Treat pi as a black box first: 4 run modes, session tree persistence, mid-conversation model switching, Enter vs Alt+Enter message interjection, /tree branch navigation. Builds intuition for the architecture parts that follow.
This 17-part series takes you from CLI user perspective through pi-mono's Agent Loop, Session Tree, Tool System, Extension System, TUI Architecture, Remote Session, Telemetry, Compaction, and Release process. Ideal for developers wanting to self-host agents, research agent architecture, or contribute to pi.
SessionManager core: JSONL append-only storage, id/parentId tree formation, branch() moves leaf pointer without mutating history, buildSessionContext() handles compaction entries, createBranchedSession() forks to new file. Complete Entry types: message, thinking_level_change, model_change, compaction, branch_summary, custom, custom_message, label, session_info. Migration v1→v2→v3 details.