This came up several years ago, and didn’t get anywhere: Database migration failure shouldn't block Syncthing auto-update. At that time, there was no way to politely ask Syncthing to upgrade.
In an ideal world I’d release a new synctrayzor version every time Syncthing does an incompatible change to its database or config file, but in practice I’ve no idea when this happens, and new releases are somewhat on the back burner since I stopped using Syncthing.
The problem with just grabbing Syncthing at install time (other than the additional failure modes) is that I’d need to (want to?) duplicate Syncthing’s signature checking logic. I’d rather just let Syncthing handle downloading and verifying an update: it knows what it’s doing better than I do.
What’s the best way to handle this? How should I detect this error (does it have its own error code?), and what exactly should I run to force it to upgrade there and then?