GET /catalog walks agents through progressive disclosure: available
APIs with descriptions, then one API's tags, then a tag's endpoints,
then full detail for a single operation with $refs resolved inline.
Oversized tags (tag-poor upstreams) fall back to path-prefix groups,
drillable with ?prefix= and compressed through single-child chains.
Responses are filtered to the key's grants, carry ETags for cheap
revalidation, and reuse the discovery spec cache. Key auth is shared
with the docs portal via portal.resolve_api_key; 'catalog' and 'mcp'
are now reserved slugs.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
