EDIT TEXT (text files only; images are immutable):
   PUT   https://skale.dev/throway/<id>   with new text body  -> replace whole content
   PATCH https://skale.dev/throway/<id>   with text body      -> append to content

Every upload/listing response includes an "editable" boolean per file, so an
agent can tell at a glance whether PUT/PATCH will work: true for text/* and
application/json, false for images and other binaries. A bundle or dir object
itself is editable:false; only its text/* or application/json files are.