fix: modernize dependency recovery guidance (#5282)

tests/providers/test_openai_compat_timeout.py

@@ -1,5 +1,6 @@
 from unittest.mock import patch, sentinel
 
+from nanobot.providers import openai_compat_provider
 from nanobot.providers.openai_compat_provider import OpenAICompatProvider
 from nanobot.providers.registry import ProviderSpec
 
@@ -59,3 +60,22 @@ async def test_openai_compat_provider_timeout_can_be_overridden_by_env(monkeypat
         await provider._ensure_client()
 
     assert mock_async_openai.call_args.kwargs["timeout"] == 45.0
+
+
+async def test_missing_langfuse_warning_recommends_plugin_command(monkeypatch) -> None:
+    monkeypatch.setenv("LANGFUSE_SECRET_KEY", "secret")
+    monkeypatch.setattr(openai_compat_provider, "AsyncOpenAI", None)
+
+    with (
+        patch("importlib.util.find_spec", return_value=None),
+        patch("openai.AsyncOpenAI") as mock_async_openai,
+        patch("nanobot.providers.openai_compat_provider.logger.warning") as mock_warning,
+    ):
+        provider = OpenAICompatProvider(api_key="test-key", api_base="https://example.com/v1")
+        await provider._ensure_client()
+
+    mock_warning.assert_called_once_with(
+        "LANGFUSE_SECRET_KEY is set but langfuse is not installed; "
+        "run `nanobot plugins enable langfuse` to enable tracing"
+    )
+    mock_async_openai.assert_called_once()