some fixes again

python_app/hardware_full/librevna_service.py

@@ -3,11 +3,14 @@
 from __future__ import annotations
 
 from dataclasses import dataclass, field
+import logging
 
 from python_app.hardware_full.librevna_backends import LibreVnaBackend, MockLibreVnaBackend, NativeLibreVnaBackend
 from python_app.hardware_full.librevna_driver.models import SweepResult
 from python_app.models.run_config_model import RadarSweepModel
 
+logger = logging.getLogger(__name__)
+
 
 @dataclass(slots=True)
 class LibreVnaService:
@@ -41,9 +44,16 @@ class LibreVnaService:
                 strict_protocol_version=self.strict_protocol_version,
             )
             self._driver_available = True
-        except Exception:
+        except Exception as exc:
+            # 'native' demands real hardware — never substitute synthetic data.
             if mode == "native":
                 raise
+            # 'auto' falls back to the mock backend ONLY when the native driver
+            # library itself is unavailable (a dev host without the USB stack) —
+            # this is not device-absence (that surfaces later from open()). Log it
+            # loudly so it is never a silent surprise; a deployed appliance should
+            # set driver_mode='native' to forbid the fallback entirely.
+            logger.warning("LibreVNA native backend unavailable; falling back to mock (mode=auto): %s", exc)
             self._backend = MockLibreVnaBackend()
             self._using_mock_backend = True