Canvas's browser-side code (auth.ts, api.ts, billing.ts) all call
fetch(PLATFORM_URL + /cp/*). PLATFORM_URL comes from
NEXT_PUBLIC_PLATFORM_URL at build time; with the build arg unset,
it falls back to http://localhost:8080 in the compiled bundle.
That means on a tenant like hongmingwang.moleculesai.app, the
user's browser actually tried to fetch http://localhost:8080/cp/
auth/me — which resolves to the USER'S OWN machine, not the tenant.
Login redirect loops 404. Every tenant canvas has been unable to
complete a fresh login on this path; existing sessions only worked
because the cookie was already set domain-wide.
Fix: pass NEXT_PUBLIC_PLATFORM_URL=https://api.moleculesai.app
as a build arg in the tenant-image workflow. CP already allows
CORS from *.moleculesai.app + credentials, and the session cookie
is scoped to .moleculesai.app so tenant subdomains inherit it.
Verified in prod by rebuilding canvas locally with the flag and
hot-patching the hongmingwang instance via SSM. Baked chunks now
contain api.moleculesai.app; browser auth redirects resolve
cleanly to the CP.
Self-hosted users override by rebuilding with their own URL —
same pattern molecule-app uses with NEXT_PUBLIC_CP_ORIGIN.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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