The tanstack-db-web-starter template fails to run due to a better-auth compatibility issue with TanStack Start.

The error

TypeError: Cannot read properties of undefined (reading 'body')
      at get body [as body] (node:internal/deps/undici/undici:9946:29)
      at getBody ([email protected]/src/utils.ts:7:15)
      at processRequest ([email protected]/src/router.ts:191:14)

Steps to reproduce

npx gitpick electric-sql/electric/tree/main/examples/tanstack-db-web-starter my-tanstack-db-project
cd my-tanstack-db-project
pnpm install
pnpm dev

Try and login. Auth fails with the above error.

Environment

• Node.js: 20.19.0 (also fails on 22.12.0)
• better-auth: 1.4.2
• better-call: 1.1.0
• TanStack Start: 1.139.6
• Vite: 7.2.4

Attempted fix

Adding the tanstackStartCookies() plugin to src/lib/auth.ts (as recommended in better-auth docs) does not resolve the issue.

Impact

This blocks the @electric-sql/start quickstart package from being deployed, as generated apps fail immediately on startup.