feat(markdown): support embedding YouTube and Kaltura videos via link-interception

[rschlaefli]

Description

Supports embedding videos from controlled sources (YouTube and UZH Kaltura/SWITCHcast) in Markdown fields by intercepting links labeled as video or embed.

For Kaltura, we use the SWITCHcast PlaykitJs embed endpoint to bypass the frame-based login loop entirely.

This implementation has been fully audited using droid running GLM 5.2 for security, accessibility (WCAG), type safety, and property-forwarding correctness.

Proposed Changes

• packages/markdown/src/VideoEmbed.tsx:
  • Implements safe parsing helpers with strict value validation (getYoutubeId, getKalturaId, getKalturaPartnerId, getKalturaUiConfId).
  • Added strict domain validation for Kaltura (kaltura.com, *.kaltura.com, cast.switch.ch, *.cast.switch.ch) and strict character set validation for YouTube IDs (^[a-zA-Z0-9_-]{11}$).
  • Created the VideoEmbed React component rendering a responsive iframe with a screen-reader title and performance-optimizing loading="lazy".
• packages/markdown/src/Markdown.tsx:
  • Modified the custom a anchor renderer in rehypeReact to render the embedded player when matching video URLs are encountered.
  • Trimmed label text to support varied formatting of link text like [video ](url).
  • Safely forwarded all standard anchor tag attributes (target, rel, ...rest) to preserve existing link-processing configurations like rehype-external-links.

Manual Verification / How to Test

1. Embed a YouTube video using [video](https://www.youtube.com/watch?v=dQw4w9WgXcQ). It should render a responsive player wrapper with the YouTube iframe.
2. Embed a Kaltura video using the hosted portal URL layout [video](https://uzh.mediaspace.cast.switch.ch/media/10+Untersuchung+Kopf+beim+Hund/0_ipqc15ga/124135). It should resolve the entryId and successfully render the Kaltura playkit login-bypass player iframe.
3. Embed a Kaltura video using the raw embed code iframe URL [video](https://uzh.mediaspace.cast.switch.ch/embed/secure/iframe/entryId/0_um01ms1s/uiConfId/23449004/st/0). It should preserve the correct uiConfId and render the playkit player.
4. Ensure other link configurations, e.g., [Link to YouTube](https://www.youtube.com/watch?v=dQw4w9WgXcQ), continue to render as regular hyperlinks with original properties (e.g. target="_blank").

[coderabbitai]

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[greptile-apps]

Confidence Score: 4/5

This is close, but the remaining host check should be fixed before merging.

• Regular links now keep their forwarded anchor attributes.
• Kaltura lookalike hosts are rejected by the updated boundary checks.
• The youtu.be check still accepts a lookalike domain and can turn that labeled link into an embed.

packages/markdown/src/VideoEmbed.tsx

Security Review

A remaining YouTube short-link host check can still accept lookalike domains ending in youtu.be.

Important Files Changed

Filename	Overview
packages/markdown/src/VideoEmbed.tsx	Adds video parsing helpers and iframe rendering, with one remaining short-domain host validation issue.
packages/markdown/src/Markdown.tsx	Adds video link interception and preserves anchor props for regular links.
packages/markdown/test/VideoEmbed.test.ts	Adds parser coverage for accepted video URLs and several rejected URL shapes.
packages/markdown/package.json	Adds Vitest and a package test script.

_{Reviews (10): Last reviewed commit: "test(markdown): add unit tests for Video..." | Re-trigger Greptile}

[gitguardian]

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[greptile-apps]

Short Host Bypass

host.endsWith('youtu.be') still accepts lookalike registrable domains such as attackyoutu.be. A labeled link like [video](https://attackyoutu.be/dQw4w9WgXcQ) passes this branch, extracts the path as a video id, and renders an embed even though the source link was not from youtu.be or one of its subdomains. Require the same exact-host or dot-boundary check used for the other allowed hosts.