feat: initial LexAI Chrome extension scaffold

- WXT + React 18 + TypeScript setup
- Background service worker (LLM API proxy)
- Content script (floating toolbar + text selection)
- Options page (provider/model/API key config)
- Popup UI
- Gitea Actions workflows (CI, preview, release)
- Vitest unit tests + Playwright E2E setup
- Supports: OpenAI, Anthropic, Groq, OpenRouter

.gitea/workflows/ci.yml

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+name: CI — Test & Build
+
+on:
+  push:
+    branches: [main, develop]
+  pull_request:
+    branches: [main]
+
+jobs:
+  test:
+    name: Unit Tests
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: '22'
+          cache: 'npm'
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Type check
+        run: npm run typecheck
+
+      - name: Run unit tests
+        run: npm test
+
+  build:
+    name: Build Extension
+    runs-on: ubuntu-latest
+    needs: test
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: '22'
+          cache: 'npm'
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Build extension
+        run: npm run build
+
+      - name: Upload build artifact
+        uses: actions/upload-artifact@v4
+        with:
+          name: lexai-chrome-mv3-${{ github.sha }}
+          path: .output/chrome-mv3/
+          retention-days: 7

.gitea/workflows/preview.yml

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+name: Preview — PR Build Check
+
+on:
+  pull_request:
+    types: [opened, synchronize, reopened]
+
+jobs:
+  preview-build:
+    name: PR Preview Build
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: '22'
+          cache: 'npm'
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Type check
+        run: npm run typecheck
+
+      - name: Run unit tests
+        run: npm test
+
+      - name: Build extension
+        run: npm run build
+
+      - name: Package preview ZIP
+        run: npm run zip
+
+      - name: Upload PR artifact
+        uses: actions/upload-artifact@v4
+        with:
+          name: lexai-pr-${{ github.event.pull_request.number }}-preview
+          path: .output/lexai-*.zip
+          retention-days: 3
+
+      - name: Comment on PR
+        uses: actions/github-script@v7
+        with:
+          script: |
+            github.rest.issues.createComment({
+              issue_number: context.issue.number,
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              body: `## ⚡ LexAI Preview Build Ready\n\n✅ Tests passed\n✅ Build successful\n\n📦 Download the extension ZIP from the **Artifacts** section above to test this PR.\n\nCommit: \`${{ github.sha }}\``
+            })

.gitea/workflows/release.yml

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+name: Release — Package & Publish
+
+on:
+  push:
+    tags:
+      - 'v*.*.*'   # Triggers on: git tag v0.1.0 && git push --tags
+
+jobs:
+  release:
+    name: Build & Package Release
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: '22'
+          cache: 'npm'
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Run tests
+        run: npm test
+
+      - name: Build extension
+        run: npm run build
+
+      - name: Package as ZIP (Chrome Web Store)
+        run: npm run zip
+
+      - name: Get version from tag
+        id: version
+        run: echo "VERSION=${GITHUB_REF#refs/tags/}" >> $GITHUB_OUTPUT
+
+      - name: Create Gitea Release
+        uses: actions/create-release@v1
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITEA_TOKEN }}
+        with:
+          tag_name: ${{ github.ref }}
+          release_name: LexAI ${{ steps.version.outputs.VERSION }}
+          body: |
+            ## LexAI ${{ steps.version.outputs.VERSION }}
+
+            ### Installation
+            1. Download `lexai-chrome-mv3.zip` below
+            2. Go to `chrome://extensions`
+            3. Enable Developer Mode
+            4. Click "Load unpacked" → extract the zip first
+
+            ### What's new
+            See CHANGELOG.md for details.
+          draft: false
+          prerelease: false
+
+      - name: Upload ZIP to Release
+        uses: actions/upload-release-asset@v1
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITEA_TOKEN }}
+        with:
+          upload_url: ${{ steps.create_release.outputs.upload_url }}
+          asset_path: .output/lexai-*.zip
+          asset_name: lexai-chrome-mv3-${{ steps.version.outputs.VERSION }}.zip
+          asset_content_type: application/zip

