Add Pi as a supported host

Traceability

• Spec ID: pi-host-support
• Status: Implemented
• Contribution workflow: Contributing a New Coding Agent Host

Intent

Make Pi (pi.dev, @earendil-works/pi-coding-agent) a first-class, evidence-safe Better Harness host alongside Qoder, Codex, Claude Code, Cursor, Qwen Code, and GitHub Copilot.

This contribution reaches the Verified install/discovery capability level: native discovery, configured assets, session evidence, evidence-bundle routing, and portable report routing are verified. Pi remains outside the public Quickstart set until a full report render is validated end to end in Pi, as required by the repository's host contribution contract.

Pi is a minimal terminal coding harness extended through TypeScript extensions, skills, prompt templates, themes, and pi packages. It already implements the Agent Skills standard and auto-discovers a package's skills/ directory, so pi install <repo> can load the canonical better-harness Skill today. The gaps this spec closes are the missing native slash-command entry point and, more importantly, the missing evidence: every provider enum rejected pi, so the workflow could neither inventory Pi's configured assets nor read Pi session transcripts, leaving a Pi user unable to get a Pi-scoped Harness report.

Pi's native contracts were verified against @earendil-works/pi-coding-agent: the agent dir resolves from PI_CODING_AGENT_DIR (default ~/.pi/agent); sessions are JSONL trees whose default location is