Infer AuthUser / AuthSession from auth.ts: plugin and additionalFields columns are missing from c.get('user'), getUser() and requireAuth() #567

Description

AuthUser and AuthSession are always Better Auth's base shapes, whatever auth.ts configures. Fields added by plugins (role and banned from admin(), impersonatedBy on the session) or by user.additionalFields are present at runtime but missing from the types of c.get('user'), c.get('session'), getUser(), getSession() and requireAuth(c).

The app can't fix this itself:

• Redeclaring user on CloudContextVariables fails with TS2717, because the property already has a different type.
• AuthUser is a type alias, so it can't be augmented.

A cast at every read is the only option.

Void already has the information. defineAuth<T>(config: T): T keeps the config type, and .void/better-auth-schema.ts is generated with the plugin columns.

Steps to reproduce

1. Enable auth and add auth.ts with a plugin and a custom field:

   // auth.ts
   import { admin } from 'better-auth/plugins/admin';
   import { defineAuth } from 'void/auth';
   
   export default defineAuth(({ defaults }) => ({
     ...defaults,
     plugins: [admin()],
     user: { additionalFields: { plan: { type: 'string', required: false } } },
   }));

2. Read the fields on the server:

   import { defineHandler } from 'void';
   import { getUser } from 'void/auth';
   
   export const loader = defineHandler((c) => ({
     role: c.get('user')?.role,
     plan: getUser()?.plan,
   }));

3. Run tsc.

Actual behavior

error TS2339: Property 'role' does not exist on type '{ id: string; createdAt: Date; updatedAt: Date; email: string; emailVerified: boolean; name: string; image?: string | null | undefined; }'.
error TS2339: Property 'plan' does not exist on type '{ id: string; createdAt: Date; updatedAt: Date; email: string; emailVerified: boolean; name: string; image?: string | null | undefined; }'.

Trying to override the type:

declare module 'void' {
  interface CloudContextVariables {
    user: (AuthUser & { role: string | null }) | null;
  }
}

error TS2717: Subsequent property declarations must have the same type. Property 'user' must be of type '{ id: string; … } | null', but here has type '… | null'.

Expected behavior

c.get('user'), getUser() and requireAuth(c) include role, banned, banReason, banExpires and plan. c.get('session') and getSession() include impersonatedBy.

Cause

packages/void/src/runtime/auth.ts (main @ a6de7829bf, lines 6–7):

export type AuthUser = User;
export type AuthSession = Session;

User and Session come from better-auth without any options, so they're the base shapes. CloudContextVariables (runtime/handler.ts lines 29–31), AuthState, getUser, getSession and requireAuth are all typed from them.

Possible fix

Better Auth can already infer both types from the config type. This type-checks with the auth.ts above, and both role and plan are present:

import type { Auth } from 'better-auth';
import type config from './auth';

type Options = ReturnType<typeof config>;
type User = Auth<Options>['$Infer']['Session']['user']; // includes role, banned, plan
type Session = Auth<Options>['$Infer']['Session']['session']; // includes impersonatedBy

Void could generate this the way .void/env.d.ts augments ValidatedEnv and CloudBindings:

1. Make AuthUser and AuthSession interfaces: export interface AuthUser extends User {}.
2. Generate .void/auth.d.ts when auth.ts exists:

declare module 'void/auth' {
  interface AuthUser extends _InferredUser {}
  interface AuthSession extends _InferredSession {}
}

Everything typed from AuthUser, including CloudContextVariables, would then pick up the fields.

Workaround

Cast in one helper:

import { userTable } from '@auth-schema'; // .void/better-auth-schema.ts

type User = typeof userTable.$inferSelect;

export function getCurrentUser(c: CloudContext): User | null {
  return c.get('user') as User | null;
}

Environment

• void 1.2.1, better-auth 1.7.11
• TypeScript 7.0.2, vite-plus 1.3.0, Node 22.23.3, macOS 26.6