[w-goog]

(Fresh-branch version of #917 by @Prash88)

On cancel, ASWebAuthenticationSession's completion handler runs before its dismiss transition starts (this is an apple bug, radar is linked at the end). We dropped our last reference inside that handler, so the transition's completion block later released an already-freed SFAuthenticationSession - EXC_BAD_ACCESS once the sheet finished animating.

At each release point the session goes to a main-queue block that holds it for one turn + 2s. The delay starts once the main queue is next free, so a slow completion callback doesn't eat into it (2s is a guess, there's no real API to observe the transition).

I also tried the messy option of inspecting the transitionCoordinator to time against the animation, but the crash happened before that was available.

Not covered here: the Catalyst agent has the same handler pattern. There's no unit test, as dealloc timing isn't unit-testable.

Verified on the iOS 26.4 simulator: 3 cancels via the #917 repro, no crash.

Radar link: https://openradar.appspot.com/FB12132525
Dev forum workaround link: https://developer.apple.com/forums/thread/123667

Note to reviewer: Sent you some additional internal context on chat.