Describe the bug
When using RustFS as an S3‑compatible backend, listing objects with a prefix that contains the same folder name twice in a row does not behave correctly.
If an object key contains folder1/folder2/..., everything works as expected, but if the path uses folder1/folder1/..., the nested prefix is not listed in either the RustFS UI or S3 clients such as s3cmd and mc.

This looks like a bug in how RustFS builds CommonPrefixes / handles prefixes for ListObjectsV2.

Environment

RustFS version: 1.0.0-alpha.72
Deployment: Docker Compose
S3 client: s3cmd, mc (and RustFS web UI)

Endpoint: https://rustfs....selfhosted.net (RustFS with TLS enabled)

To Reproduce

1. Create a bucket, for example:
   s3cmd mb s3://test-bucket

2. Upload two files with different nested prefixes:

# works fine
s3cmd put ./file1.txt s3://test-bucket/folder1/folder2/file1.txt

# problematic case
s3cmd put ./file2.txt s3://test-bucket/folder1/folder1/file2.txt

3. List the top‑level prefix:
   s3cmd ls s3://test-bucket/folder1/

4. Observe what is shown:

• s3cmd ls s3://test-bucket/folder1/
• RustFS web UI when you navigate into test-bucket → folder1/

Expected behavior
Both nested prefixes should be visible when listing folder1/:
folder1/folder2/
folder1/folder1/

In s3cmd:

s3cmd ls s3://test-bucket/folder1/

should show something like:

    DIR s3://test-bucket/folder1/folder1/

    DIR s3://test-bucket/folder1/folder2/

Actual behavior
For the folder1/folder2/file1.txt case everything works correctly:
s3cmd ls s3://test-bucket/folder1/ (and the UI) shows that folder2/ exists under folder1/.

For the folder1/folder1/file2.txt case:
s3cmd ls s3://test-bucket/folder1/
does not show that folder1/folder1/ exists.

The RustFS UI also does not show the nested folder1 under folder1/.
Direct access to the full key still works (as well as put, get, etc):

        s3cmd ls s3://test-bucket/folder1/folder1/
        s3cmd ls s3://test-bucket/folder1/folder1/file2.txt

so the object is stored, but the intermediate prefix is not returned in the listing.

It looks like a bug in how RustFS groups/returns prefixes for ListObjectsV2 when a subfolder has the same name as its parent (e.g. folder1/folder1/...).

Screenshots

Desktop:

• OS: MacOS Tahoe 26.1
• Browser: Firefox
• Version: 145.0.2 (aarch64)

Additional context

• The issue is reproducible both in the RustFS UI and via S3 clients (s3cmd, and mc) using standard Prefix=folder1/ + Delimiter=/ style listing.
• Other prefixes like folder1/folder2/... work fine, so the problem seems specific to repeated folder names in the path (X/X/...).
• In python boto3 it works fine (without an issue):

 % python3 s3_rustfs.py list                 

Objects in s3://test-bucket/
  folder1/folder1/file2.txt                                11 bytes   2025-12-10 14:17:47.285000+00:00
  folder1/folder2/file1.txt                                 8 bytes   2025-12-10 14:17:43.002000+00:00

Where s3_rustfs.py - simple script to put, get, list, etc. files from S3 buckets using boto3 library.

• Also UI shows the file if put prefix manually in URL, e.g. https://rustfs....selfhosted.net/rustfs/console/browser/test-bucket/folder1%2Ffolder1%2F