Fonts: carry uploaded faces through export/import + embed in SVG export

src/app/services/chart-renderer.ts

@@ -11,6 +11,8 @@ import vegaEmbed, { type Result as EmbedResult } from 'vega-embed';
 import type { VisualizationSpec } from 'vega-embed';
 import type { Config } from 'vega-lite';
 import { collectFontFamilies } from '@core/custom-theme';
+import { embedFontsInSvg } from '@core/chart-export';
+import type { FontAsset } from '@core/font-asset';
 
 /** Options for `RenderHandle.toImageURL` (spec §08 → Per-chart export). */
 interface ImageExportOptions {
@@ -31,6 +33,14 @@ interface ImageExportOptions {
    * it transparent. Default `null`.
    */
   background?: string | null;
+  /**
+   * Uploaded font faces the chart references, embedded into the **SVG** as base64
+   * `@font-face` rules so it renders the right type off-app (spec §08; scope doc
+   * §4). Ignored for PNG (the raster already bakes in the glyphs). Omitted/empty
+   * leaves only the family name, which falls back to a system font elsewhere. The
+   * caller (which holds the font library) resolves which faces are referenced.
+   */
+  embedFonts?: ReadonlyArray<FontAsset>;
 }
 
 export interface RenderHandle {
@@ -231,12 +241,15 @@ export async function renderSpec(
       node.replaceChildren();
     },
     async toImageURL(format, options = {}) {
-      const { scale = 1, background = null } = options;
+      const { scale = 1, background = null, embedFonts = [] } = options;
       if (format === 'svg') {
-        // Vector — resolution-independent, so dpr/scale don't apply. A background
-        // is added as a full-bleed rect rather than baked into the live view.
-        const svg = await result.view.toSVG();
-        return svgDataUrl(background ? withSvgBackground(svg, background) : svg);
+        // Vector — resolution-independent, so dpr/scale don't apply. The view
+        // writes only family names, so referenced uploaded faces are embedded as
+        // @font-face data-URIs; a background is added as a full-bleed rect. Both
+        // are injected into the serialized string, not the live view.
+        let svg = embedFontsInSvg(await result.view.toSVG(), embedFonts);
+        if (background) svg = withSvgBackground(svg, background);
+        return svgDataUrl(svg);
       }
       // Multiply the requested scale by the device pixel ratio so a "1×" export is
       // as crisp as the chart on screen (the Retina fix — see ImageExportOptions).