Importing a save file
Settings now has a Saves tab with an Import option. It opens the system file picker and the app copies the save into place itself, so bringing a save over from another device or a backup no longer needs adb or a file manager that can reach Android/data.
The file is checked before anything is replaced. It has to be the right size and actually contain Goemon save data, so a save for a different game, or a flash dump from another emulator that happens to be the same size, is refused rather than imported. Whatever save was already there is kept alongside the new one as a .pre-import.bak file, so an import can be undone by renaming that file back.
Importing is only possible before you start the game. Once it is running the game holds your save in memory and writes it back out as it goes, so a file swapped underneath it would be overwritten.
Saving failures now say what went wrong
"Failed to write to the save file" used to be the same sentence whatever had actually gone wrong. It now names the exact file it tried to write and what the system said about it. If you run into save trouble, that message is the useful thing to include in a bug report.