The proposed solution to mitigate covert-channel attacks in differential privacy systems involves using predictable transactions. This method enforces that each query or sub-query completes within a predefined time frame, regardless of the actual data being processed. If a query cannot be completed in the allotted time, it is aborted and a default value is returned. This approach prevents attackers from gaining information based on query execution time or other observable side effects, preserving the integrity of the differential privacy guarantees.