Instead of regex-parsing markdown content to find attachment URLs
(fragile), the frontend now tracks uploaded attachment IDs and sends
them with the comment creation request. The backend links them by ID.
Frontend: upload returns attachment ID, comment/reply inputs collect
IDs during editing session, pass as attachment_ids on submit.
Backend: CreateComment accepts attachment_ids, links by ID+issue scope.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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