Uploading without folder_id answered `500 Internal Error: folder_id is
required to determine file owner`. A missing required field is the
caller's error; as an internal_error it produced `error_type: Internal
Error`, which the SPA cannot distinguish from the server breaking — so a
malformed request looked like an outage.
Both sites become validation_error (ErrorKind::InvalidInput → 400), with
messages that say WHY the field is needed rather than restating that it
is: the destination folder determines the file's owner and drive.
The OpenAPI request body described it as "optional folder_id field",
which is how it came to be omitted — hit while writing
thumbnail_etag_content_keyed.hurl, where the upload was written from the
documented contract and 500'd. Now stated as required.
Regression test asserts the status AND that error_type is not "Internal
Error", since the contract the SPA switches on is error_type rather than
the message.
Edouard Vanbelle
d7de1c41e7