Replace Prettier and ESLint with Biome as formatter and linter

.github/workflows/continuous-integration.yml

@@ -12,20 +12,6 @@ concurrency:
 permissions: {}
 
 jobs:
-  format:
-    runs-on: ubuntu-latest
-    permissions:
-      contents: read
-    steps:
-      - name: Checkout repository
-        uses: actions/checkout@v6
-
-      - name: Setup environment
-        uses: ./.github/actions/setup
-
-      - name: Check formatting
-        run: pnpm format:check
-
   lint:
     runs-on: ubuntu-latest
     permissions:

AGENTS.md

@@ -4,9 +4,9 @@
 
 1. **Plan first:** Create a detailed plan and get explicit user approval before
    making changes.
-2. **Quality gates:** Every change must pass `pnpm format:check`, `pnpm lint`,
-   `pnpm test`, and `pnpm build` (or `pnpm integrate` for the full pipeline)
-   before being considered complete.
+2. **Quality gates:** Every change must pass `pnpm lint`, `pnpm test`, and
+   `pnpm build` (or `pnpm integrate` for the full pipeline) before being
+   considered complete.
 3. **Documentation:** Update `README.md`, `AGENTS.md`, configuration files, and
    any other documentation affected by your changes. Clean as you go — take
    ownership of every file you touch.
@@ -53,7 +53,7 @@ not `behavior`, `licence` not `license`, `centre` not `center`).
 
 ### Package Management
 
-- **Package manager:** pnpm (`pnpm@12.3.4` via the `packageManager` field —
+- **Package manager:** pnpm (`pnpm@12.16.1` via the `packageManager` field —
   Corepack manages the exact version, never install pnpm globally)
 - **Node.js engine:** `>=24.20.0` (declared in `package.json` `engines`)
 - **Lock file:** `pnpm-lock.yaml` is committed. NEVER delete or regenerate it
@@ -66,35 +66,35 @@ not `behavior`, `licence` not `license`, `centre` not `center`).
 - **Babel plugin override:** `pnpm-workspace.yaml` redirects
   `@babel/plugin-proposal-private-methods` (deprecated upstream) to
   `npm:@babel/plugin-transform-private-methods@^7.29.7`. The 7.x line is the
-  correct target while `eslint-plugin-react-compiler@19.1.0-rc.2` resolves
-  `@babel/core` 7.29.x — the v8 plugin requires `@babel/core ^8.0.0` and fails
-  the strict peer gate. Revisit when the react-compiler plugin migrates to Babel
-  8
-- **p5 dev resolution pinned:** the devDependency `p5` is pinned to exactly
-  `2.3.2` because upstream `2.3.3` was published without its `types/` files
-  (despite the manifest declaring them), breaking type checking. The
-  `p5 >= 2.0.0` peer dependency contract is unchanged. Revisit when p5.js
-  republishes a complete 2.3.3+
+  correct target while `babel-plugin-react-compiler` resolves `@babel/core`
+  7.29.x — the v8 plugin requires `@babel/core ^8.0.0` and fails the strict peer
+  gate. Revisit when the react-compiler plugin migrates to Babel 8
+- **p5 dev resolution:** the devDependency `p5` tracks the latest complete 2.x
+  release (currently pinned to exactly `2.3.4` because upstream `2.3.3` was
+  published without its `types/` files despite the manifest declaring them,
+  breaking type checking — `2.3.4` republished them). The `p5 >= 2.0.0` peer
+  dependency contract is unchanged. Revisit the exact pin if a later 2.x release
+  ships incomplete types again
 - **Peer dependencies are a contract:** `p5`, `react`, and `react-dom` are peer
   dependencies. The library code must never import anything beyond these at
   runtime — `@p5-wrapper/common` and `react-error-boundary` are the only runtime
   dependencies
 
