Third-party host page embedding the production widget pointed at the
paid-demo tenant — a writable mirror of Demo that is
exempt from demoReadonlyGuard. Origin
paid-demo-host.lanebooker.ca is in paid-demo's
allowed_origins so the HMAC handshake completes. This
page is the canonical surface for end-to-end booking tests that need
a real D1 INSERT (B5, B6, B10, B11) without touching real-client
data (the-alley-os, the-alley-hanover) or breaking Demo's read-only
showroom guarantee.