Preload system fonts on app startup

Cache font list in Rust via OnceLock, fire preload request from
main.ts so the font list is ready before user opens the picker.

desktop/src/lib.rs

@@ -5,6 +5,7 @@ use tauri::{
 
 use font_kit::source::SystemSource;
 use serde::Serialize;
+use std::sync::OnceLock;
 
 #[derive(Serialize, Clone)]
 struct FontFamily {
@@ -12,8 +13,9 @@ struct FontFamily {
     styles: Vec<String>,
 }
 
-#[tauri::command]
-fn list_system_fonts() -> Vec<FontFamily> {
+static FONT_CACHE: OnceLock<Vec<FontFamily>> = OnceLock::new();
+
+fn enumerate_system_fonts() -> Vec<FontFamily> {
     let source = SystemSource::new();
     let mut families: Vec<FontFamily> = Vec::new();
 
@@ -60,6 +62,11 @@ fn list_system_fonts() -> Vec<FontFamily> {
     families
 }
 
+#[tauri::command]
+fn list_system_fonts() -> Vec<FontFamily> {
+    FONT_CACHE.get_or_init(enumerate_system_fonts).clone()
+}
+
 #[tauri::command]
 fn load_system_font(family: String, style: String) -> Result<Vec<u8>, String> {
     let source = SystemSource::new();

src/engine/fonts.ts

@@ -13,15 +13,24 @@ function isTauri(): boolean {
   return typeof window !== 'undefined' && '__TAURI_INTERNALS__' in window
 }
 
+let tauriFontsPromise: Promise<TauriFontFamily[]> | null = null
+
 async function getTauriFonts(): Promise<TauriFontFamily[]> {
   if (tauriFontsCache) return tauriFontsCache
-  try {
-    const { invoke } = await import('@tauri-apps/api/core')
-    tauriFontsCache = await invoke<TauriFontFamily[]>('list_system_fonts')
-    return tauriFontsCache
-  } catch {
-    return []
+  if (!tauriFontsPromise) {
+    tauriFontsPromise = import('@tauri-apps/api/core')
+      .then(({ invoke }) => invoke<TauriFontFamily[]>('list_system_fonts'))
+      .then((fonts) => {
+        tauriFontsCache = fonts
+        return fonts
+      })
+      .catch(() => [])
   }
+  return tauriFontsPromise
+}
+
+export function preloadFonts(): void {
+  if (isTauri()) getTauriFonts()
 }
 
 export async function listFamilies(): Promise<string[]> {

src/main.ts

@@ -1,6 +1,9 @@
 import { createApp } from 'vue'
 
 import './app.css'
+import { preloadFonts } from '@/engine/fonts'
+
 import App from './App.vue'
 
+preloadFonts()
 createApp(App).mount('#app')