fix(fetch): use Vite proxy + Vercel rewrites for reliable Dropbox loading

Replace unreliable third-party CORS proxies (allorigins, cors-anywhere,
thingproxy) with a local /dropbox-file route proxied server-side:
- vite.config.ts: add dev server proxy for /dropbox-file -> dl.dropboxusercontent.com
- vercel.json: add rewrite rule for the same route in production
- App.tsx: simplify fetch logic to use single reliable proxy path

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/App.tsx

@@ -25,34 +25,23 @@ export default function App() {
 
   useEffect(() => {
     const loadDefaultData = async () => {
-      // Use different proxies as fallbacks
+      // Use Vite's dev proxy to avoid CORS issues
-      const proxies = [
+      const fileUrl = '/dropbox-file/scl/fi/nkyabkq2jdwfudof2ovrl/Data-Matrix.xlsx?rlkey=1cz5fuabwipqqivihii7sybw0&st=io0g4wvb&dl=1';
-        (url: string) => `https://api.allorigins.win/raw?url=${encodeURIComponent(url)}`,
-        (url: string) => `https://cors-anywhere.herokuapp.com/${url}`, // Often needs manual activation but we'll try
-        (url: string) => `https://thingproxy.freeboard.io/fetch/${url}`
-      ];
-
-      const dropboxUrl = 'https://dl.dropboxusercontent.com/scl/fi/nkyabkq2jdwfudof2ovrl/Data-Matrix.xlsx?rlkey=1cz5fuabwipqqivihii7sybw0&st=io0g4wvb&dl=1';
 
       setIsLoadingDefault(true);
       setDefaultLoadError(null);
 
-      let lastError = null;
-
-      for (const getProxyUrl of proxies) {
       try {
-          const proxyUrl = getProxyUrl(dropboxUrl);
+        console.log('Fetching Data-Matrix.xlsx via Vite proxy...');
-          console.log(`Attempting to fetch via: ${proxyUrl}`);
+        const response = await fetch(fileUrl);
-          
-          const response = await fetch(proxyUrl);
 
         if (!response.ok) {
-            throw new Error(`Proxy returned status ${response.status}: ${response.statusText}`);
+          throw new Error(`HTTP ${response.status}: ${response.statusText}`);
         }
 
         const arrayBuffer = await response.arrayBuffer();
         if (arrayBuffer.byteLength < 100) {
-              throw new Error("File too small, possibly empty or error page");
+          throw new Error('File too small — possibly empty or error response');
         }
 
         const wb = XLSX.read(arrayBuffer, { type: 'array' });
@@ -64,8 +53,7 @@ export default function App() {
           const rawHeaders = data[0];
           const rawRows = data.slice(1);
 
-            // Apply Supabase overrides
+          console.log('Applying Supabase overrides...');
-            console.log("Applying Supabase overrides...");
           const syncedData = await getAllSyncedRows();
           const articleNoIdx = COLUMNS.ARTICLE_NO;
 
@@ -82,18 +70,13 @@ export default function App() {
             hasUnsavedChanges: false
           });
           setActiveModule('descriptions');
-            setIsLoadingDefault(false);
-            return; // Success!
         }
       } catch (err) {
-          console.error(`Failed with proxy:`, err);
+        console.error('Failed to load from Dropbox:', err);
-          lastError = err;
+        setDefaultLoadError(err instanceof Error ? err.message : 'Connection failed');
-        }
+      } finally {
-      }
-
-      // If we reach here, all proxies failed
-      setDefaultLoadError(lastError instanceof Error ? lastError.message : 'All connection attempts failed');
         setIsLoadingDefault(false);
+      }
     };
 
     loadDefaultData();

vercel.json

@@ -0,0 +1,8 @@
+{
+  "rewrites": [
+    {
+      "source": "/dropbox-file/:path*",
+      "destination": "https://dl.dropboxusercontent.com/:path*"
+    }
+  ]
+}

vite.config.ts

@@ -17,8 +17,15 @@ export default defineConfig(({mode}) => {
     },
     server: {
       // HMR is disabled in AI Studio via DISABLE_HMR env var.
-      // Do not modify—file watching is disabled to prevent flickering during agent edits.
+      // Do not modify - file watching is disabled to prevent flickering during agent edits.
       hmr: process.env.DISABLE_HMR !== 'true',
+      proxy: {
+        '/dropbox-file': {
+          target: 'https://dl.dropboxusercontent.com',
+          changeOrigin: true,
+          rewrite: (path) => path.replace(/^\/dropbox-file/, ''),
+        },
+      },
     },
   };
 });