feat(theme-studio): add the color-families model core

Four pure functions in app-core.js, all derived from the hex so renaming never moves a color. familiesFromPalette groups a flat palette into the ground strip (the bg/fg assignment hexes, pinned, de-duped) plus hue families: near-neutrals split off by a chroma threshold, the rest cluster by hue proximity with a 25-degree gap and a 360 wrap, each family's base its most-saturated member. regenFamily returns a family's symmetric ramp around the base (n=0 is the base alone, handled without ramp()'s 1-4 clamp). rankByLightness gives each current member a signed offset from the base, and stepRepointPlan maps old positions to new ones across a regenerate, listing the positions that drop out so the caller can leave their references a visible "(gone)".

Phase 1 of the color-families spec, pure logic, no UI. 13 node tests cover the gap split/merge, neutrals, absent and de-duped ground hexes, n=0, lightness ranking, and the survivor/removed repoint split. Suite 78 to 91 green.

1 files changed, 113 insertions, 0 deletions

diff --git a/scripts/theme-studio/test-families.mjs b/scripts/theme-studio/test-families.mjs
new file mode 100644
index 000000000..071c8307f
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+++ b/scripts/theme-studio/test-families.mjs
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+// Unit tests for the color-families model (app-core.js): grouping a flat palette
+// into hue families, regenerating a family's ramp, ranking members by lightness,
+// and planning the assignment re-point across a regenerate. Phase 1 of the
+// color-families spec. Pure, no DOM. Run: node --test scripts/theme-studio/
+
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { familiesFromPalette, regenFamily, rankByLightness, stepRepointPlan } from './app-core.js';
+import { oklch2hex } from './colormath.js';
+
+// Build a palette entry at a controlled OKLCH hue so clustering is deterministic.
+const at = (L, C, H, name) => [oklch2hex(L, C, H).hex, name || ('c' + H)];
+
+// --- familiesFromPalette ----------------------------------------------------
+
+test('familiesFromPalette: Normal — separated hues split into one family each', () => {
+  const pal = [at(0.6, 0.1, 30, 'red'), at(0.6, 0.1, 150, 'green'), at(0.6, 0.1, 270, 'blue')];
+  const { ground, families } = familiesFromPalette(pal, { bg: '#000000', fg: '#ffffff' });
+  assert.equal(families.length, 3, 'three separated hues -> three families');
+  assert.equal(ground.length, 2, 'ground strip carries bg and fg');
+  for (const f of families) assert.equal(f.members.length, 1);
+});
+
+test('familiesFromPalette: Boundary — hues within the gap stay one family', () => {
+  const pal = [at(0.55, 0.1, 250, 'b1'), at(0.6, 0.1, 256, 'b2')]; // 6° apart < 25°
+  const { families } = familiesFromPalette(pal, { bg: '#000000', fg: '#ffffff' });
+  assert.equal(families.length, 1, 'a near hue-pair is one family');
+  assert.equal(families[0].members.length, 2);
+});
+
+test('familiesFromPalette: Boundary — hues past the gap split', () => {
+  const pal = [at(0.6, 0.1, 250, 'b'), at(0.6, 0.1, 200, 'c')]; // 50° apart > 25°
+  const { families } = familiesFromPalette(pal, { bg: '#000000', fg: '#ffffff' });
+  assert.equal(families.length, 2);
+});
+
+test('familiesFromPalette: Boundary — near-neutral colors form a separate family', () => {
+  const pal = [at(0.6, 0.1, 250, 'blue'), at(0.5, 0.004, 250, 'gray')]; // gray below the chroma threshold
+  const { families } = familiesFromPalette(pal, { bg: '#000000', fg: '#ffffff' });
+  const neutral = families.find(f => f.neutral);
+  assert.ok(neutral, 'a neutral family exists');
