pi-cordis: Integrating the Pi Coding Agent into the Cordis Runtime

`pi-cordis` is a tool for integrating the Pi coding agent as a Cordis runtime plugin. It provides Pi SDK sessions through the host’s Cordis tree, decoupling Pi from the host application’s lifecycle. Developers can flexibly mount, remove, or replace Pi without requiring Pi to take over full management. The plugin provides capabilities such as `engine:pi` and supports either in-memory or persistent sessions, making it well suited for scenarios in the DSH ecosystem that emphasize architectural decoupling and flexible invocation.