0593 — the night board, chosen from the footer

Context

[0583] kept visited-purple links and deferred dark mode to a “Board style” dropdown, not a system toggle. The footer already rendered the chrome for it — Board style: Vulkan Classic ▾ as an inert chip — and the donor was left open.

The tokens layer was ready: all 42 component stylesheets carry zero raw colours (stylelint’s declaration-strict-value enforces it), so no component has to change for a second palette to exist.

Decision

A second board style, night, selected by a real <select> in the footer and carried on <html> as data-board-style.

The donor is the era’s dark-board convention rather than the site’s own volcano: near-black content ground under navy chrome, silver text, accents lifted until they carry. Amber is NOT part of the palette swap — “amber means new-or-act and nothing else” is [0583]‘s rule, and a style may not give that mark a second meaning, so the night sheet inherits the classic amber primitives untouched and only darkens the grounds they sit on.
A style is its own primitive sheet plus a re-point of the semantic names the components already consume; the primitive names stay honest about their own colours (--surface-coal, --band-slate-start, --link-sky) instead of one hue-named sheet lying under two palettes. Everything structural — the grid, the z-index scale, the fonts — is style-independent and stated once.
Shiki is the ONE thing a token swap cannot reach: it highlights at build time and would bake one style’s colours into every fence. Both themes now ship with defaultColor: false, so Shiki writes --shiki-light / --shiki-dark per token and the base layer picks the side. That is a board style read outside the tokens layer, and website/CONVENTIONS.md records it as the one sanctioned crossing.
An is:inline script in BoardLayout’s <head> puts the style on <html> before the first paint, and again on astro:after-swap: ClientRouter [0592] copies the incoming document’s <html> attributes, and the incoming document is the static build, which carries none. It re-reads storage each time, so a choice made in the footer survives the next navigation.
Until a reader chooses, prefers-color-scheme picks the opening style. Once they choose, the stored value outranks the operating system for good — the system seeds, it does not toggle.

Consequences

Contrast in night matches the style it mirrors rather than improving on it: ink-faint reads 3.50 against its ground in both sheets, the SQL comment 3.68 against classic’s 3.31, the null cell 2.70 against classic’s 1.99. Raising any of them is one change touching both sheets, never a night-only fix that makes the two styles disagree.
BoardFooter is an island now (client:idle) — a <select> in static HTML does nothing. Cost is 1.6 KB raw / 0.8 KB gzipped on every page; the Svelte runtime was already there for the visit bar.
A third style is another primitive sheet plus another ~65 semantic re-points, kept in sync by hand. Two is the settled menu.
Storybook gets the style as a toolbar global rather than a second story per component: every component has as many looks as the board has styles, and doubling 40-odd story files to say so is not a checklist, it is noise.