Make a partly-undone import retryable, and refuse a plan it cannot deliver

shopdb/core/api/settings.py

@@ -701,6 +701,7 @@ def winc_import_batches():
 def winc_import_undo():
     """Reverse an applied WINC import batch by id. Conservative and reversible."""
     from shopdb.core.services.wincimport import undo as winc_undo
+    from shopdb.core.services.wincimport import WincImportError
 
     payload = request.get_json(silent=True) or {}
     batchid = (payload.get('batchid') or request.form.get('batchid') or '').strip()
@@ -714,7 +715,10 @@ def winc_import_undo():
             changes={'batchid': batchid, 'reverted': result['reverted'],
                      'conflicts': len(result['conflicts'])})
         db.session.commit()
-    except ValueError as exc:
+    except (ValueError, WincImportError) as exc:
+        # WincImportError too: refusing a batch of another importer's kind is a
+        # bad request, not a server fault. Preview and commit already catch it;
+        # this route did not, so the refusal surfaced as a 500.
         db.session.rollback()
         return error_response(ErrorCodes.VALIDATION_ERROR, str(exc))
     except Exception: