Keep c#, c++ and f# as the language of Markdown code blocks

[breken-ai]

Changes

• Markdown code blocks whose language ends in a symbol were highlighted as a different language. ```c# and ```c++ were highlighted with the C grammar and got data-language="c", and ```f# became f. Shiki registers c#, c++ and f# as aliases for csharp, cpp and fsharp, so these blocks now get the right grammar and data-language.
• The cause is the language- class pattern in highlightCodeBlocks (packages/markdown/remark/src/highlight.ts). It ended with \b, and there is no word boundary after a trailing # or +, so the match backtracked to c or f. The pattern no longer ends with \b. \S+ already stops at whitespace, so class strings with several classes still work.
• This only affects the remark processor. The Sätteri processor reads the language from data.lang or strips the language- prefix, so it already kept c#.
• With syntaxHighlight: 'prism', ```c++ and ```c# now go to Prism unchanged. Prism has no grammar under those names, so those blocks are left unhighlighted and Prism logs its usual "Unable to load the language" warning, the same as <Prism lang="c++" />. Before, they were highlighted with the C grammar.

Testing

• Added keeps symbols at the end of the code block language to packages/markdown/remark/test/highlight.test.ts. It renders ```c#, ```c++ and ```f# blocks and checks that each one keeps its language in data-language. It fails on main (data-language="c") and passes with this change. The whole @astrojs/markdown-remark suite passes (80/80), and tsc -b, Biome and Prettier are clean.

Docs

• No docs update needed. This is a bug fix for languages that Shiki already documents as supported.

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An AI agent (Breken, using Claude Code) found and fixed this bug, and the test above proves it.

🤖 Generated with Claude Code

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Latest commit: d891a2b

The changes in this PR will be included in the next version bump.

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Name	Type
@astrojs/markdown-remark	Patch

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