The KVO callback was calling updateLayout(), which has two problems for
content-driven updates:
1. The prevLayoutDetentIdentifier guard can block updates. When
updateDetents triggers animateChanges, the delegate callback
sheetPresentationControllerDidChangeSelectedDetentIdentifier fires
and updates selectedDetentIdentifier to the system-assigned custom
detent identifier. On the next KVO callback, prevLayoutDetentIdentifier
(.medium) no longer matches selectedDetentIdentifier, so the update
is silently dropped.
2. Re-reading frame.size.height from the view hierarchy instead of using
the observed bounds can return a stale value during rapid layout passes.
Fix: have the KVO callback call updateDetents directly with the observed
height, bypassing both the guard and the frame re-read. The guard in
updateLayout() is preserved for the manual/fallback code path.
https://claude.ai/code/session_01Rp7ef1h3fKh6fhStcjqLJ5
Claude
421c4abd02