Hide the dialog. Call BEFORE appending it to the scene — after that it is too late, because the frame this exists to suppress has already been painted.

Show the dialog. Idempotent, and safe on one that was never hidden — both matter, because the failsafe path calls this on every dialog regardless.

Lay the dialog out now that it is attached, then show it.

The forced settleLayout is what makes this immediate rather than eventual. It is also harmless when the dialog already laid itself out while its fields were being set (the common case): applyLayout is idempotent, and re-running it against measurements that have not changed produces the same geometry.