 ### Formatting and Linting
 
-- **Prettier** is the formatter (this project does not use Biome — do not
-  introduce it). Config lives at `config/prettier/prettier.json`, key rules:
-  `printWidth: 80`, `arrowParens: "avoid"`, `trailingComma: "none"`,
-  `proseWrap: "always"` (all Markdown prose is hard-wrapped at 80 columns),
-  imports sorted by `@trivago/prettier-plugin-sort-imports`
-- **ESLint** is the linter. Config lives at `config/eslint/eslint.config.ts` and
-  extends `eslint` recommended, `typescript-eslint` strict and stylistic, and
-  `eslint-plugin-react-compiler` recommended with project-aware TypeScript
-  parsing. Type-aware linting runs via `jiti` — keep the config a `.ts` file
-- **React Compiler:** The React Compiler ESLint rules are enabled. Components
-  must follow the Rules of React strictly — no manual memoisation where the
-  compiler can handle it, no mutating props or render-time side effects. Do not
-  disable these rules
+- **Biome** is the formatter and linter. Config lives at the repository-root
+  `biome.json`, key rules: 2-space indentation, double quotes, semicolons
+  always, `proseWrap: "always"` (all Markdown prose is hard-wrapped at 80
+  columns), imports organised by Biome's `assist` `organizeImports` action,
+  linter `recommended` preset plus `useBlockStatements: "error"`. The `$schema`
+  key points at `./node_modules/@biomejs/biome/configuration_schema.json` so it
+  always tracks the installed Biome version. `pnpm format` runs
+  `biome check --write .`; `pnpm lint` runs `biome check .` (formatting check
+  plus lint)
+- **React Compiler:** The React Compiler Babel plugin
+  (`babel-plugin-react-compiler`) is active in the build. Components must follow
+  the Rules of React strictly — no manual memoisation where the compiler can
+  handle it, no mutating props or render-time side effects
 - **No comments:** Do not add comments to source files. The code should be
   self-documenting. The only permitted exceptions are `@ts-expect-error` /
   `@ts-ignore` suppressions with a `@see` reference (see
@@ -112,34 +112,28 @@ not `behavior`, `licence` not `license`, `centre` not `center`).
   `paths` and `config/vite/common.ts` — and MUST be kept in sync when changed
 - **Import style:** Use `import { type Foo }` inline type imports, matching the
   existing code. Imports of contracts across the alias boundaries follow the
-  sorted import order enforced by Prettier
+  organised import order enforced by Biome
 - **Type assertions:** Avoid `as` casts in library code. No `@ts-expect-error`
   or `@ts-ignore` suppressions currently exist; if one is ever needed, it must
   carry a `@see` reference and be verified against upstream issue or PR links
-- **Version pinned to 6.0.3:** `typescript` is an exact pin
-  (`"typescript": "6.0.3"`, no caret), deliberately held back from v7.
-  typescript-eslint does not currently support TypeScript 7 — its
-  [supported range](https://typescript-eslint.io/packages/parser) is
-  `>=4.8.4 <6.1.0`, and the Go-based TypeScript 7 is not yet feature compatible
-  with the JavaScript-based v6 API that typescript-eslint builds on. Upstream
-  support is tracked in
-  [typescript-eslint#10940](https://github.com/typescript-eslint/typescript-eslint/issues/10940)
-  and cannot land before TypeScript 7.1.x at the earliest. Do not bump past
-  `6.0.x` or widen the pin without confirming upstream support. Do NOT run
+- **Version pinned to the latest 6.x.x:** `typescript` is an exact pin (no
+  caret), deliberately held back from v7. TypeScript 7 is Go-based and not yet
+  feature compatible with the JavaScript-based v6 API that the build toolchain
+  (`vite`, `vite-plugin-dts`, `@microsoft/api-extractor`) builds on. Do not bump
+  past `6.0.x` or widen the pin without confirming toolchain support. Do NOT run
   TypeScript 7 side by side with v6 as an interim measure — we wait for full
   feature parity before migrating, no half measures
 
 ### Quality Gates
 
 Every change must pass before being considered complete:
 
-- `pnpm format:check` — formatting
-- `pnpm lint` — linting
+- `pnpm lint` — formatting check + linting (Biome)
 - `pnpm test` — testing
 - `pnpm build` — type checking (`tsc`) plus component and demo builds
 
-`pnpm integrate` runs format check → lint → test → build in one command and is
-the closest local mirror of CI.
+`pnpm integrate` runs lint → test → build in one command and is the closest
+local mirror of CI.
 
