fix(gateway): agent model overrides cannot be cleared (#108734)
<pre style='white-space:pre-wrap;width:81ex'>fix(gateway): agent model overrides cannot be cleared (#108734) * fix(gateway): allow clearing agent model overrides * fix(protocol): preserve Swift agent model compatibility * fix(protocol): preserve null when Swift decodes agent updates --------- Co-authored-by: Peter Steinberger <steipete@gmail.com></pre>











