`SessionManager` type not exported from public API, causing type inference issues

Description

When using useSession and wrapping it in a function (common pattern for creating a typed session helper), TypeScript cannot infer the return type without a reference to internal module paths.

Expected Behavior

The SessionManager type should be exported from @tanstack/react-start/server (and equivalent for solid/vue) so users can properly type their session helper functions.

Actual Behavior

Only SessionConfig is exported from the public API. SessionManager is defined in session.ts but not re-exported through index.ts.

This causes the following TypeScript error:

The inferred type of 'getAppSession' cannot be named without a reference to 
'../../../../../../node_modules/.pnpm/@tanstack+start-server-core@1.150.0/node_modules/@tanstack/start-server-core/dist/esm/session'. 
This is likely not portable. A type annotation is necessary.

Reproduction

// utils/session.ts
import { useSession } from '@tanstack/react-start/server'

type SessionData = {
  userId?: string
}

// ❌ This causes type error - cannot infer return type
export function useAppSession() {
  return useSession<SessionData>({
    password: process.env.SESSION_SECRET!,
  })
}

Workaround

Currently users must derive the type manually:

import { useSession } from '@tanstack/react-start/server'

type SessionData = { userId?: string }

// Derive SessionManager type since it's not exported
type AppSessionManager = Awaited<ReturnType<typeof useSession<SessionData>>>

export function useAppSession(): Promise<AppSessionManager> {
  return useSession<SessionData>({
    password: process.env.SESSION_SECRET!,
  })
}

Suggested Fix

Export SessionManager, Session, SessionData, and SessionUpdate types from @tanstack/start-server-core/src/index.tsx:

// packages/start-server-core/src/index.tsx

- export type { SessionConfig } from './session'
+ export type { SessionConfig, SessionManager, Session, SessionData, SessionUpdate } from './session'

These types are already defined and used internally in request-response.ts, they just need to be re-exported publicly.

Environment

• @tanstack/react-start: 1.149.4 / 1.150.0
• @tanstack/start-server-core: 1.150.0
• TypeScript: 5.x
• Node: 22.x

Additional Context

The official documentation shows the useAppSession() pattern but doesn't mention this typing issue:

• https://tanstack.com/start/latest/docs/framework/react/guide/authentication

The types exist in packages/start-server-core/src/session.ts:

• SessionManager<T> (lines 42-47)
• Session<T> (lines 33-37)
• SessionData<T> (line 32)
• SessionUpdate<T> (lines 39-40)

Start with packages/start-server-core/src/session.ts to review the existing SessionManager, Session, SessionData, and SessionUpdate types, then inspect their exports in packages/start-server-core/src/index.tsx. Verify the public @tanstack/start-server-core exports and confirm the useAppSession reproduction no longer requires an internal module path or manual derived annotation.