app-server: allow dynamicTools to be updated after thread/start

What variant of Codex are you using?

App Server

What feature would you like to see?

Codex app-server currently accepts dynamicTools only on thread/start.

Please add an app-server API to update the dynamic tool registry after thread creation, and ideally make newly-added tools available at the next model continuation boundary within the active turn.

My use case for this is sometimes I start a large conversation/feature and then half way through think, wow now I want to use this tool, but with the current app-server endpoints I am unable to do this.

Also sometimes I don't want a tool available to a model for every single turn for security reasons etc.

Additional information

_No response_