[codex] Add content-rich link preview images

[tin-computer]

Summary

This changes pasted with.md share links from a generic brand preview image to a generated preview image that shows the shared document title and a compact excerpt from the markdown content.

What changed

• Added dynamic 1200x630 PNG preview routes for anonymous shares at /og/s/[shareId] and repository shares at /og/r/[token].
• Updated /s/[shareId] and /r/[token] metadata so Open Graph and Twitter previews use the share-specific title, description, and image route.
• Added markdown cleanup helpers that strip frontmatter, heading markers, links, images, lists, table separators, code fences, and other markdown noise before building preview text.
• Kept share pages non-indexable and added X-Robots-Tag: noindex, nofollow, noarchive to the generated image responses.

Why

When people paste a with.md link today, the preview image is the same static /with-md.jpg everywhere. That makes share links feel generic and hides the document context. The new preview shows the actual title and enough content to make the link recognizable before someone opens it.

Validation

• npm --workspace web run test -- link-preview
• npm --workspace web run test
• npm --workspace web run build
• Local built-app smoke check against /og/s/test-preview and /og/r/test-preview: both returned 200 OK, content-type: image/png, x-robots-tag: noindex, nofollow, noarchive, and 1200x630 PNG output.

Notes

• The preview image routes use Edge runtime because next/og builds cleanly that way in this app.
• The repository-share token hash is computed with Web Crypto in the preview helper so the Edge route does not import Node crypto.

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Project	Deployment	Actions	Updated (UTC)
with-md-web	Ready	Preview, Comment	Jun 12, 2026 4:49am