docs(theme-studio): spec palette ramp generation + background-contrast safety

Design doc (spec-create workflow) for two coupled v1 features: generating a harmonized tonal ramp from a base color, and a worst-case-contrast readout that caps a background tint at the lightness where every foreground on it stays readable. Cross-linked from the color-harmony task; harmonic fill deferred to vNext.

1 files changed, 3 insertions, 1 deletions

diff --git a/todo.org b/todo.org
index 18fd7205..d0920ea8 100644
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@@ -71,7 +71,9 @@ Two features it enables (both worth building):
 1. Ramp generation (focus first): from a base color, generate its tonal ramp — base, +1/+2/+3 (lighter) and -1/-2/-3 (darker) — by stepping OKLCH lightness (and easing chroma) on a fixed hue. Term note: the whole family is a "ramp"/"tonal scale"; darker steps are "shades", lighter are "tints", gray-mixed are "tones" — so "ramp" or "scale" is the precise word, not "shades".
 2. Harmonic fill: from a few chosen colors (e.g. slate blue + bg), generate a table of harmonic candidates (hue-angle schemes at matched L/C) to fill the missing palette slots.
 
-Open design problem to address in the explainer + the ramp feature: a background-over-text effect (highlight/region/isearch/hl-line) must stay readable for EVERY foreground that can appear on it — i.e. the worst-case (lowest) contrast across the whole set of element fg colors, not a single pair. The usable background lightness is therefore capped by the darkest/closest fg in that set. See the discussion for the proposed approach + UX (limiting-fg readout, live contrast floor, worst-case mask on the picker).
+Open design problem to address in the explainer + the ramp feature: a background-over-text effect (highlight/region/isearch/hl-line) must stay readable for EVERY foreground that can appear on it — i.e. the worst-case (lowest) contrast across the whole set of element fg colors, not a single pair. The usable background lightness is therefore capped by the darkest/closest fg in that set.
+
+The v1 feature (ramp generation + background-contrast safety, with the worst-case-floor UX) is designed in [[file:docs/theme-studio-palette-ramps-spec.org][docs/theme-studio-palette-ramps-spec.org]]; build tasks come from spec-review of that spec. Harmonic fill (feature 2) stays vNext. This task is the explainer doc itself (=docs/design/theme-studio-color-harmony.org=, the methodology).
 
 ** TODO [#C] Internet radio now-playing song :feature:music:emms:
 Show the currently-playing song while streaming an internet radio station. Lives in =modules/music-config.el= (EMMS + MPV backend, M3U radio stations). The track title comes from the stream's ICY metadata — EMMS exposes it via =emms-track-description= / =emms-playing-time= and updates it on the metadata-change hook; MPV reports the ICY title too. Add an option to show the song in the minibuffer (e.g. echo on track change, or an on-demand command). Consider also a mode-line indicator as a second surface.