correctness

When caching lists, include inputs that change the list (filters, page, member permissions). A deterministic cache key function prevents subtle “wrong user saw wrong list” bugs.

If you sort by a non-unique column (score, created_at), pagination can “skip” or “duplicate” records. Always add a secondary unique key like id for deterministic ordering.

Scheduling bugs are often time zone bugs. Persist times in UTC, accept user input in their zone, and convert explicitly. Keep conversions close to the boundary (forms/controllers).