# AGENTS.md

Machine entry point for AI coding agents working in this repo. The authoritative
guidance for humans lives in [CONTRIBUTING.md](./CONTRIBUTING.md) and
[README.md](./README.md); this file only points at it and states the stable
first-action facts. Do not restate evolving prose here — it will drift.

## First action

- Project: F#-style pattern matching for TypeScript/ESM. Node `>=26` (pinned via `.node-version`), ESM-only (no CommonJS shim).
- **Mandatory while iterating:** `npm run test` (runs `check:tsc`, then the unit suite). This is the gate you are responsible for.
- **On commit:** write a good message (see [CONTRIBUTING.md § Commit messages](./CONTRIBUTING.md#commit-messages)). Lefthook's pre-commit hook already runs the fast, offline, staged-file checks (`tsc` + `oxlint` + `oxfmt` + `cspell`) — don't run them by hand. If the hook fails on style, `npm run fix`, restage, recommit.
- **`npm run check` is NOT part of the feature loop.** It adds `knip` (dead-code/deps) and `check:outdated` (registry) — repo-maintenance scans. Run it only on an explicit maintenance / update-deps branch; CI runs it on the PR regardless.

    ```sh
    npm run test   # the bot's definition of done; commit normally after
    ```

## Never do

Don't silence the type system to force a green run. As an agent these are forbidden:

- `// @ts-nocheck`, `// @ts-ignore`, `// @ts-expect-error`
- `// oxlint-disable` / `// oxlint-disable-next-line`
- `as` casts used to push an expression through (type-aware oxlint already flags unsafe assertions)

Fix the root cause with the type system instead — narrowing, generics, `satisfies`, conditional / mapped types, utility types (`NonNullable`, `Exclude`, …). TypeScript can express it; that's the intended tool. The `oxlint-disable`-location rule in [CONTRIBUTING.md § Rules the tools don't enforce](./CONTRIBUTING.md#rules-the-tools-dont-enforce) is a **human** last-resort convention (so a reviewer can spot a deliberate suppression) — it is not permission for you to add one. If the types genuinely cannot express something, stop and surface the conflict (commit message / MR) rather than suppress it.

The same applies to the checks themselves: **never `git commit --no-verify`** (or otherwise skip a pre-commit / pre-push hook). The checks are fast and offline, so a redundant run is fine — bypassing a hook to get green is the identical anti-pattern. If a commit already skipped a hook, redo it through one: `git reset --soft HEAD~1 && git commit -C <skipped-sha>`.

## Read these

- [CONTRIBUTING.md § Rules the tools don't enforce](./CONTRIBUTING.md#rules-the-tools-dont-enforce) — the constraints the linters don't catch; CI/review bounce these. **The most important section.**
- [CONTRIBUTING.md § Script prefix convention](./CONTRIBUTING.md#script-prefix-convention) — adding an `npm run` script? reuse an existing prefix or it doesn't belong.
- [CONTRIBUTING.md § Commit messages](./CONTRIBUTING.md#commit-messages) — gitmoji + imperative + 50/72.
- [CONTRIBUTING.md § Feedback tiers](./CONTRIBUTING.md#feedback-tiers) — what runs when (`watch` / pre-commit / pre-push / `check` / `fix` / CI).
- [README.md § Tooling decisions](./README.md#tooling-decisions) — the rationale behind each tool choice; read before changing tooling.
- [package.json `#scripts`](./package.json) — the source of truth for every command (the `LEFTHOOK_FILES` convention scopes them to staged files vs. the whole project).