more house keeping

dynamodb/transact.odin

@@ -333,7 +333,31 @@ transact_write_items :: proc(
 			}
 		}
 
-		existing, _ := get_item_internal(engine, action.table_name, key_item, metadata)
+		existing, read_err := get_item_internal(engine, action.table_name, key_item, metadata)
+		#partial switch read_err {
+			case .None:
+				// Item found or not found — both fine.
+			case .RocksDB_Error, .Serialization_Error, .Internal_Error:
+				// Cannot safely determine old index keys — cancel the entire transaction.
+				reasons[idx] = Cancellation_Reason{
+					code    = "InternalError",
+					message = "Failed to read existing item for index maintenance",
+				}
+				result.cancellation_reasons = reasons
+				return result, .Internal_Error
+			case .Missing_Key_Attribute, .Invalid_Key:
+				// The key we built from the action's own item/key should always be valid
+				// by this point (validated earlier), but treat defensively.
+				reasons[idx] = Cancellation_Reason{
+					code    = "ValidationError",
+					message = "Invalid key when reading existing item",
+				}
+				result.cancellation_reasons = reasons
+				return result, .Internal_Error
+			case .Table_Not_Found, .Item_Not_Found, .Validation_Error:
+				// These should not be returned by get_item_internal, but handle
+				// defensively — treat as "item does not exist" and continue.
+		}
 		old_items[idx] = existing
 	}