The mobile app communicates with a dedicated server running on Raspberry Pi & Pisound via Bluetooth. It is called Pisound Control Server (pisound-ctl) and it allows listing all supported patches in a predefined location and to selectively launch the patches in the appropriate software, making headless browsing and switching between patches easy, as well as executing custom scripts.
The stdout and stderr outputs of the launched application are displayed in real time, informing the user on what is going on with the patch application.
The design is extensible - new scripts may be added to support launching patches on more audio applications, see the Customization section in the documentation linked below for more details.
More information is available at https://blokas.io/pisound/docs/pisound-app