[harlan-zw]

Stacked on #241.

❓ Type of change

• ✨ New feature

📚 Description

#241 stopped SKILL.md from loading images off non-GitHub hosts, which turned every shields.io badge into a plain link. Avatars were still hotlinked from GitHub, X, and Bluesky on about 30 surfaces, and GitHub itself still saw every visitor who opened a skill with a raw image.

Now every third-party image loads from /_img on skilld.dev. Avatar hosts go through a strict allowlist; SKILL.md images carry an HMAC signature, so the route cannot be used as an open proxy. Upstream sees a generic user agent and nothing from the visitor. The site also sends Referrer-Policy: strict-origin-when-cross-origin.

📝 Migration

Set the signing secret before deploying:

openssl rand -base64 32 | npx wrangler secret put NUXT_IMAGE_PROXY_KEY

If the secret is missing, SKILL.md images fall back to links and an image-proxy-key warning is logged. Avatars keep working, since they need no key.

Open questions:

• The render stored at sync time still uses links, because a signature there would tie D1 rows to one key. Request-time renders re-sign from rendered_raw, so this only shows for legacy rows with no raw copy.
• raw.githubusercontent.com serves SVG as text/plain, so an SVG committed to a repo returns 415 through the proxy. It did not render as a direct <img> either, but sniffing SVG by extension would fix it if we want that.
• OG image props still take absolute GitHub avatar URLs. Those render server side and never touch a visitor.

🤖 AI disclosure: Harlan Agent Kit modified this description. My AI open-source policy.

[harlan-zw]

Checked by hand in nuxi dev and a wrangler dev build, since CI cannot cover it:

• Home page, scrolled end to end: 68 image requests, none to a third-party host, every avatar served from /_img/avatar
• A skill page with two shields.io badges added to its local SKILL.md: both render inline from /_img/signed, with referrerpolicy="no-referrer"
• A signed SVG response carries default-src 'none'; style-src 'unsafe-inline'; sandbox and nosniff; a tampered signature, a non-avatar host, and an IP target each return 404
• Bluesky and X avatar addresses return 200 through /_img/avatar. The trending page had no social rows in local data, so it was not checked in the browser
• Under wrangler dev, the second request for the same avatar returned CF-Cache-Status: HIT in 12 ms

SKILL.md badges	Home avatars

[harlan-github-agent]

🤖 MERGED

Harlan Agent Kit posted this automated review. It is not Harlan's personal review or approval. AI open source policy. Last updated: 2026-09-21 06:54 UTC.

GitHub merged this pull request.

No material findings were recorded.

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