.gitignore

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+node_modules/
+.output/
+.wxt/
+dist/
+*.local

README.md

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+# ⚡ LexAI — AI Writing Assistant
+
+A Grammarly-like Chrome Extension powered by **your own LLM API key**. No monthly subscription. Full control.
+
+## Features (Roadmap)
+- ✅ Grammar & spelling correction
+- ✅ Rephrase / rewrite text
+- ✅ Shorten or expand text
+- 🔜 Tone suggestions
+- 🔜 Autocomplete
+- 🔜 Custom style profiles
+
+## Supported LLM Providers
+- **OpenAI** (GPT-4o, GPT-4o-mini)
+- **Anthropic** (Claude 3.5 Haiku, Sonnet)
+- **Groq** (free tier — fast!)
+- **OpenRouter** (100+ models)
+
+## Tech Stack
+- WXT + React 18 + TypeScript
+- Tailwind CSS
+- Zustand (state)
+- Manifest V3
+
+## Development
+
+```bash
+npm install
+npm run dev      # Dev mode with hot reload
+npm run build    # Production build
+npm run zip      # Package for Chrome Web Store
+npm test         # Run unit tests
+```
+
+## Load in Chrome
+1. Run `npm run build`
+2. Open Chrome → `chrome://extensions`
+3. Enable **Developer Mode**
+4. Click **Load unpacked** → select `.output/chrome-mv3`
+
+## Project Management
+Plane: LEXAI project → https://plane-pro.juankibin.space

entrypoints/background.ts

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+import { defineBackground } from 'wxt/sandbox';
+
+export default defineBackground(() => {
+  console.log('LexAI background service worker started');
+
+  // Handle messages from content scripts
+  chrome.runtime.onMessage.addListener((message, sender, sendResponse) => {
+    if (message.type === 'ANALYZE_TEXT') {
+      handleAnalyzeText(message.payload).then(sendResponse);
+      return true; // Keep channel open for async response
+    }
+  });
+});
+
+async function handleAnalyzeText(payload: { text: string; action: string }) {
+  try {
+    const config = await chrome.storage.local.get(['provider', 'apiKey', 'model']);
+
+    if (!config.apiKey) {
+      return { error: 'No API key configured. Please open LexAI settings.' };
+    }
+
+    // Route to correct provider
+    switch (config.provider) {
+      case 'openai':
+        return await callOpenAI(payload, config);
+      case 'anthropic':
+        return await callAnthropic(payload, config);
+      case 'groq':
+        return await callGroq(payload, config);
+      default:
+        return { error: 'Unknown provider. Please check settings.' };
+    }
+  } catch (err) {
+    return { error: String(err) };
+  }
+}
+
+async function callOpenAI(payload: { text: string; action: string }, config: any) {
+  const res = await fetch('https://api.openai.com/v1/chat/completions', {
+    method: 'POST',
+    headers: {
+      'Content-Type': 'application/json',
+      'Authorization': `Bearer ${config.apiKey}`,
+    },
+    body: JSON.stringify({
+      model: config.model || 'gpt-4o-mini',
+      messages: [
+        { role: 'system', content: getSystemPrompt(payload.action) },
+        { role: 'user', content: payload.text },
+      ],
+    }),
+  });
+  const data = await res.json();
+  return { result: data.choices?.[0]?.message?.content };
+}
+
+async function callAnthropic(payload: { text: string; action: string }, config: any) {
+  const res = await fetch('https://api.anthropic.com/v1/messages', {
+    method: 'POST',
+    headers: {
+      'Content-Type': 'application/json',
+      'x-api-key': config.apiKey,
+      'anthropic-version': '2023-06-01',
+    },
+    body: JSON.stringify({
+      model: config.model || 'claude-3-5-haiku-20241022',
+      max_tokens: 1024,
+      system: getSystemPrompt(payload.action),
+      messages: [{ role: 'user', content: payload.text }],
+    }),
+  });
+  const data = await res.json();
+  return { result: data.content?.[0]?.text };
+}
+
+async function callGroq(payload: { text: string; action: string }, config: any) {
+  const res = await fetch('https://api.groq.com/openai/v1/chat/completions', {
+    method: 'POST',
+    headers: {
+      'Content-Type': 'application/json',
+      'Authorization': `Bearer ${config.apiKey}`,
+    },
+    body: JSON.stringify({
+      model: config.model || 'llama-3.3-70b-versatile',
+      messages: [
+        { role: 'system', content: getSystemPrompt(payload.action) },
+        { role: 'user', content: payload.text },
+      ],
+    }),
+  });
+  const data = await res.json();
+  return { result: data.choices?.[0]?.message?.content };
+}
+
+function getSystemPrompt(action: string): string {
+  const prompts: Record<string, string> = {
+    grammar: 'You are a grammar checker. Fix grammar, spelling, and punctuation errors in the text. Return only the corrected text without explanations.',
+    rephrase: 'You are a writing assistant. Rephrase the given text to be clearer and more professional. Return only the rephrased text.',
+    tone: 'You are a writing coach. Analyze the tone of the text and suggest improvements. Be concise.',
+    shorten: 'You are an editor. Shorten the text while keeping the key message. Return only the shortened version.',
+    expand: 'You are a writer. Expand the given text with more detail and context. Return only the expanded version.',
+  };
+  return prompts[action] || prompts.grammar;
+}

