bug: reorder swap boundaries drift with fractional row heights #31670

Prerequisites

• I have read the Contributing Guidelines.
• I agree to follow the Code of Conduct.
• I have searched for existing issues that already report this problem, without success.

Ionic Framework Version

v9.x

Current Behavior

With fractional-height rows, the point at which dragged items swap drifts further out of alignment down the list. Reordering behaves normally near the top, but becomes noticeably incorrect further down.

Expected Behavior

The swap point should stay consistent regardless of the row's position in the list.

Steps to Reproduce

1. Open the reproduction, which renders 300 rows with a 64.5px-high content block in each item.
2. Drag a row near the top and observe the swap point.
3. Scroll to around row 60, then row 120, and repeat. The swap point becomes increasingly displaced.
4. Change the content block height from 64.5px to 65px. The drift disappears.

Code Reproduction URL

https://stackblitz.com/edit/cbvwwfdc?file=src%2Fapp%2Fexample.component.html

Ionic Info

Reproduction dependencies: @ionic/angular 9.0.10, @ionic/core 9.0.10, Angular ^22.0.0, ionicons 8.1.0.

This is the output from running npx --yes --package=@ionic/cli ionic info in the StackBlitz terminal:

Ionic:

   Ionic CLI : 7.2.1

Utility:

   cordova-res : not installed globally
   native-run  : not installed globally

System:

   NodeJS : v22.22.3
   npm    : 10.8.2
   OS     : Linux 5.0

Additional Information

The reorder group sums child.offsetHeight to cache row boundaries. A rendered height of 64.5px is rounded to 65px, accumulating a 0.5px error per row. In the affected app, the measured boundary error reaches 31.5px after 63 rows. Forcing whole-pixel row heights fixes the behavior.