users.vitanova.network:456 flatly 403s the CORS preflight for
https://admin.gorbushka.market (no CORS headers at all) while
https://novo.market gets a full grant (204, explicit
Access-Control-Allow-Origin + wildcard Allow-Headers). This is a
server-side origin allowlist, not something the frontend can route
around - confirmed live via curl OPTIONS against both origins.
This makes item 1 (X-Marketplace-Domain CORS confirmation) load-bearing
for the gorbushka admin login fix in progress on the marketplaces repo:
the frontend fix is ready but cannot work until this origin is added.
