[vue-db] useLiveQuery returns array type for data even when using findOne()

[sergeyd108]

• I've validated the bug against the latest version of DB packages

Describe the bug

When using useLiveQuery from @tanstack/vue-db with .findOne(), the data property always returns an array (T[]) instead of a single object (T | undefined). This behavior differs from @tanstack/react-db, where findOne() correctly returns a single object.

The UseLiveQueryReturn interface in Vue adapter has data hardcoded as ComputedRef<T[]>, which ignores the .findOne() modifier.

To Reproduce

1. Create a Vue component using @tanstack/vue-db
2. Use useLiveQuery with .findOne() to fetch a single record:

import { useLiveQuery } from '@tanstack/vue-db'
import { eq } from '@tanstack/db'

const { data } = useLiveQuery((q) =>
  q.from({ users: usersCollection })
   .where(({ users }) => eq(users.id, 'some-id'))
   .findOne()
)

3. Log or inspect data.value
4. See that it returns an array [{ id: '...', ... }] instead of a single object { id: '...', ... }

Expected behavior

When using .findOne(), the data property should return T | undefined (a single object or undefined), not T[] (an array). This is how it works in @tanstack/react-db:

// React - works correctly
const { data } = useLiveQuery((q) =>
  q.from({ users: usersCollection })
   .where(({ users }) => eq(users.id, userId))
   .findOne()
)
// data type: User | undefined ✓

Screenshots

N/A

Desktop (please complete the following information):

• OS: Windows 11
• Browser: Chrome
• Version: latest

Smartphone (please complete the following information):

N/A (not mobile-specific)

Additional context

Package versions:

• @tanstack/db: 0.5.16
• @tanstack/vue-db: 0.0.92
• vue: 3.5.26

Current workaround:

const query = useLiveQuery((q) =>
  q.from({ users: usersCollection })
   .where(({ users }) => eq(users.id, userId))
   .findOne()
)

// Manually extract first element
const user = computed(() => query.data.value?.[0])

The issue appears to be in the UseLiveQueryReturn interface definition which doesn't account for the findOne() query modifier:

interface UseLiveQueryReturn<T extends object> {
  data: ComputedRef<T[]>;  // Always array, should be conditional based on findOne()
  // ...
}