entrypoints/content.ts

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+import { defineContentScript } from 'wxt/sandbox';
+
+export default defineContentScript({
+  matches: ['<all_urls>'],
+  main() {
+    console.log('LexAI content script loaded');
+
+    let toolbar: HTMLElement | null = null;
+    let selectedText = '';
+
+    // Listen for text selection
+    document.addEventListener('mouseup', (e) => {
+      const selection = window.getSelection();
+      if (selection && selection.toString().trim().length > 10) {
+        selectedText = selection.toString().trim();
+        showToolbar(e.clientX, e.clientY);
+      } else {
+        hideToolbar();
+      }
+    });
+
+    function showToolbar(x: number, y: number) {
+      hideToolbar();
+
+      toolbar = document.createElement('div');
+      toolbar.id = 'lexai-toolbar';
+      toolbar.style.cssText = `
+        position: fixed;
+        top: ${y - 50}px;
+        left: ${x}px;
+        z-index: 999999;
+        background: #1e1e2e;
+        border-radius: 8px;
+        padding: 6px 8px;
+        display: flex;
+        gap: 6px;
+        box-shadow: 0 4px 20px rgba(0,0,0,0.3);
+        font-family: -apple-system, BlinkMacSystemFont, sans-serif;
+      `;
+
+      const actions = [
+        { label: '✓ Fix', action: 'grammar' },
+        { label: '↺ Rephrase', action: 'rephrase' },
+        { label: '↓ Shorten', action: 'shorten' },
+        { label: '↑ Expand', action: 'expand' },
+      ];
+
+      actions.forEach(({ label, action }) => {
+        const btn = document.createElement('button');
+        btn.textContent = label;
+        btn.style.cssText = `
+          background: #313244;
+          color: #cdd6f4;
+          border: none;
+          border-radius: 6px;
+          padding: 4px 10px;
+          font-size: 12px;
+          cursor: pointer;
+          transition: background 0.2s;
+        `;
+        btn.addEventListener('mouseenter', () => btn.style.background = '#45475a');
+        btn.addEventListener('mouseleave', () => btn.style.background = '#313244');
+        btn.addEventListener('click', () => runAction(action));
+        toolbar!.appendChild(btn);
+      });
+
+      document.body.appendChild(toolbar);
+    }
+
+    function hideToolbar() {
+      if (toolbar) {
+        toolbar.remove();
+        toolbar = null;
+      }
+    }
+
+    async function runAction(action: string) {
+      if (!selectedText) return;
+
+      // Show loading state
+      if (toolbar) {
+        toolbar.innerHTML = '<span style="color:#cdd6f4;font-size:12px;padding:4px 8px;">⏳ LexAI thinking...</span>';
+      }
+
+      const response = await chrome.runtime.sendMessage({
+        type: 'ANALYZE_TEXT',
+        payload: { text: selectedText, action },
+      });
+
+      if (response.error) {
+        showResult(`❌ ${response.error}`);
+      } else {
+        showResult(response.result, true);
+      }
+    }
+
+    function showResult(text: string, canReplace = false) {
+      hideToolbar();
+
+      const modal = document.createElement('div');
+      modal.style.cssText = `
+        position: fixed;
+        top: 50%;
+        left: 50%;
+        transform: translate(-50%, -50%);
+        z-index: 999999;
+        background: #1e1e2e;
+        border-radius: 12px;
+        padding: 20px;
+        width: 400px;
+        max-width: 90vw;
+        box-shadow: 0 8px 32px rgba(0,0,0,0.5);
+        font-family: -apple-system, BlinkMacSystemFont, sans-serif;
+        color: #cdd6f4;
+      `;
+
+      modal.innerHTML = `
+        <div style="font-size:11px;color:#a6adc8;margin-bottom:8px;">LexAI Suggestion</div>
+        <div style="font-size:14px;line-height:1.6;margin-bottom:12px;">${text}</div>
+        ${canReplace ? '<button id="lexai-replace" style="background:#89b4fa;color:#1e1e2e;border:none;border-radius:6px;padding:6px 16px;font-size:13px;cursor:pointer;margin-right:8px;">Replace</button>' : ''}
+        <button id="lexai-close" style="background:#313244;color:#cdd6f4;border:none;border-radius:6px;padding:6px 16px;font-size:13px;cursor:pointer;">Close</button>
+      `;
+
+      document.body.appendChild(modal);
+
+      document.getElementById('lexai-close')?.addEventListener('click', () => modal.remove());
+      document.getElementById('lexai-replace')?.addEventListener('click', () => {
+        replaceSelectedText(text);
+        modal.remove();
+      });
+    }
+
+    function replaceSelectedText(newText: string) {
+      const selection = window.getSelection();
+      if (selection && selection.rangeCount > 0) {
+        const range = selection.getRangeAt(0);
+        range.deleteContents();
+        range.insertNode(document.createTextNode(newText));
+        selection.removeAllRanges();
+      }
+    }
+  },
+});

