//! The agent layer, which drives one `pi` subprocess over its JSONL protocol.
/// Drives one agent process and reports what it says.
/// A turn's delegated questions, and what they cost it.
/// Reads a delegation request out of what the agent asked for.
/// Splits the agent stream into whole JSONL records.
/// The shapes the agent speaks in, and the readers for them.
/// The arguments a launcher is given for one session.