 ### Git Safety
 
@@ -264,7 +258,8 @@ legally certify a contribution — the human submitter reviews the AI-generated
 code, takes full responsibility for it, and adds any certification trailers
 themselves. Following the rules the Linux kernel team enforce for AI coding
 assistants, an agent's role in a commit ends at the message body — no
-`Signed-off-by`, no `Co-authored-by`, no other trailers or sign-offs. See [AI
+`Signed-off-by`, no `Co-authored-by`, no other trailers or sign-offs. See
+[AI
 Coding Assistants — The Linux Kernel documentation]
 (https://docs.kernel.org/process/coding-assistants.html), integrated into this
 ruleset on 2026-09-03.
@@ -369,9 +364,8 @@ Everything exported from `src/main.tsx` is public API and semver-protected:
 ├── tests/                     # Vitest tests for component behaviour
 │   ├── components/
 │   └── setup.ts               # Test bootstrap (canvas mock, cleanup)
+├── biome.json                 # Biome formatter + linter config (repo root)
 ├── config/
-│   ├── eslint/eslint.config.ts
-│   ├── prettier/prettier.json
 │   └── vite/
 │       ├── vite.config.ts     # Mode switch: lib (test + library) vs demo
 │       ├── common.ts          # Shared path aliases
@@ -412,24 +406,22 @@ Everything exported from `src/main.tsx` is public API and semver-protected:
 | :--------------------- | :--------------------------------------------------------- |
 | `pnpm install`         | Install dependencies (updates lockfile — commit the diff). |
 | `pnpm dev`             | Run the Vite dev server with the demo app.                 |
-| `pnpm format`          | Format all files with Prettier.                            |
-| `pnpm format:check`    | Check formatting without writing.                          |
-| `pnpm lint`            | Run ESLint (type-aware).                                   |
-| `pnpm lint:fix`        | Run ESLint with autofix.                                   |
+| `pnpm format`          | Format and lint-fix all files with Biome.                  |
+| `pnpm lint`            | Check formatting and lint with Biome.                      |
 | `pnpm test`            | Run the Vitest suite.                                      |
 | `pnpm test:coverage`   | Run tests with coverage (what CI runs).                    |
 | `pnpm test:watch`      | Watch mode.                                                |
 | `pnpm build:component` | Type check + build the npm library.                        |
 | `pnpm build:demo`      | Build the demo app only.                                   |
 | `pnpm build`           | Clean and build component + demo.                          |
-| `pnpm integrate`       | format:check → lint → test → build (CI mirror).            |
+| `pnpm integrate`       | lint → test → build (CI mirror).                           |
 
 ## CI/CD
 
 - **CI** (`continuous-integration.yml`): Runs on all PRs to `main` and
-  `workflow_dispatch`. Jobs: `format`, `lint`, `test` (with coverage artifact
-  and clover coverage delta comment), `build`, and `npm-dry-run` (validates the
-  npm publish would succeed). CI concurrency cancels in-progress runs. Uses the
+  `workflow_dispatch`. Jobs: `lint`, `test` (with coverage artifact and clover
+  coverage delta comment), `build`, and `npm-dry-run` (validates the npm publish
+  would succeed). CI concurrency cancels in-progress runs. Uses the
   `./.github/actions/setup` composite action with
   `pnpm install --frozen-lockfile`
 - **CD** (`continuous-deployment.yml`): Runs on push to `main` and

README.md

@@ -114,7 +114,7 @@ using either the `Sketch` type or the `P5CanvasInstance` type:
 import * as React from "react";
 import { P5Canvas, Sketch } from "@p5-wrapper/react";
 
-const sketch: Sketch = p5 => {
+const sketch: Sketch = (p5) => {
   p5.setup = () => p5.createCanvas(600, 400, p5.WEBGL);
 
   p5.draw = () => {
@@ -200,7 +200,7 @@ function sketch(p5) {
 
   p5.setup = () => p5.createCanvas(600, 400, p5.WEBGL);
 
-  p5.updateWithProps = props => {
+  p5.updateWithProps = (props) => {
     rotation = (props.rotation * Math.PI) / 180;
   };
 
@@ -220,7 +220,7 @@ export function App() {
 
   useEffect(() => {
     const interval = setInterval(
-      () => setRotation(rotation => rotation + 100),
+      () => setRotation((rotation) => rotation + 100),
       100
     );
 
@@ -245,12 +245,12 @@ type MySketchProps = SketchProps & {
   rotation: number;
 };
 
-const sketch: Sketch<MySketchProps> = p5 => {
+const sketch: Sketch<MySketchProps> = (p5) => {
   let rotation = 0;
 
   p5.setup = () => p5.createCanvas(600, 400, p5.WEBGL);
 
-  p5.updateWithProps = props => {
+  p5.updateWithProps = (props) => {
     rotation = (props.rotation * Math.PI) / 180;
   };
 
