feat: replace ESLint with Biome and add Lefthook for git hooks

.biomeignore

@@ -0,0 +1,8 @@
+node_modules/
+dist/
+.turbo/
+coverage/
+*.lock
+bun.lock
+.changeset/
+docs_archive/

.changeset/config.json

@@ -8,4 +8,4 @@
   "baseBranch": "main",
   "updateInternalDependencies": "patch",
   "ignore": []
-}
+}

.github/actions/setup-bun-and-deps/action.yml

@@ -1,26 +1,26 @@
-name: 'Setup Bun and Dependencies'
-description: 'Setup Bun runtime, install dependencies, and optionally run lint/test/build'
+name: "Setup Bun and Dependencies"
+description: "Setup Bun runtime, install dependencies, and optionally run lint/test/build"
 
 inputs:
   bun-version:
-    description: 'Version of Bun to install'
+    description: "Version of Bun to install"
     required: true
-    default: '1.2.21'
+    default: "1.2.21"
   run-lint:
-    description: 'Whether to run lint'
+    description: "Whether to run lint"
     required: false
-    default: 'true'
+    default: "true"
   run-test:
-    description: 'Whether to run test'
+    description: "Whether to run test"
     required: false
-    default: 'true'
+    default: "true"
   run-build:
-    description: 'Whether to run build'
+    description: "Whether to run build"
     required: false
-    default: 'true'
+    default: "true"
 
 runs:
-  using: 'composite'
+  using: "composite"
   steps:
     - name: Setup Bun
       uses: oven-sh/setup-bun@735343b667d3e6f658f44d0eca948eb6282f2b76 # v2
@@ -31,9 +31,14 @@ runs:
       run: bun install --frozen-lockfile
       shell: bash
 
-    - name: Lint
+    - name: Check Format
       if: inputs.run-lint == 'true'
-      run: bun run lint
+      run: bun run check:ci
+      shell: bash
+
+    - name: Lint Markdown
+      if: inputs.run-lint == 'true'
+      run: bun run lint:md
       shell: bash
 
     - name: Test
@@ -44,4 +49,4 @@ runs:
     - name: Build
       if: inputs.run-build == 'true'
       run: bun run build
-      shell: bash
+      shell: bash

.markdownlint-cli2.yaml

@@ -0,0 +1,23 @@
+config:
+  default: true
+  MD013: false # Line length
+  MD033: false # Allow inline HTML
+  MD041: false # First line in a file should be a top-level heading
+  MD024:
+    siblings_only: true # Allow duplicate headings if not siblings
+  MD025: false # Multiple top-level headings
+  line-length: false
+
+ignores:
+  - node_modules/**
+  - "**/node_modules/**"
+  - dist/**
+  - "**/dist/**"
+  - .turbo/**
+  - "**/.turbo/**"
+  - coverage/**
+  - "**/coverage/**"
+  - "**/*.lock"
+  - "**/bun.lock"
+  - .changeset/**
+  - docs_archive/**

.markdownlint.json

@@ -3,4 +3,4 @@
   "MD013": false,
   "MD033": false,
   "MD041": false
-}
+}

.prettierignore

@@ -0,0 +1,19 @@
+# Prettier should only handle YAML and Markdown files
+# TypeScript/JavaScript files are handled by Biome/Ultracite
+
+*.ts
+*.tsx
+*.js
+*.jsx
+*.json
+*.jsonc
+
+# Standard ignores
+node_modules/
+dist/
+build/
+coverage/
+.turbo/
+*.lock
+bun.lock
+.changeset/

.prettierrc

@@ -1,9 +1,19 @@
 {
   "semi": true,
   "singleQuote": true,
-  "trailingComma": "all",
-  "printWidth": 100,
   "tabWidth": 2,
   "useTabs": false,
-  "endOfLine": "lf"
+  "trailingComma": "es5",
+  "bracketSpacing": true,
+  "arrowParens": "always",
+  "printWidth": 100,
+  "endOfLine": "lf",
+  "overrides": [
+    {
+      "files": ["*.yml", "*.yaml"],
+      "options": {
+        "singleQuote": false
+      }
+    }
+  ]
 }

AGENTS.md

@@ -160,4 +160,4 @@ AI agents must consult these documents regularly:
 - `@docs/agentic/`: Agentic development coordination and agent-specific guides
 - `@docs/agentic/jules/`: Google Jules integration guides and prompts
 
-This structured approach ensures AI agents can efficiently navigate, understand, and contribute to the Mixdown codebase while maintaining consistency and quality.
+This structured approach ensures AI agents can efficiently navigate, understand, and contribute to the Mixdown codebase while maintaining consistency and quality.

