let handle;
onmessage=async({data})=>{
 try{
  if(data.action==='open'){
   const root=await navigator.storage.getDirectory();const dir=await root.getDirectoryHandle('cache',{create:true});const file=await dir.getFileHandle(data.key,{create:true});
   handle=await file.createSyncAccessHandle();handle.truncate(0);
  }else if(data.action==='write'){
   const bytes=new Uint8Array(data.buffer);let offset=0;while(offset<bytes.length){const wrote=handle.write(bytes.subarray(offset));if(!wrote)throw new Error('The browser cache write made no progress.');offset+=wrote;}
  }else if(data.action==='close'){
   handle?.flush();handle?.close();handle=null;
  }
  postMessage({ok:true});
 }catch(error){try{handle?.close();}catch{}handle=null;postMessage({error:error.message});}
};