Apply the existing theme selectionBg token to the plain <text> content
renderables (TextBufferRenderable supports selectionBg/selectionFg) so a
selection draws a clean solid bar that PRESERVES the text fg (no selectionFg →
no SGR-inverse fragmenting). Applied to:
- messageLine: the flat settled/user/system message text.
- toolPart: the args value lines + the output body lines.
Limitation: assistant answers rendered via the native <markdown> renderable
(MarkdownRenderable extends Renderable, not TextBufferRenderable, and
MarkdownOptions has no selectionBg/selectionFg) cannot take the themed highlight
— they fall back to the renderer's default selection style.
alt-glitch
76e9271dce