CHANGELOG.md

@@ -1,7 +1,18 @@
+## [0.1.0] - 2025-09-01
+
 ### Added
+
 - Added `.mix.md` file extension for source rules files to improve discoverability, search capabilities, and IDE support
 
 ### Changed
+
+- Replaced ESLint with Biome/Ultracite for linting/formatting
+- Added Lefthook-managed git hooks
+- Configured markdownlint-cli2 for Markdown formatting
+- Updated package.json scripts and CI workflow to new lint commands
+- Converted parse/lint APIs from async to sync
+- Introduced Frontmatter type and updated frontmatter.rulesets structure
+- Updated tests to use runRulesetsV0 and new destinations model
 - Updated terminology throughout the documentation:
   - "Mix files" → "Source rules"
   - "Target" → "Destination"

README.md

@@ -1,6 +1,6 @@
 # 📏 Rulesets: A Compiler for AI Rules Files
 
-> **🚀 v0 Release Now Available!** The initial implementation of Rulesets is ready for testing. See [Installation](#installation) to get started.
+> **🚀 v0 Release Now Available!** The initial implementation of Rulesets is ready for testing. See [CLI Installation](#cli-installation) to get started.
 
 Rulesets simplifies rules management for tools like Cursor, Claude Code, Codex, etc. With Rulesets, you author rules (called "source rules") in previewable Markdown and compile them into compiled rules for each destination (`.cursor/rules.mdc`, `./CLAUDE.md`, `.roo/rules.md`, and more). Think of it as **Terraform for AI rules**: write once, compile for many destinations, your agents, no matter the tool, on the (literal) same page.
 
@@ -151,7 +151,8 @@ async function main() {
 main();
 ```
 
-### 3. Find your compiled rules at:
+### 3. Find your compiled rules at
+
 - `.cursor/rules/standards.mdc` (for Cursor)
 - `.windsurf/rules/standards.md` (for Windsurf)
 
@@ -231,4 +232,4 @@ Please see our general contributing guidelines for more details.
 ## References
 
 - `docs/project/OVERVIEW.md` – Full Mixdown notation specification.
-- `docs/architecture/DECISIONS.md` – Design rationale & deep-dive.
+- `docs/architecture/DECISIONS.md` – Design rationale & deep-dive.

biome.json

@@ -0,0 +1,50 @@
+{
+  "$schema": "https://biomejs.dev/schemas/2.2.2/schema.json",
+  "extends": ["ultracite"],
+  "javascript": {
+    "globals": ["Bun"]
+  },
+  "json": {
+    "parser": {
+      "allowComments": true,
+      "allowTrailingCommas": true
+    }
+  },
+  "files": {
+    "ignoreUnknown": true,
+    "includes": ["**/*.{js,ts,jsx,tsx,json,jsonc}"]
+  },
+  "vcs": {
+    "enabled": true,
+    "clientKind": "git",
+    "useIgnoreFile": true
+  },
+  "linter": {
+    "rules": {
+      "style": {
+        "noParameterAssign": "off",
+        "noNonNullAssertion": "off"
+      },
+      "complexity": {
+        "noBannedTypes": "off",
+        "noExcessiveCognitiveComplexity": "off"
+      },
+      "suspicious": {
+        "noExplicitAny": "off",
+        "noArrayIndexKey": "off",
+        "noEmptyBlockStatements": "off"
+      },
+      "performance": {
+        "noBarrelFile": "off"
+      },
+      "nursery": {
+        "noUnnecessaryConditions": "off"
+      }
+    }
+  },
+  "formatter": {
+    "indentStyle": "space",
+    "indentWidth": 2,
+    "lineWidth": 100
+  }
+}