There is a sparkle-related 'issue' with the previous implementation. When you download/install in the `updateAvailable` state, if you don't install it, then check the updates again. Sparkle loses its downloaded stage in the delegate (it's normal when I use the sparkle source code). This time, when you click install in the `updateAvailable` state, it just uses the previous downloaded package and starts to install, without calling `showReady(toInstallAndRelaunch:)`.
I think removing `readyToInstall` in our customed ui, will reduce one step to install an update for most of the users out there, which makes sense, since the current package is pretty small, only takes a few seconds to download for a normal network, and they intended to install this update.
Ghostty now has a release channel build configuration. Current valid
values are "tip" and "stable" but I imagine more will be added in the
future.
The release channel is inferred whether the version we specify with the
`-Dversion-string` build flag has a prerelease tag or not. If it does,
the release channel is "tip". If it doesn't, the release channel is
"stable".
This also adds a configuration to specify the release channel for
auto-updates for the macOS application.
