some fixes and improvements

python_app/hardware_full/sn9000_service.py

@@ -10,12 +10,15 @@ synchronized SCPI round trip.
 from __future__ import annotations
 
 from dataclasses import dataclass, field
+import logging
 import time
 from typing import Any
 
 import numpy as np
 import pyvisa
 
+logger = logging.getLogger(__name__)
+
 from python_app.models.dataset_model import ComboKey, SweepCollection, TraceData
 from python_app.models.run_config_model import RadarSweepModel
 
@@ -324,7 +327,12 @@ class Sn9000Service:
             try:
                 instrument.read_bytes(1, break_on_termchar=True)
                 return
-            except Exception:
+            except pyvisa.errors.VisaIOError as exc:
+                # Timeouts on a trailing newline are routine; anything else
+                # likely means HiSLIP framing is out of sync and the next
+                # request will hang — surface it in the logs.
+                if exc.error_code != pyvisa.constants.StatusCode.error_timeout:
+                    logger.warning("SN9000 terminator drain failed: %s", exc)
                 return
 
     def _read_response_bytes(self, count: int) -> bytes: