In a burst of non-thinking enthusiasm I sandboxed then sparkle-updated my app. Since the app only has read/write access to user selected files (and the music directory) I can't now update my own binary. Oops.
This has been extensively debated with Andy Matuschak over the last year or so (https://github.com/sparkle-project/Sparkle/pull/165) but while the proposed solutions are 'nearly good enough', no light has been shed on the problem of having already distributed a non-sandboxed app.
Oh, and it appears it might be relevant that I've been using the 'disk image' method of sparkle distribution.
The only solution AT ALL that I can think of is to release a sparkle update that just presents a message to the users telling them to manually download. Does anyone have any better ideas?
-Dave