bug(cdkDrag): Items in DropLIst Jump Down When Using DragBoundary or ConstrainPosition with Custom Preview

[bklopcic]

Is this a regression?

• Yes, this behavior used to work in the previous version

The previous version in which this bug was not present was

No response

Description

Items with a custom preview inside of a drop list that should be constrained either by constrainPosition or a dragBoundary appear to jump down for one frame when being dragged before constraint is applied.

Reproduction

StackBlitz link: https://stackblitz.com/edit/stackblitz-starters-eyxb1gn5?file=src%2Fmain.ts

Expected Behavior

Constraints are applied to drag preview on starting frame of drag.

Actual Behavior

Constraints are not applied to drag preview until the second frame of the dragging.

Environment

• Angular: 19.0.6
• CDK/Material: 19.1.2
• Browser(s): Chrome/Firefox
• Operating System (e.g. Windows, macOS, Ubuntu): Windows

[bklopcic]

Came up with this pretty undesirable workaround: https://stackblitz.com/edit/stackblitz-starters-5wo1dru6?file=src%2Fmain.ts

I'm manually setting the preview element's transform on drag start.

I also found resolved issue #25154 that sounds very similar... but I tried reverting to the version that should have contained the fix and was still encountering my issue.

-- edit: this solution does not seem to work on mobile