fix(fonts): skip fontaine fallbacks

Author: harlan-zw

src/build/css/css-utils.ts

@@ -739,12 +739,22 @@ function isSystemFont(name: string): boolean {
   return name.startsWith('-') || name.startsWith('var(')
 }
 
+// fontaine/@nuxt/fonts emit metric-only fallback @font-face entries named
+// "<Family> fallback" (e.g. "Sofia Pro fallback") backed by local() Arial/Times.
+// They exist purely to reduce CLS in the browser and are not real downloadable
+// fonts, so OG renderers must not try to resolve them via fontless providers.
+const RE_FONTAINE_FALLBACK = / fallback$/i
+
+function isFontaineFallback(name: string): boolean {
+  return RE_FONTAINE_FALLBACK.test(name)
+}
+
 export function extractCustomFontFamilies(cssValue: string): string[] {
   return cssValue
     .replace(RE_IMPORTANT, '')
     .split(',')
     .map(p => p.trim().replace(RE_QUOTES, ''))
-    .filter(name => name && !GENERIC_FONT_FAMILIES.has(name.toLowerCase()) && !RE_ONLY_DIGITS.test(name) && !isSystemFont(name))
+    .filter(name => name && !GENERIC_FONT_FAMILIES.has(name.toLowerCase()) && !RE_ONLY_DIGITS.test(name) && !isSystemFont(name) && !isFontaineFallback(name))
 }
 
 // ============================================================================

src/build/fontless.ts

@@ -626,13 +626,17 @@ export async function resolveOgImageFonts(options: {
     const coveredFamilies = new Set(allFonts.map(f => f.family))
     let missingFamilies: string[] = []
 
+    // Skip fontaine-generated metric fallbacks ("<Family> fallback") — they're
+    // local() metric shims for CLS, not real downloadable fonts.
+    const isFontaineFallback = (name: string): boolean => / fallback$/i.test(name)
+
     if (fontRequirements.families.length > 0) {
-      missingFamilies = fontRequirements.families.filter(f => !coveredFamilies.has(f))
+      missingFamilies = fontRequirements.families.filter(f => !coveredFamilies.has(f) && !isFontaineFallback(f))
     }
     else {
       const defaultVar = tw4FontVars['font-sans']
       if (defaultVar)
-        missingFamilies = extractCustomFontFamilies(defaultVar).filter(f => !coveredFamilies.has(f))
+        missingFamilies = extractCustomFontFamilies(defaultVar).filter(f => !coveredFamilies.has(f) && !isFontaineFallback(f))
     }
 
     if (missingFamilies.length > 0) {