Subscription and checkout-session writes on the REST API and the MCP
subscription_create tool now refuse a product_type that starts with
platform- (422 reserved_product_type). That prefix belongs to LinkSell's
own plan billing. Caller metadata keeps your own keys, but keys that
start with x402_ and the platform-billing keys are stripped before the write,
and interval_count is capped at 365. Plan grants on LinkSell's side now come
only from a server-created purchase record, never from fields a caller can set.
This note records shipped behavior as of . Planned work remains on the public roadmap until release.