Markdown preview doesn't render callouts / GitHub-style alerts (> [!note])

Summary

The built-in Markdown preview renders Obsidian/GitHub callout (alert) blockquotes as plain blockquotes. A block like > [!note] shows the literal [!note] marker instead of a styled callout. This makes notes authored in Obsidian (which relies heavily on callouts) hard to read inside Orca.

Steps to reproduce

Open a .md file containing:

> [!note] Optional title
> Body text of the callout.

> [!warning]
> Another one.

Expected: styled callout boxes (icon + colored border/title), marker line consumed.
Actual: ordinary blockquotes; the [!note] / [!warning] text is shown verbatim.

Root cause (from inspecting the shipped renderer bundle, v1.4.137)

The preview's react-markdown pipeline is:

• remark: remark-parse, remark-gfm, remark-frontmatter, remark-breaks, remark-math, plus the custom wikilink plugin
• rehype: rehype-raw, rehype-sanitize (with defaultSchema), rehype-slug, rehype-highlight, rehype-katex

remark-gfm does not implement alert/callout blockquotes — those need a dedicated plugin. There's currently no alert/callout plugin in the chain, so > [!type] falls through as a blockquote.

Proposed fix

Add one plugin to the existing pipeline:

• Minimal (GitHub alert subset — NOTE/TIP/IMPORTANT/WARNING/CAUTION): add remark-github-blockquote-alert to remarkPlugins (it ships matching CSS).
• Fuller (Obsidian superset — arbitrary types, inline title on the marker line, foldable [!note]- / [!note]+): a small remark/rehype transform that rewrites a blockquote whose first paragraph starts with /^\[!(\w+)\]([+-]?)\s?(.*)/ into a div.callout.callout-<type>.

Implementation note (gotcha)

Because the pipeline runs rehype-sanitize with defaultSchema, the added callout div / className will be stripped unless you either (a) run the transform after sanitize, or (b) extend the sanitize schema to allow the callout element + class names. Worth accounting for so the styling doesn't silently disappear.

Environment

Orca 1.4.137, macOS (Apple Silicon).