verify authorization before operations

Always verify that users have proper authorization to access and modify resources before performing any data operations. This prevents privilege escalation attacks and unauthorized data access.

Key principles:

1. Check visibility first: Ensure users can see/access the resource before allowing any operations on it
2. Validate operation permissions: Verify the user has specific permissions for the intended operation (read, write, delete)
3. Prevent impersonation: Never allow users to change ownership or creator fields to other users, as this constitutes impersonation

Example implementation:

async update(tx, change: UpdateValue<typeof schema.tables.issue>) {
  // First verify user can access the resource
  await assertIsAdminOrCreator(tx, tx.query.issue, change.id);
  
  // Then perform the operation
  await tx.mutate.issue.update(change);
}

// In permissions schema
select: [
  (authData, {exists}) =>
    exists('issue', q => q.where(eb => canSeeIssue(authData, eb))),
]

This pattern prevents scenarios where users could perform operations on resources they cannot see due to permission changes, and ensures consistent security enforcement across all data access patterns.