UISheetPresentationController's per-detent backgroundEffect doesn't transition during interactive drags

I'm using the new per-detent backgroundEffect (iOS 26.1+) on UISheetPresentationControllerDetent. When the user drags the sheet between two detents with different effects, nothing changes during the drag; the previous detent's effect stays until the finger lifts, then a fixed-length cross-fade runs on its own, decoupled from the sheet's settle animation. It reads as a jump.

Minimal setup (form sheet, nothing else):

UISheetPresentationControllerDetent *medium = [UISheetPresentationControllerDetent mediumDetent];
UISheetPresentationControllerDetent *tall =
  [UISheetPresentationControllerDetent customDetentWithIdentifier:@"c90"
      resolver:^CGFloat(id<UISheetPresentationControllerDetentResolutionContext> ctx) {
        return ctx.maximumDetentValue * 0.9;
    }];
medium.backgroundEffect = nil;
tall.backgroundEffect = [UIColorEffect effectWithColor:UIColor.systemBackgroundColor];
sheet.detents = @[ medium, tall ];

Expected: the effect transition is driven by the drag progress between adjacent detents, or at least runs inside the same settle animation as the height change.

Reproduces on iOS 26.5 (23F77) and 27.0 (24A434) Simulator with iPhone 17 Pro, iOS 27.1 (24A94401) Simulator with iPhone Duo. Xcode 27.1.

Is this intended, and is there a supported way to tie the per-detent effect transition to the gesture? Filed as FB25459597.