fix: fall back to copy when OPFS move() throws on WebKit and retry failed worker downloads on the main thread

frontend/opfs-worker.js

@@ -76,12 +76,16 @@ self.onmessage = async (e) => {
       access.close();
     }
 
-    // Finalize: .part → permanent name. Prefer the native rename; fall back
+    // Finalize: .part → permanent name. Prefer the native rename, but treat
-    // to a chunked copy (still fully inside the worker, small fixed buffers).
+    // ANY move() failure as "unavailable" and fall back to a chunked copy —
+    // WebKit's move() has a different signature/behavior than Chrome's and
+    // throws TypeError ("Not enough arguments") rather than being absent.
     try { await dir.removeEntry(filename); } catch { /* no previous copy */ }
+    let renamed = false;
     if (typeof partHandle.move === 'function') {
-      await partHandle.move(filename);
+      try { await partHandle.move(filename); renamed = true; } catch { /* copy below */ }
-    } else {
+    }
+    if (!renamed) {
       const finalHandle = await dir.getFileHandle(filename, { create: true });
       const out = await finalHandle.createSyncAccessHandle();
       try {

frontend/opfs.js

@@ -154,18 +154,21 @@
             throw err;
           }
         } else {
-          // Fallback: buffer entirely (older browsers)
+          // No createWritable on this browser — main-thread OPFS writes are
-          const buf = await response.arrayBuffer();
+          // impossible (sync access handles are worker-only). Surface a real
-          const writable = await tmpHandle.createWritable();
+          // error instead of the old branch that called the missing API.
-          await writable.write(buf);
+          throw new Error('Offline saving is not supported in this browser');
-          await writable.close();
         }
 
         // Rename tmp → final. Prefer the native rename; else stream-copy so
         // the whole file is never buffered in main-thread memory at once.
+        // move() failures (WebKit's signature differs from Chrome's and
+        // throws TypeError) fall back to the copy path too.
+        let renamed = false;
         if (typeof tmpHandle.move === 'function') {
-          await tmpHandle.move(filename);
+          try { await tmpHandle.move(filename); renamed = true; } catch { /* copy below */ }
-        } else {
+        }
+        if (!renamed) {
           const finalHandle = await dir.getFileHandle(filename, { create: true });
           const finalWritable = await finalHandle.createWritable();
           const tmpFile = await tmpHandle.getFile();