Can someone who experienced the issue on 17.4.x / 17.5.x confirm or deny it is solved for them on 18 / 17.6 beta? From my test, the same exact issue still exists on 18 beta.

As described above accurately, the issue is reproduced easily and consistently on all iOS versions after 17.4. Including iOS 18 beta and iOS 17.6 beta. It is true that the 30 seconds limit that happens on iOS 17.4 - 17.5.1 is not happening since the "fix" on iOS 18 beta, but the service worker still stop waking up to handle messages after a very short while (more than 30 seconds, but it it doesn't take long after exiting safari or locking/unlocking phone). Apple's repeated response of requesting feedback from developers about this issue is starting to look unprofessional as this is an issue that can clearly and easily demonstrated using the default template code for safari extension created by xcode.