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

@@ -25,75 +25,58 @@ export default function App() {
 
   useEffect(() => {
     const loadDefaultData = async () => {
-      // Use different proxies as fallbacks
-      const proxies = [
-        (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';
+      // Use Vite's dev proxy to avoid CORS issues
+      const fileUrl = '/dropbox-file/scl/fi/nkyabkq2jdwfudof2ovrl/Data-Matrix.xlsx?rlkey=1cz5fuabwipqqivihii7sybw0&st=io0g4wvb&dl=1';
 
       setIsLoadingDefault(true);
       setDefaultLoadError(null);
 
-      let lastError = null;
+      try {
+        console.log('Fetching Data-Matrix.xlsx via Vite proxy...');
+        const response = await fetch(fileUrl);
 
-      for (const getProxyUrl of proxies) {
-        try {
-          const proxyUrl = getProxyUrl(dropboxUrl);
-          console.log(`Attempting to fetch via: ${proxyUrl}`);
-          
-          const response = await fetch(proxyUrl);
-          
-          if (!response.ok) {
-            throw new Error(`Proxy returned status ${response.status}: ${response.statusText}`);
-          }
-          
-          const arrayBuffer = await response.arrayBuffer();
-          if (arrayBuffer.byteLength < 100) {
-              throw new Error("File too small, possibly empty or error page");
-          }
-
-          const wb = XLSX.read(arrayBuffer, { type: 'array' });
-          const wsname = wb.SheetNames[0];
-          const ws = wb.Sheets[wsname];
-          const data = XLSX.utils.sheet_to_json<any[]>(ws, { header: 1 });
-          
-          if (data.length > 0) {
-            const rawHeaders = data[0];
-            const rawRows = data.slice(1);
-            
-            // Apply Supabase overrides
-            console.log("Applying Supabase overrides...");
-            const syncedData = await getAllSyncedRows();
-            const articleNoIdx = COLUMNS.ARTICLE_NO;
-            
-            const processedRows = rawRows.map(row => {
-              const articleNo = String(row[articleNoIdx]);
-              return syncedData[articleNo] || row;
-            });
-
-            setAppState({
-              headers: rawHeaders,
-              data: processedRows,
-              fileName: 'Data-Matrix.xlsx (Cloud Sync)',
-              fileDate: new Date(),
-              hasUnsavedChanges: false
-            });
-            setActiveModule('descriptions');
-            setIsLoadingDefault(false);
-            return; // Success!
-          }
-        } catch (err) {
-          console.error(`Failed with proxy:`, err);
-          lastError = err;
+        if (!response.ok) {
+          throw new Error(`HTTP ${response.status}: ${response.statusText}`);
         }
-      }
 
-      // If we reach here, all proxies failed
-      setDefaultLoadError(lastError instanceof Error ? lastError.message : 'All connection attempts failed');
-      setIsLoadingDefault(false);
+        const arrayBuffer = await response.arrayBuffer();
+        if (arrayBuffer.byteLength < 100) {
+          throw new Error('File too small — possibly empty or error response');
+        }
+
+        const wb = XLSX.read(arrayBuffer, { type: 'array' });
+        const wsname = wb.SheetNames[0];
+        const ws = wb.Sheets[wsname];
+        const data = XLSX.utils.sheet_to_json<any[]>(ws, { header: 1 });
+
+        if (data.length > 0) {
+          const rawHeaders = data[0];
+          const rawRows = data.slice(1);
+
+          console.log('Applying Supabase overrides...');
+          const syncedData = await getAllSyncedRows();
+          const articleNoIdx = COLUMNS.ARTICLE_NO;
+
+          const processedRows = rawRows.map(row => {
+            const articleNo = String(row[articleNoIdx]);
+            return syncedData[articleNo] || row;
+          });
+
+          setAppState({
+            headers: rawHeaders,
+            data: processedRows,
+            fileName: 'Data-Matrix.xlsx (Cloud Sync)',
+            fileDate: new Date(),
+            hasUnsavedChanges: false
+          });
+          setActiveModule('descriptions');
+        }
+      } catch (err) {
+        console.error('Failed to load from Dropbox:', err);
+        setDefaultLoadError(err instanceof Error ? err.message : 'Connection failed');
+      } finally {
+        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/, ''),
+        },
+      },
     },
   };
 });