project-behavior

Bootstrap or extend a project's AGENTS.md with one or more behavior packs — short, opinionated preambles that set the rules agents must follow when working in the project. Karpathy's four-section preamble is included as the default pack; additional packs can be added by dropping more files into references/.

When to invoke

Brand-new project that needs an AGENTS.md from scratch.
Existing AGENTS.md that lacks a behavioral preamble.
Switching or stacking behavior packs (e.g. add a security-focused pack on top of Karpathy).
Pairing with canonical-project-skills-layout: that skill enforces the file layout (where AGENTS.md lives, that CLAUDE.md is @AGENTS.md); this skill controls the content of AGENTS.md.

Workflow

Locate the guide. Look for <project>/AGENTS.md. If it doesn't exist but <project>/CLAUDE.md does, ask whether to (a) rename/promote CLAUDE.md to AGENTS.md and replace CLAUDE.md with @AGENTS.md, or (b) write directly into CLAUDE.md. The canonical answer is (a); recommend it unless the user is on a Claude-only project.
Detect existing preamble. Read the first ~30 lines of AGENTS.md. If the H1 is # Agent behavioral guidelines or any pack's first line is already present verbatim, the preamble is installed — skip ahead and ask whether to add another pack on top, swap it, or exit.
Pick pack(s). List the files under references/ to the user with a one-line summary of each. Default: karpathy.md. Allow multi-select for stacking.