Element tokens (ui_tool/ui_thinking), skinnable diffs, and code-syntax keys
flow through buildPalette → adaptColorsToBackground instead of a hand-mapped
color block, so they inherit #20379's contrast/polarity machinery. thinking
and syntaxComment track the EFFECTIVE muted (banner_dim override included);
the skin's `background` feeds the surface (it also paints the terminal via
OSC 11); statusFg falls back through ui_text/banner_text. Tests assert the
routing/independence contracts rather than pre-adaptation hexes.
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