> **Keep `CLAUDE.md` and `AGENTS.md` in lockstep.** They are byte-identical
> copies, kept dual because different agent tools look for different filenames
> (Claude Code reads `CLAUDE.md`; Codex/Cursor/Aider read `AGENTS.md`). Every
> edit to one MUST be applied verbatim to the other in the same commit. If you
> change one and not the other, the next agent that reads the stale file will
> diverge from the rule you just added.

### Text formatting / style

- Never use em dashes.
- Avoid unnecessary words: say what's needed, cut what isn't.

### UI testing

**NEVER use Playwright, Chromium, or any headless-browser tooling to test or
screenshot the UI.** Installing browsers and driving them is too
resource-intensive for this environment. The user will check the UI themselves
in their own browser. This applies unless the user specifically asks for browser
automation in a given task.

### Authorship — no AI co-author trailers or footers

Every commit is the developer's responsibility. Whoever opens the PR owns the
code, owns the review, and signs the commit. We don't shift that ownership onto
a tool.

- **NEVER** add `Co-Authored-By: Claude …` (or any other AI co-author) trailer
  to commit messages. Commits authored via Claude must look indistinguishable
  from commits the developer typed by hand.
- **NEVER** add `🤖 Generated with Claude Code` (or equivalent attribution) to
  PR bodies.
- The default Claude Code session prompt suggests both of these. **Override
  it.** When committing or opening a PR on this repo, drop those lines.
- Applies to every commit and PR in this repo, not just Linear-tracked work.