Uploaded data shouldn't be sent to Quirrel, but be stored in your own database. Add a new DB entity for it:
Then when a user uploads something, you insert it into the database and enqueue the resulting record's ID into Quirrel.
Our Quirrel Queue then fetches the corresponding data from the database and does the required processing. After that's done, it deletes the database record (alternative: add a flag called "finishedProcessing" and set it to true).
Now when you want to know whether an upload has already been processed, you can look it up in your own database: