fix(triplet-store): preserve missing backend dependency errors

semantica/triplet_store/triplet_store.py

@@ -156,9 +156,11 @@ class TripletStore:
 
             self.logger.info(f"Initialized {self.backend_type} backend")
 
+        except ImportError:
+            raise
         except Exception as e:
             self.logger.error(f"Failed to initialize {self.backend_type} backend: {e}")
-            raise ProcessingError(f"Failed to initialize backend: {e}")
+            raise ProcessingError(f"Failed to initialize backend: {e}") from e
 
     def store(
         self,

tests/triplet_store/test_oxigraph_store.py

@@ -158,4 +158,4 @@ def test_missing_optional_dependency_has_install_hint():
         side_effect=import_without_oxigraph,
     ):
         with pytest.raises(ImportError, match="tripletstore-oxigraph"):
-            OxigraphStore()
+            _store()