My Feedback was marked as "Investigation complete - Unable to diagnose with current information"

It was probably a mistake to mention this in a place where Apple Safari extension engineers can see it, because they might just quash your technique. ;-)

Sorry, I didn't look at your demo video before. I think I can reproduce your results now. The redirect works the first time I search from the address bar (although the web page crashes in Safari 17.6), but it doesn't work the second time, after a page is already loaded in the tab. Note that if you change the focus away from the address bar, you can see it's stuck in the middle of page loading progress.

The workaround is in the sample Xcode project.

It's actually a Safari app extension, so there's no manifest.json file.

Hmm, I'm still using V2. I wonder if that makes a difference.

As I said a month ago, it's too late. I already made the difficult decision to discontinue my app and remove it from the Mac App Store. I'm not going to reverse the decision now, especially since it's clear that this feature has a very low priority within Apple and may be broken without care or comment.

Let me put it this way: "The API is not retired, but it's completely nonfunctional now" is not a coherent position. Also, once developers dump the API, either by adopting 3rd party code, or by removing features from their software, they are NEVER coming back to this API. You lose our trust in this very acute way, and that's it, nobody in their right mind would ever come back. So as I said, the API seems to be retired now, is it not?

It appears that their "workaround" is to dump the DNSService API and adopt the 3rd party TCMPortMapper framework. The response "OK, cool" to that is... not cool. Does Apple not care at all about binary compatibility on the Mac anymore? I personally reported this bug in Feedback Assistant the first week of WWDC. As Lucky7 said, "If you want to retire the API, just say so." The API has been effectively retired in Monterey, whether Apple has announced it or not. You are correct that "Apple’s engineering sets their own priorities", and it's quite obvious from their actions — err, inaction — that they've chosen to ignore this API, so why don't they just say so? Developers who are using the API need guidance desperately right now.

My internalPort is as expected FWIW.