Native chat for third-party agents: pi (pi-coding-agent) adapter / public session-host contract #21558

What

Request native chat (structured session) support for third-party coding agents — concretely pi — or, more generally, a documented adapter contract for the session host that native chat already uses for Claude and Codex.

Why

• Native chat has become the best surface in Orca for agent work: structured turns, tool rows, diff cards, session history, rewind, slash commands, mobile. Today it is closed to two first-party agent kinds (Claude via the Claude Agent SDK, Codex).
• The session-host abstraction is already agent-agnostic in shape — Claude and Codex render through the same UI, there is one / picker for every agent, and orchestration can drive "native-born structured chat sessions". A documented adapter contract would let the ecosystem plug agents in instead of forking the TUI path.
• pi is a strong first candidate because it ships an embedding SDK built for exactly this:
  • @earendil-works/pi-coding-agent → createAgentSession() with subscribable event streams (message_update / assistantMessageEvent.type: "text_delta"), programmatic session.prompt(), file-backed or in-memory session managers.
  • First-class resources: extensions, skills, prompt templates, themes, context files; multi-provider model registry via ModelRuntime.create().
  • Durable JSONL session transcripts that map naturally onto Agent Session History / resume.
  • Fully headless when driven via the SDK — no PTY/TUI required, matching the structured-session delivery path Orca already implements for Claude/Codex.

Ask

1. Document the session-host / structured-agent contract (launcher, turn events, tool progress, question/ask flow, session persistence) so third-party agents can target it.
2. Ideally, ship a pi adapter natively. Happy to help test on headless Linux (server runtime) plus Windows and macOS clients.

Environment

• Orca server: headless Linux, v1.4.203
• Desktop clients: v1.4.205 (macOS, Windows)