Start with the session structure. A short puzzle may save completed levels. A longer adventure may need checkpoints, inventory, story decisions, and settings. Define the actual state rather than use “save everything” as the specification.
Decide when saving happens
Automatic saves, explicit saves, and checkpoint systems create different expectations. Communicate important limitations clearly. If leaving during a sequence loses recent progress, the player should have a reasonable way to understand that consequence.
Plan for missing, damaged, or outdated data. The appropriate response depends on the game, but it should be considered before release. Updates can change the data structure, so compatibility and migration need attention when existing players are involved.
Test the awkward moments
Resume after ordinary exits and interruptions on the actual target platform. Check settings as well as progress. Test a new install and an update from a relevant older build. A successful save in the editor does not establish the behavior of every exported build or device.
Document the chosen rules and known limits. Cloud synchronization, account recovery, and cross-device progress are separate systems with additional dependencies. A clear, reliable local save can be more valuable than an ambitious promise whose interruption and recovery behavior has never been tested.