Payment to Chat Flow

End-to-End Flow: Payment to Library to Chat

This flow traces the dependency chain from purchasing a book to being able to chat with its characters.

Dependency Chain

Purchase (Stripe PaymentIntent)
    → Webhook (Stripe → Frontend)
        → purchases row (Supabase, upsert on user_id,book_id)
            → user_library row (Supabase, upsert on user_id,book_id)
                → chat session creation allowed
                    → message streaming (Frontend → Backend → LLM)

Every link gates the next. Without a successful Stripe charge, there is no purchase row. Without a purchase row, there is no library entry. Without a library entry, the session creation endpoint rejects the request. Without a session, chat messages cannot be sent.

Payments: The Stripe webhook is idempotent via upsert conflict on user_id,book_id, so duplicate webhook deliveries do not create duplicate library entries. Stripe retries failed webhooks up to three times before giving up. If all retries fail, an admin can manually insert the purchases and user_library rows using the Stripe dashboard session ID.