+  assert.ok(neutral.members.some(m => m.name === 'gray'));
+  assert.ok(families.some(f => !f.neutral && f.members.some(m => m.name === 'blue')));
+});
+
+test('familiesFromPalette: Boundary — ground hex absent from the palette still forms the strip', () => {
+  const pal = [at(0.6, 0.1, 250, 'blue')];
+  const { ground } = familiesFromPalette(pal, { bg: '#0d0b0a', fg: '#f0fef0' });
+  assert.equal(ground.length, 2);
+  assert.ok(ground.some(g => g.hex.toLowerCase() === '#0d0b0a' && g.role === 'bg'));
+  assert.ok(ground.some(g => g.role === 'fg'));
+});
+
+test('familiesFromPalette: Boundary — a chip at a ground hex is not duplicated into a family', () => {
+  const pal = [['#0d0b0a', 'ground'], at(0.6, 0.1, 250, 'blue')];
+  const { ground, families } = familiesFromPalette(pal, { bg: '#0d0b0a', fg: '#f0fef0' });
+  assert.ok(ground.some(g => g.hex.toLowerCase() === '#0d0b0a'));
+  assert.ok(!families.some(f => f.members.some(m => m.hex.toLowerCase() === '#0d0b0a')), 'ground chip stays out of families');
+});
+
+// --- regenFamily ------------------------------------------------------------
+
+test('regenFamily: Normal — n steps each side plus the base, ordered by offset', () => {
+  const r = regenFamily('#67809c', 2);
+  assert.equal(r.members.length, 5);
+  assert.deepEqual(r.members.map(m => m.offset), [-2, -1, 0, 1, 2]);
+  assert.equal(r.members.find(m => m.offset === 0).hex, '#67809c');
+});
+
+test('regenFamily: Boundary — n=0 is the base alone, no ramp() clamp to 1', () => {
+  const r = regenFamily('#67809c', 0);
+  assert.deepEqual(r.members, [{ hex: '#67809c', offset: 0, clamped: false }]);
+});
+
+test('regenFamily: Error — a malformed base returns a structured bad-hex', () => {
+  assert.deepEqual(regenFamily('nope', 2), { members: [], error: 'bad-hex' });
+});
+
+// --- rankByLightness --------------------------------------------------------
+
+test('rankByLightness: Normal — offsets are signed distance from the base by lightness', () => {
+  const members = regenFamily('#67809c', 2).members.map(m => m.hex);
+  const ranked = rankByLightness(members, '#67809c');
+  const base = ranked.find(m => m.hex === '#67809c');
+  assert.equal(base.offset, 0);
+  const sorted = [...ranked].sort((a, b) => a.offset - b.offset);
+  assert.deepEqual(sorted.map(m => m.offset), [-2, -1, 0, 1, 2]);
+});
+
+test('rankByLightness: Boundary — a base not among the members ranks by nearest lightness', () => {
+  const members = ['#222222', '#888888', '#dddddd'];
+  const ranked = rankByLightness(members, '#8a8a8a'); // near the mid member
+  const mid = ranked.find(m => m.hex === '#888888');
+  assert.equal(mid.offset, 0, 'nearest-lightness member is the base rank');
+});
+
+// --- stepRepointPlan --------------------------------------------------------
+
+test('stepRepointPlan: Normal — surviving offsets map old->new, changed hex only', () => {
+  const oldR = [{ hex: '#111111', offset: -1 }, { hex: '#222222', offset: 0 }, { hex: '#333333', offset: 1 }];
+  const neu = [{ hex: '#111111', offset: -1 }, { hex: '#aaaaaa', offset: 0 }, { hex: '#444444', offset: 1 }];
+  const { map, removed } = stepRepointPlan(oldR, neu);
+  assert.deepEqual(removed, []);
+  assert.deepEqual(map, [['#222222', '#aaaaaa'], ['#333333', '#444444']]); // -1 unchanged, skipped
+});
+
+test('stepRepointPlan: Boundary — an offset with no new counterpart is removed, not repointed', () => {
+  const oldR = [{ hex: '#000033', offset: -3 }, { hex: '#222222', offset: 0 }];
+  const neu = [{ hex: '#222222', offset: 0 }]; // count dropped, -3 gone
+  const { map, removed } = stepRepointPlan(oldR, neu);
+  assert.deepEqual(map, []);
+  assert.deepEqual(removed, ['#000033']);
+});