Maintain reusable project knowledge with Project Cairn

Use Project Cairn when an operator wants an agent to run project-knowledge maintenance during day-to-day work instead of relying on chat history or informal notes. The agent can manage initialization or retrofit work for AGENTS.md, .cairn/config.yaml, and cairn/ notes; record meaningful progress in LOG.md and ROADMAP.md; review topic notes for current conclusions; audit stale or missing records; search and cite external knowledge only when it shapes the work; extract reusable lessons; and generate human-approved graduation candidates for Obsidian, Notion, or Lark / Feishu knowledge bases. Invoke this during agent-assisted project setup, after meaningful implementation or research turns, before closing exploration branches, or when a verified lesson should become reusable outside the current repository. The boundary is explicit: this is not a background memory product, generic note-taking app, CLI listing, or normal documentation framework. It is a skill-loaded operator workflow with documented triggers, templates, references, provider adapters, reviewable outputs, and human confirmation before long-term knowledge-base writes.