The Loader baked the advancing braille glyph into the underlying Text
via setText, so Text.render's wrap cache (keyed on text) missed every
80ms tick and re-ran wrapTextWithAnsi plus per-line width measurement
over the whole message even though only a 1-cell glyph changed. On a
single-subagent hub wait the direct-write render loop consumed ~48% of
a saturated core.
The wrapped text now carries a stable sentinel glyph (frames[0]); the
spinner advance only bumps the frame index and requests a repaint, and
render() swaps the visible glyph over the cached layout. wrapTextWithAnsi
and stringWidth now run only when the message actually changes.
Fixes#6940
(cherry picked from commit 6ec38053ebc1e33859358df3b66f71fea27532c7)
