Update a Static, and relayout only when the content width changes.
Static.update relayouts the whole screen by default. That reflows every
mounted transcript widget, so a 10 Hz spinner gets slower as the
transcript grows. A spinner tick swaps one glyph at the same cell width,
so a repaint is sufficient. A width change (for example, the elapsed time
grows from (59s) to (1m 0s)) still relayouts, so width: auto
widgets resize and wrapped lines reflow.
