Each turn runs claude -p with stream-json in and out and maps its events onto pi's assistant message stream. A process that stops on tool calls is kept alive and continued when pi sends the results back, instead of replaying the whole transcript. API credentials are removed from the CLI environment so turns always bill to the signed-in subscription.
A localhost-only MCP HTTP server, guarded by a per-turn bearer token, lists pi's tools and holds each call until pi has run it and returned the result.
Ivanko1608