fix: validate WebUI launcher can import agent

tests/test_bootstrap_python_selection.py

@@ -0,0 +1,42 @@
+import pathlib
+
+import bootstrap
+
+
+def test_ensure_python_prefers_agent_venv_when_launcher_cannot_import_agent(monkeypatch, tmp_path):
+    """Avoid starting WebUI with a local venv that later cannot import AIAgent."""
+    local_python = tmp_path / "webui" / ".venv" / "bin" / "python"
+    agent_python = tmp_path / "agent" / "venv" / "bin" / "python"
+    agent_python.parent.mkdir(parents=True)
+    agent_python.write_text("", encoding="utf-8")
+
+    probes = []
+
+    def fake_can_run(python_exe: str, agent_dir: pathlib.Path | None = None) -> bool:
+        probes.append(pathlib.Path(python_exe))
+        return pathlib.Path(python_exe) == agent_python
+
+    monkeypatch.setattr(bootstrap, "_python_can_run_webui_and_agent", fake_can_run)
+
+    selected = bootstrap.ensure_python_has_webui_deps(str(local_python), tmp_path / "agent")
+
+    assert selected == str(agent_python)
+    assert probes == [local_python, agent_python]
+
+
+def test_ensure_python_fails_loudly_when_no_interpreter_can_import_agent(monkeypatch, tmp_path):
+    """Do not report health OK when chat would fail with missing AIAgent."""
+    local_python = tmp_path / "webui" / ".venv" / "bin" / "python"
+    agent_python = tmp_path / "agent" / "venv" / "bin" / "python"
+    agent_python.parent.mkdir(parents=True)
+    agent_python.write_text("", encoding="utf-8")
+
+    monkeypatch.setattr(bootstrap, "_python_can_run_webui_and_agent", lambda *a, **k: False)
+    monkeypatch.setattr(bootstrap.subprocess, "run", lambda *a, **k: None)
+
+    try:
+        bootstrap.ensure_python_has_webui_deps(str(local_python), tmp_path / "agent")
+    except RuntimeError as exc:
+        assert "cannot import both WebUI dependencies and Hermes Agent" in str(exc)
+    else:
+        raise AssertionError("expected RuntimeError")