Styx wires seven coding agent CLIs into one app via four integration methods

The open-source Styx app runs seven coding agent command-line tools plus a plain shell on the same projects. Its developers found there is no single way to control an agent from another program, so they use four approaches: streaming JSON, a dedicated app server, the Agent Client Protocol, and an embedded terminal. Each method has trade-offs, such as whether mid-turn messages can be sent or whether approvals can be answered from outside the agent's own interface. A small router selects the right method per agent, so the rest of the app sees a uniform session type. The team also tests with fake CLI binaries to avoid contacting real providers or accounts.