TanStack Start billing and setup updates

The experimental TanStack Start template source now includes Stripe and Polar billing paths, purchase confirmation email, and updated local setup guidance. The selected provider handles new checkout while existing billing remains with its original provider.

The sign-in, sign-up and password setup forms now specify POST for native submission. Sign-in and sign-up keep their disabled fields until the native handlers hydrate. On both pricing pages, Test payment details opens the provider selector and test card instructions when the test-only demo is enabled. The included /docs/features/test-billing-demo guide covers local setup and the guest and subscription paths.

For an existing Start project, apply the two forward Polar migrations using the retained-database upgrade guide without resetting retained data. Configure Stripe Price IDs or Polar Product IDs for the offers you sell, and rebuild after changing public settings. Unmapped offers remain unavailable in both test and live modes. Follow the matching billing guide and configure the provider and email mode for your environment before testing. These source changes do not update a hosted deployment. See the Start hosted deployment status.

The Docs now start with a shared Quickstart and Application Architecture. Shared guides bring framework-specific examples together and remember your selected example across pages; native setup and deployment guidance remains explicit.