Is there an existing issue for this?

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Steps to reproduce

Currently the Cupertino back gesture assumes its pop will always remove the route, however it missed the case where onPopPage can still veto the pop. Right now, this will cause the page to hang.

The question is what should they do in this case. I can think several ways forward.

1. onPopPage can veto the pop, then we have to fix the cupertino back swipe to not freeze the screen if it is veto'd
2. page based route will disable cupertino back swipe.
3. cupertino backswipe can't be veto by onPopPage.

It seems to me (2) or (3) is closer to the current cupertino back swipe behavior, but (2) may be too aggressive. If we want to implement (3) we will need a new API in Navigator to still give customer a chance to clean up their page list.

Actual results

fix the issue.

Logs

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Flutter Doctor output

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