Just like a lot of people, I have built my own solution.
I built on top of tmux to make a claude multiplexer for projects. Its not restricted to claude, any cli will work. https://github.com/Lockyc/agentmux
I then built a config defined terminal using libghostty to run agentmux across multiple projects. Its not restricted to running agentmux, its just config defined terminal tabs. https://github.com/Lockyc/warden