Can't grant Permission.read() for another user - what's the solution?

I'm building a therapist-client app. When a client creates a document, how do I give their therapist read access?

The Problem

// Client creates a document
databases.createDocument(
  permissions: [
    Permission.read(Role.user(clientId)),        // ✅ Works
    Permission.read(Role.user(therapistId)),     // ❌ Error: Can't grant permission for another user
  ]
)

I can only grant permissions I already have. The client can't grant permissions on behalf of the therapist.

My Situation

• 1000 clients
• Each client has 1 assigned therapist
• Clients create ~10 documents per day
• Therapists should ONLY see their assigned clients (not other therapists' clients)

What Should I Use?

Option 1: Cloud Function

• Run a function every time a client creates a document
• Function adds therapist permission using Server SDK
• Problem: 10,000 function calls per day = expensive

Option 2: Teams

• Create a team for each client-therapist pair
• Use Role.team(teamId) for permissions
• Problem: Is 1000 teams too many? Will it be slow?

Option 3: Server Function for Reads

• Clients create docs with only their own permissions
• Therapists call a function to fetch data
• Function validates and returns data using Server SDK
• Problem: Adds latency when therapist views data

Option 4: Anything else?

My Question

Which approach is best? Are 1000 teams okay, or should I use functions?