fix: fall back to jfjoch default when n_images_per_file is not configured

Reading jfjoch/n_images_per_file from aare config raises when the key is
not set and has no default (e.g. on x06da), which aborted data collection
setup. Treat a failed lookup like a missing config client: log a warning
and let JFJoch use its own images-per-file default.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/aare/devices/jfjoch.py

@@ -64,6 +64,19 @@ class JFJochWrapper:
             logger.exception("Failed to create aare config client")
             self._config_client = None
 
+    def _get_images_per_file(self) -> int | None:
+        """Images per file from aare config; None (JFJoch default) if unavailable."""
+        if self._config_client is None:
+            return None
+        try:
+            return self._config_client.jfjoch.n_images_per_file or None
+        except Exception:
+            logger.warning(
+                "jfjoch/n_images_per_file not available from aare config; using JFJoch default",
+                exc_info=True,
+            )
+            return None
+
     def connect(self) -> None:
         """Connect to JFJoch on first use; a no-op once the client exists."""
         if self._connected:
@@ -186,11 +199,7 @@ class JFJochWrapper:
             )
         else:
             smargon_phi_chi = None
-        images_per_file = (
-            self._config_client.jfjoch.n_images_per_file
-            if self._config_client is not None
-            else None
-        ) or None
+        images_per_file = self._get_images_per_file()
         dataset_settings = jfjoch_client.DatasetSettings(
             beam_x_pxl=s.diffraction.beam_center_pxl[0],
             beam_y_pxl=s.diffraction.beam_center_pxl[1],

tests/unit/devices/test_jfjoch.py

@@ -1,4 +1,4 @@
-from unittest.mock import MagicMock, patch
+from unittest.mock import MagicMock, PropertyMock, patch
 
 import pytest
 from aarecommon.errors.exception_handler import JFJochCommunicationError
@@ -123,6 +123,26 @@ def test_client_is_created_lazily(mock_jfjoch_client):
     assert wrapper._api is api
 
 
+def test_images_per_file_from_config(jfjoch_wrapper):
+    jfjoch_wrapper._config_client = MagicMock()
+    jfjoch_wrapper._config_client.jfjoch.n_images_per_file = 500
+    assert jfjoch_wrapper._get_images_per_file() == 500
+
+
+def test_images_per_file_without_config_client(jfjoch_wrapper):
+    jfjoch_wrapper._config_client = None
+    assert jfjoch_wrapper._get_images_per_file() is None
+
+
+def test_images_per_file_falls_back_when_key_not_set(jfjoch_wrapper):
+    # e.g. x06da, where jfjoch/n_images_per_file is not set and has no default
+    jfjoch_wrapper._config_client = MagicMock()
+    type(jfjoch_wrapper._config_client.jfjoch).n_images_per_file = PropertyMock(
+        side_effect=KeyError("jfjoch/n_images_per_file is not set and has no default")
+    )
+    assert jfjoch_wrapper._get_images_per_file() is None
+
+
 def test_initialize(jfjoch_wrapper, mock_jfjoch_client):
     mock_jfjoch_client.initialize_post.reset_mock()
     jfjoch_wrapper.initialize()