Chart fonts: self-hosted roster + document.fonts.load render gate

src/core/custom-theme.test.ts

@@ -3,6 +3,7 @@ import {
   CURRENT_THEME_VERSION,
   THEME_FONT_OPTIONS,
   applyFontToConfig,
+  collectFontFamilies,
   createCustomTheme,
 } from './custom-theme';
 import { THEME_PREVIEW_SPECS } from './theme-preview-specs';
@@ -62,13 +63,63 @@ describe('applyFontToConfig', () => {
   });
 });
 
+describe('collectFontFamilies', () => {
+  it('collects the top-level font and every *Font slot', () => {
+    const config = {
+      font: 'Inter',
+      axis: { labelFont: 'Spectral', titleFont: 'Spectral' },
+      legend: { labelFont: 'Caveat' },
+    };
+    expect(collectFontFamilies(config)).toEqual(new Set(['Inter', 'Spectral', 'Caveat']));
+  });
+
+  it('walks arrays (layered specs)', () => {
+    const spec = { layer: [{ mark: { font: 'A' } }, { mark: { font: 'B' } }] };
+    expect(collectFontFamilies(spec)).toEqual(new Set(['A', 'B']));
+  });
+
+  it('skips data and datasets (rows are never fonts)', () => {
+    const spec = {
+      data: { values: [{ font: 'NotAFont', x: 1 }] },
+      datasets: { d: [{ titleFont: 'AlsoNot' }] },
+      config: { font: 'Real' },
+    };
+    expect(collectFontFamilies(spec)).toEqual(new Set(['Real']));
+  });
+
+  it('ignores non-string font values', () => {
+    expect(collectFontFamilies({ font: 42, fontSize: 11 })).toEqual(new Set());
+  });
+
+  it('returns family stacks verbatim (the render gate loads them as-is)', () => {
+    expect(collectFontFamilies({ font: '"Inter", system-ui, sans-serif' })).toEqual(
+      new Set(['"Inter", system-ui, sans-serif']),
+    );
+  });
+
+  it('finds the font a theme applies (round-trip with applyFontToConfig)', () => {
+    const applied = applyFontToConfig({ axis: { labelFont: 'Old' } }, 'New');
+    expect(collectFontFamilies(applied)).toEqual(new Set(['New']));
+  });
+});
+
 describe('THEME_FONT_OPTIONS', () => {
   it('offers distinct, non-empty CSS stacks', () => {
     expect(THEME_FONT_OPTIONS.length).toBeGreaterThanOrEqual(4);
     const values = THEME_FONT_OPTIONS.map((f) => f.value);
+    const labels = THEME_FONT_OPTIONS.map((f) => f.label);
     expect(new Set(values).size).toBe(values.length);
+    expect(new Set(labels).size).toBe(labels.length);
     expect(values.every((v) => v.trim().length > 0)).toBe(true);
   });
+
+  it('every self-hosted family (quoted primary) carries a category fallback', () => {
+    // A quoted primary that hasn't loaded must degrade to a sensible system font,
+    // so each roster stack lists at least one fallback after the primary.
+    for (const { value } of THEME_FONT_OPTIONS.filter((o) => o.value.startsWith('"'))) {
+      expect(value).toContain(',');
+    }
+  });
 });
 
 describe('THEME_PREVIEW_SPECS', () => {