How to create 3p apps in Zendesk marketplace that can handle conversations starting from zendesk web and handoff to zendesk /human agent ?

Hello

I want to build an app that can sit in front of human agents over zendesk web chat. I see there are a few of these apps here https://www.zendesk.com/marketplace/apps/?utm_medium=zendesk_support&utm_source=marketplace_directory_my_apps_link&class.name=AI+and+Bots. Can you help me on how i can build such an app ? This is not for any specific business but want to ultimately make it available as an installable app. Thanks