AIC: Packages Need an Interface for Coding Agents

I develop several tightly related repositories at the same time. Some are reusable SDKs for declarative schemas, infrastructure, stateful workflows, and other domain abstractions. Others are applications that consume several of those SDKs together. The development loop constantly crosses package boundaries. SDK A ──────┐ │ SDK B ──────┼──▶ application │ │ SDK C ──────┘ │ ▲ │ └──── feedback ───┘ I've already written about why I don't think this requires a monorepo, and why I prefer the repository itself to carry the current source of truth: AI Agents Don't Need a Monorepo. They Need a Readable Codebase The Repo Is the Context: Why Agents Don't Need History I won't repeat those arguments here. This post starts one layer later. As these SDKs became more agent-aware, each package started needing to tell coding agents how it should be used. I was already using project-local surfaces such as .claude/ , .codex/ , AGENTS.md , and package-specific skills. They are useful. Explicit project-local context works. The maintenance was the awkward part. When an SDK changed, I would tell the agent to update the corresponding instructions, rules, or skills in the consuming repository. That worked too. But after doing it repeatedly across several packages and repositories, I noticed something: My repeated update instructions had quietly become an undocumented protocol. Which files should change? Which source is canonical? What should be copied? What should only be referenced? What belongs to the package, and what belongs to the consuming repository? How should different coding-agent harnesses receive the same package knowledge without creating independent copies? I initially thought I needed a better synchronizer. I now think the problem is one layer higher. Packages already have an interface for programs. They increasingly need an interface for coding agents. I've been calling the protocol I'm using for that interface AIC — Agent Index Convention . It is still a draft from my own dev