fix(gateway): fall back to python3 when venv lacks bare python symlink

hermes_cli/gateway.py

@@ -720,11 +720,19 @@ def get_python_path() -> str:
     venv = _detect_venv_dir()
     if venv is not None:
         if is_windows():
-            venv_python = venv / "Scripts" / "python.exe"
+            candidates = [venv / "Scripts" / "python.exe"]
         else:
-            venv_python = venv / "bin" / "python"
-        if venv_python.exists():
-            return str(venv_python)
+            major_minor = f"python{sys.version_info.major}.{sys.version_info.minor}"
+            # uv-managed venvs may omit the bare ``python`` symlink, so fall
+            # back to ``python3`` / ``pythonX.Y`` before giving up on the venv.
+            candidates = [
+                venv / "bin" / "python",
+                venv / "bin" / "python3",
+                venv / "bin" / major_minor,
+            ]
+        for candidate in candidates:
+            if candidate.exists():
+                return str(candidate)
     return sys.executable
 
 

tests/hermes_cli/test_gateway_service.py

@@ -2,6 +2,7 @@
 
 import os
 import pwd
+import sys
 from pathlib import Path
 from types import SimpleNamespace
 
@@ -599,6 +600,61 @@ def test_returns_none_when_no_virtualenv(self, tmp_path, monkeypatch):
         assert result is None
 
 
+class TestGetPythonPath:
+    """Tests for get_python_path() interpreter resolution."""
+
+    def _make_venv(self, tmp_path, *names):
+        venv = tmp_path / "venv"
+        bin_dir = venv / "bin"
+        bin_dir.mkdir(parents=True)
+        for name in names:
+            (bin_dir / name).write_text("")
+        return venv
+
+    def test_prefers_bare_python_when_available(self, tmp_path, monkeypatch):
+        venv = self._make_venv(tmp_path, "python", "python3", "python3.11")
+        monkeypatch.setattr(gateway_cli, "_detect_venv_dir", lambda: venv)
+        monkeypatch.setattr(gateway_cli, "is_windows", lambda: False)
+
+        result = gateway_cli.get_python_path()
+        assert result == str(venv / "bin" / "python")
+
+    def test_falls_back_to_python3_when_bare_python_missing(self, tmp_path, monkeypatch):
+        # Reproduces the uv-managed venv layout that broke systemd ExecStart:
+        # no bare ``python`` symlink, only ``python3`` / ``pythonX.Y``.
+        venv = self._make_venv(tmp_path, "python3", "python3.11")
+        monkeypatch.setattr(gateway_cli, "_detect_venv_dir", lambda: venv)
+        monkeypatch.setattr(gateway_cli, "is_windows", lambda: False)
+
+        result = gateway_cli.get_python_path()
+        assert result == str(venv / "bin" / "python3")
+
+    def test_falls_back_to_versioned_python(self, tmp_path, monkeypatch):
+        major_minor = f"python{sys.version_info.major}.{sys.version_info.minor}"
+        venv = self._make_venv(tmp_path, major_minor)
+        monkeypatch.setattr(gateway_cli, "_detect_venv_dir", lambda: venv)
+        monkeypatch.setattr(gateway_cli, "is_windows", lambda: False)
+
+        result = gateway_cli.get_python_path()
+        assert result == str(venv / "bin" / major_minor)
+
+    def test_returns_sys_executable_when_venv_has_no_interpreter(self, tmp_path, monkeypatch):
+        venv = self._make_venv(tmp_path)  # empty bin dir
+        monkeypatch.setattr(gateway_cli, "_detect_venv_dir", lambda: venv)
+        monkeypatch.setattr(gateway_cli, "is_windows", lambda: False)
+        monkeypatch.setattr("sys.executable", "/opt/fallback/python")
+
+        result = gateway_cli.get_python_path()
+        assert result == "/opt/fallback/python"
+
+    def test_returns_sys_executable_when_no_venv_detected(self, monkeypatch):
+        monkeypatch.setattr(gateway_cli, "_detect_venv_dir", lambda: None)
+        monkeypatch.setattr("sys.executable", "/usr/bin/python3")
+
+        result = gateway_cli.get_python_path()
+        assert result == "/usr/bin/python3"
+
+
 class TestSystemUnitHermesHome:
     """HERMES_HOME in system units must reference the target user, not root."""