Pi Agent Integration: Message Parsing, Retry, and Cancellation
When integrating a CLI-based AI agent, you can't avoid three things: how to translate its private event stream into stable messages, who's responsible for retry after failures, and how to cleanly stop the process when users click cancel. These three things essentially boil down to "clarifying responsibilities"—it's simple in theory, but you only realize how deep the water is when you actually do it.
Background
Recently, I've been working on an AI coding assistant project, and one of the agents to integrate is pi. It's a TUI/CLI coding agent that outputs JSON events line by line to stdout when running. Sounds simple—spawn the process, read output, parse it—but when you actually start, you realize "integrating an agent CLI" is completely different from "integrating a regular CLI."
With a regular CLI, you read stdout, get an exit code, and that's it. But agent CLIs have three particularly headache-inducing characteristics:
