Truncation was measured once on mount and watched through a ResizeObserver
on the clamped element, whose own height stops changing under line-clamp.
A message measured before its content settled never regained the expand
affordance, and a just-sent one measured before its turn finished laying
out could not be expanded at all.
Measure at click time so expanding depends on whether the text is clipped
right now, re-read once on the next frame after mount, and observe the
children (which keep their natural height) plus subtree swaps.
Bohdan Triapitsyn
11d7c7b481