Inconsistent behavior when uploading to external storage root vs sub directory

How to use GitHub

• Please use the 👍 reaction to show that you are affected by the same issue.
• Please don't comment if you have no relevant information to add. It's just extra noise for everyone subscribed to this issue.
• Subscribe to receive notifications on status change and new comments.

Steps to reproduce

Preparation (one time)

1. Configure a file access rule to block uploads above 5 Mb
2. Ensure that chunked upload is enabled: occ config:app:delete files max_chunk_size
3. Add an external S3 storage.
4. Create a sub directory inside the external storage.

Case 1 (correct)

1. Upload a big file directly to the external storage's root folder.
2. Observe that the upload is blocked after all chunks were uploaded (error on assembly).

Case 2 (broken)

1. Upload a big file to the sub directory inside the external store.
2. Observe that the upload is blocked immediately when starting the first chunk.

Expected behavior

Case 1 is behaving as expected. Case 2 is not behaving as expected. The upload should be blocked after assembly in both cases.

Actual behavior

The upload is blocked immediately in case 2 instead of postponing the check until the whole file is available like in case 1.

Server configuration

Web server: Apache (Content-Length fix is applied)

PHP version: 8.1

Nextcloud version: master

Reproduce both cases with chunked uploads, the 5 MB access rule, and an external S3 storage, using the documented occ configuration command. Trace how access control handles uploads at the external-storage root versus a subdirectory and how chunk assembly is reached. Done means both paths defer the size check until assembly, with regression coverage for the difference.