Issue Summary

Hangul characters is not getting rendered properly in confluence when a .txt file is attached. The text shows as rectangle boxes in the preview.

Steps to Reproduce

1. Create a UTF-8 encoded text file containing Korean characters, e.g.:

   테스트2

   Save it as KoreanTest2.txt with UTF-8 encoding.

2. In Confluence, attach this .txt file to a page (via drag-and-drop or Attachments).
3. On the page, click the attachment to open the preview (thumbnail/HD view).
4. In the browser Developer Tools → Network tab, observe the calls to the document conversion REST API:
   • GET /rest/documentConversion/latest/conversion/convertThumbnail/{attachmentId}/{version}
   • GET /rest/documentConversion/latest/conversion/convertHD/{attachmentId}/{version}
5. Result:
   • The Document Conversion Sandbox receives and processes the request 
   • However, the convertHD (and/or thumbnail) REST request returns HTTP 415 Unsupported Media Type for this .txt attachment.
   • The preview UI fails (or shows broken text)

Expected Results

Preview should display fine

Actual Results

• The preview UI fails (or shows broken text)
• 

Workaround

Currently there is no known workaround for this behavior. A workaround will be added here when available