feat: implement slot_error_boundary decorator and add unit tests for session and device controllers

src/pygui/backend/utils.py

@@ -0,0 +1,29 @@
+import logging
+from functools import wraps
+
+
+def slot_error_boundary(func):
+    """Wrap a @Slot method so exceptions are logged + signalled to QML.
+
+    Usage (stack under @Slot):
+        @Slot()
+        @slot_error_boundary
+        def myMethod(self) -> None:
+            ...
+
+    On exception:
+      - Logs full traceback via logger.exception()
+      - Emits logMessage signal with human-readable error (if available)
+      - Returns None so QML never sees a crash
+    """
+    @wraps(func)
+    def wrapper(self, *args, **kwargs):
+        try:
+            return func(self, *args, **kwargs)
+        except Exception as e:
+            logger = logging.getLogger(self.__class__.__module__)
+            logger.exception("Slot '%s' raised: %s", func.__name__, e)
+            if hasattr(self, "logMessage"):
+                self.logMessage.emit(f"Error in {func.__name__}: {str(e)}")
+            return None
+    return wrapper