## Summary
Fixes [#15585](https://github.com/infiniflow/ragflow/issues/15585).
- Route markdown preview through the shared `request` client (same as
txt/image previewers) so `Authorization` headers and interceptors are
applied consistently.
- Add a unit test covering `AUTH_BETA` token loading for embedded search
auth.
## Root cause
Search result preview for `.md`/`.mdx` used raw `fetch`, which did not
apply the same auth path as other preview types. That led to `401` on
`GET /api/v1/documents/{id}/preview` even when the user was logged in or
using an embedded search `auth` query param.
## Test plan
- [ ] Log in, run a search, open a markdown citation link — preview
loads (no 401).
- [ ] Open an embedded shared search URL with `auth` query param,
preview a markdown file — preview loads.
- [ ] Confirm PDF/txt preview still works in the same search UI.
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Co-authored-by: MkDev11 <89318445+bitloi@users.noreply.github.com>
Co-authored-by: Wang Qi <wangq8@outlook.com>
### What problem does this PR solve?
LLM/chat and search UIs render Markdown in several places (document
preview, floating chat widget, next-search, etc.). Plugin lists and
behavior were duplicated or inconsistent, and single newlines in model
output were not always rendered as visible line breaks, which hurts
readability for chat-style content.
This PR centralizes shared **remark/rehype** configuration (including
**`remark-breaks`** for newline handling) and wires the main Markdown
surfaces to use it, so behavior is consistent and easier to maintain.
### Type of change
- [x] Refactoring
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Co-authored-by: Yingfeng Zhang <yingfeng.zhang@gmail.com>