@@ -270,7 +270,7 @@ export function App() {
 
   useEffect(() => {
     const interval = setInterval(
-      () => setRotation(rotation => rotation + 100),
+      () => setRotation((rotation) => rotation + 100),
       100
     );
 
@@ -313,12 +313,12 @@ import React, { useCallback, useState } from "react";
 
 type MySketchProps = SketchProps & { rotation: number };
 
-const sketch: Sketch<MySketchProps> = p5 => {
+const sketch: Sketch<MySketchProps> = (p5) => {
   let rotation = 0;
 
   p5.setup = () => p5.createCanvas(600, 400, p5.WEBGL);
 
-  p5.updateWithProps = props => {
+  p5.updateWithProps = (props) => {
     rotation = (props.rotation * Math.PI) / 180;
   };
 
@@ -385,7 +385,7 @@ export function App() {
 
   useEffect(() => {
     const interval = setInterval(
-      () => setRotation(rotation => rotation + 100),
+      () => setRotation((rotation) => rotation + 100),
       100
     );
 
@@ -576,7 +576,7 @@ import React, { useEffect, useState } from "react";
 
 await import("p5/lib/addons/p5.sound");
 
-const sketch: Sketch = p5 => {
+const sketch: Sketch = (p5) => {
   let song: p5.SoundFile;
   let button: p5.Element;
 
@@ -688,13 +688,11 @@ public API in `src/main.tsx` backwards compatible. Commits follow the
 `fix:`, `chore:`, etc.) — emoji prefixes are only used by automated pull
 requests.
 
-The `typescript` dependency is pinned to `6.0.3` on purpose:
-[typescript-eslint](https://typescript-eslint.io) does not support TypeScript 7
-yet — the Go-based v7 is not feature compatible with the v6 API it builds on,
-and upstream support cannot land before TypeScript 7.1.x. It is tracked in
-[typescript-eslint#10940](https://github.com/typescript-eslint/typescript-eslint/issues/10940).
-Please do not widen the pin in pull requests — we wait for full feature parity
-before migrating to v7, no half measures.
+The `typescript` dependency is pinned to the latest `6.x.x` release on purpose:
+TypeScript 7 (Go-based) is not yet feature compatible with the JavaScript-based
+v6 API that the build toolchain builds on. Please do not bump past `6.x.x` or
+widen the pin in pull requests — we wait for full feature parity before
+migrating to v7, no half measures.
 
 #### AI-assisted contributions
 

biome.json

@@ -0,0 +1,95 @@
+{
+  "$schema": "./node_modules/@biomejs/biome/configuration_schema.json",
+  "vcs": {
+    "enabled": true,
+    "clientKind": "git",
+    "useIgnoreFile": true,
+    "defaultBranch": "main"
+  },
+  "files": {
+    "ignoreUnknown": true
+  },
+  "formatter": {
+    "enabled": true,
+    "indentStyle": "space",
+    "indentWidth": 2
+  },
+  "assist": {
+    "actions": {
+      "source": {
+        "organizeImports": "on"
+      }
+    }
+  },
+  "linter": {
+    "enabled": true,
+    "rules": {
+      "preset": "recommended",
+      "style": {
+        "useBlockStatements": "error",
+        "useImportType": "off"
+      }
+    }
+  },
+  "javascript": {
+    "formatter": {
+      "quoteStyle": "double",
+      "semicolons": "always",
+      "trailingCommas": "none"
+    }
+  },
+  "json": {
+    "formatter": {
+      "enabled": true,
+      "trailingCommas": "none"
+    }
+  },
+  "css": {
+    "formatter": {
+      "enabled": true
+    },
+    "parser": {
+      "tailwindDirectives": true
+    }
+  },
+  "markdown": {
+    "formatter": {
+      "enabled": true,
+      "proseWrap": "always"
+    },
+    "parser": {
+      "frontmatter": true
+    }
+  },
+  "yaml": {
+    "formatter": {
+      "enabled": true
+    }
+  },
+  "overrides": [
+    {
+      "includes": ["**/pnpm-lock.yaml"],
+      "formatter": {
+        "enabled": false
+      },
+      "linter": {
+        "enabled": false
+      },
+      "assist": {
+        "enabled": false
+      }
+    },
+    {
+      "includes": ["**/CLAUDE.md"],
+      "formatter": {
+        "enabled": false
+      },
+      "linter": {
+        "enabled": false
+      },
+      "assist": {
+        "enabled": false
+      }
+    }
+  ]
+}