chore: add AGENTS.md with repo context for agents

[MattPereira]

Summary

• Adds AGENTS.md at the repo root covering commands, the Anvil-fork testing model, the protocolVersion (V1 CowAmm / V2 / V3) dispatch pattern, data providers, ABI/address-map locations, and conventions (Biome, dpdm, typed error factories, changesets).
• Adds .agents/skills/changeset/SKILL.md — a tool-agnostic skill that tells agents to write .changeset/<slug>.md directly (since pnpm changeset is interactive and can't be driven from an agent), with bump-selection rules and a "when to skip" guard so PRs touching src/** don't ship without release notes.
• Follows the emerging cross-agent convention so Claude Code, Cursor, Codex CLI, and similar tools can all load a single context file instead of per-tool files.

Why this helps agent work on this repo

• Saves tokens. Without it, a cold agent spends thousands of tokens re-exploring src/, test/, package.json, vitest.config.mts, biome.json, and the deployment maps every session just to rediscover that V2/V3/CowAmm are dispatched off protocolVersion, that each test spins up its own Anvil fork at a pinned forkBlockNumber, that @/* maps to src/*, and where contract addresses live. That context is now one read away.
• Raises answer quality. The file documents non-obvious invariants — the query / buildCall / buildCallWithPermit2 entity contract, maxForks: 3 cap, per-pool-type input validators, pnpm update:deployments instead of hand-editing address maps, changeset-gated releases — so agents extend existing patterns rather than inventing new ones or producing plausible-but-wrong suggestions.

Test plan

• Skim rendered AGENTS.md on GitHub for accuracy
• Confirm documentation-only — no source or CI changes

🤖 Generated with Claude Code

[MattPereira]

checkout docs for the emerging standards if interested to learn more:

• https://agents.md/
• https://agentskills.io/home

scaffold ETH has pretty good example of finely tuned AGENTS.md:

• https://github.com/scaffold-eth/scaffold-eth-2/blob/main/AGENTS.md

[brunoguerios]

That's a great addition 👏
I've been navigating SDKs from other organizations and these files help a lot.
Thanks for the initiative 🙏

[johngrantuk]

Nice, thanks Matt.