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
-    // to a chunked copy (still fully inside the worker, small fixed buffers).
+    // Finalize: .part → permanent name. Prefer the native rename, but treat
+    // 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);
-    } else {
+      try { await partHandle.move(filename); renamed = true; } catch { /* copy below */ }
+    }
+    if (!renamed) {
       const finalHandle = await dir.getFileHandle(filename, { create: true });
       const out = await finalHandle.createSyncAccessHandle();
       try {