script = tmp_path / "adapter.py"
+    script.write_text(ADAPTER.read_text(encoding="utf-8"), encoding="utf-8")
+    port = _free_port()
+    process = subprocess.Popen(
+        [sys.executable, str(script)],
+        env={
+            **os.environ,
+            "ALK_CALLBACK_ENTRYPOINT": "chat_agent:reply",
+            "PORT": str(port),
+            "PYTHONPATH": str(tmp_path),
+        },
+        stderr=subprocess.PIPE,
+    )
+    base = f"http://127.0.0.1:{port}"
+    deadline = time.monotonic() + 30
+    while time.monotonic() < deadline:
+        try:
+            urllib.request.urlopen(f"{base}/health", timeout=1)
+            break
+        except OSError:
+            if process.poll() is not None:
+                pytest.fail(process.stderr.read().decode())
+            time.sleep(0.2)
+    yield base
+    process.terminate()
+    process.wait(timeout=10)
+
+
+def test_a_callback_answers_from_the_request_thread(adapter):
+    """The request thread is not the main thread; nothing imported there may require it."""
+    body = json.dumps(
+        {
+            "thread_id": "t1",
+            "messages": [{"role": "user", "content": "hello"}],
+            "new_message": {"role": "user", "content": "hello"},
+        }
+    ).encode()
+    request = urllib.request.Request(
+        f"{adapter}/invoke", data=body, headers={"Content-Type": "application/json"}
+    )
+    with urllib.request.urlopen(request, timeout=30) as response:
+        assert response.status == 200
+        assert json.loads(response.read())["content"] == "thread t1"