The alpha and experimental builds are now also available on Steam, Itch.io and via zeroinstall, because why not. Which lead to another annoying macOS problem; after updates, the game would no longer run on Steam and Itch, sometimes. Steam gives "OS Error 4294956470", Itch just doesn't open the game, and if you try to start it manually over the file system, you get a "Permission Denied" error. Completely wiping and reinstalling the game helps (as you find out by googling the error message, it's quite common). Interestingly, if you copy the broken, installed app bundle elsewhere, it runs flawlessly, so it's not data corruption; none of the diagnostic tools I learned about would tell me why the game would not run in its original place. My suspicion: Itch and Steam update the app bundle in place, changing file after file. In the intermediate stages of that process, the signature is bound to be invalid. Sometimes, Gatekeeper must notice that and put a hidden "Bad, Verboten" flag onto the bundle.
As a workaround, for Itch, the whole app bundle gets the version added to its name. Itch does not mind and starts whatever is in your archive, and Gatekeeper does not see one app bundle getting corrupted, it sees a new bundle getting created, which seems to be fine. Did I mention already that I love the way Itch works? There is no song and dance, you just tell its upload tool 'butler' you have a new build in this directory and which release channel it goes to, you don't even have to configure the channel beforehand and if you give it a sensible name, it deduces what system it is for.
Anyway, doing that on Itch still keeps the download patch size between versions small, somehow. And Itch has an interesting quirk: If you upgrade to a later version, old files that no longer are in the new version are removed. But if you go BACK to a previous version,






Steam is more stuck up, you have to have a fixed executable or app bundle name to launch. So there, all I can do is rename the executable while keeping the app bundle name the same. Seems to be enough to work around the problem.
Edit, I forgot: Two improvements fell out of this: The previous attempts to get macOS to understand that 0.2.9 with SDL 1.2 does not understand Retina displays now work after the App Bundle restructure (another fine example of unhelpful diagnostics); no more need to use an old SDK to get functional builds. And the user data is now (again) properly stored in the default macOS place (Library/Application Support, I think it was); that was required to make the Itch Sandbox work.