W003: Update user

Updates the authenticated user's own profile record (currently displayName).

Steps

1. Verify the Firebase token. Resolve firebaseUid and the platform user row.
2. Apply the patch. Call Platform.updateUser(userId, { displayName }) with only the supplied fields.

Returns

{ user: { id, firebaseUid, email, displayName } }.

Business rules

• Self only. A user can update only their own record; there is no admin path to edit another user's profile here.
• Identity is Firebase-owned. Email and Firebase UID are not editable through this workflow.

Errors

• NotFoundError. No users row for the verified identity.
• ValidationError. displayName out of range.