Ask HN: Anyone built a true omnichannel bot with shared session state?

Hi everyone. I am working for a client who wants to build a collection automation system using an omnichannel bot. The goal is to support email, SMS, voice or phone (VoIP or PSTN), and a chat widget on a website or app.

I have looked at tools like VAPI and similar vendors that offer voice, SMS and email, but I am not sure they qualify as true omnichannel solutions, especially when it comes to chat and keeping session context across different channels.

I would like to hear from anyone who has built or is currently building something like this.

What platforms or architectures are you using for omnichannel support bots across email, SMS, voice and chat?

How are you handling session state or context when users switch channels? For example, if someone starts on a chat widget, then replies over SMS or gets a follow up phone call, how do you keep everything tied together?

What have been the biggest technical challenges? Things like voice reliability, routing across channels, data sync issues, identifying the same user across different channels, or handing off to a human.

If you evaluated vendors that only supported two or three channels, like voice plus SMS plus email, did you run into limitations that forced you to build custom components?

Would appreciate any real world experiences or vendor recommendations. Thanks.