fix(api): advertise the API catalog relation

[nibzard]

What changed

• advertise /.well-known/api-catalog through the global HTTP Link header with rel="api-catalog"
• preserve the existing llms.txt and llms-full.txt alternate relations
• change the catalog service-description hint from application/openapi+json to the media type the canonical API endpoint actually serves: application/json
• add runtime regressions for RFC 9727 HEAD discovery and normal-page advertisement

Why

The JSON Linkset existed and had the correct response content type, but its HTTP discovery contract was incomplete. A HEAD request did not advertise the required api-catalog relation, and the catalog described a different OpenAPI media type than the canonical API endpoint returns.

Live verification on 2026-07-30 confirmed https://api.steel.dev/sdk-openapi.json returns HTTP 200 with Content-Type: application/json; charset=utf-8.

Impact

Agents and API tooling can discover the catalog from both the well-known endpoint and regular docs responses without losing the existing Markdown alternates.

Validation

• bun test — 297 passed
• bun run typecheck
• bun run check --error-on-warnings
• bun run validate-links
• bun run build
• git diff --check

[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Actions	Updated (UTC)
docs	Ready	Preview	Jul 30, 2026 6:48pm