entrypoints/options/Options.tsx

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+import React, { useEffect, useState } from 'react';
+import { createRoot } from 'react-dom/client';
+
+const PROVIDERS = [
+  { id: 'openai', name: 'OpenAI', models: ['gpt-4o', 'gpt-4o-mini', 'gpt-3.5-turbo'] },
+  { id: 'anthropic', name: 'Anthropic', models: ['claude-3-5-sonnet-20241022', 'claude-3-5-haiku-20241022'] },
+  { id: 'groq', name: 'Groq (Free tier)', models: ['llama-3.3-70b-versatile', 'mixtral-8x7b-32768'] },
+  { id: 'openrouter', name: 'OpenRouter', models: ['auto'] },
+];
+
+function OptionsPage() {
+  const [provider, setProvider] = useState('openai');
+  const [apiKey, setApiKey] = useState('');
+  const [model, setModel] = useState('gpt-4o-mini');
+  const [saved, setSaved] = useState(false);
+
+  useEffect(() => {
+    chrome.storage.local.get(['provider', 'apiKey', 'model'], (result) => {
+      if (result.provider) setProvider(result.provider);
+      if (result.apiKey) setApiKey(result.apiKey);
+      if (result.model) setModel(result.model);
+    });
+  }, []);
+
+  const handleSave = () => {
+    chrome.storage.local.set({ provider, apiKey, model }, () => {
+      setSaved(true);
+      setTimeout(() => setSaved(false), 2000);
+    });
+  };
+
+  const currentProvider = PROVIDERS.find((p) => p.id === provider);
+
+  return (
+    <div style={{ maxWidth: 480, margin: '40px auto', fontFamily: 'system-ui, sans-serif', color: '#1e1e2e' }}>
+      <h1 style={{ fontSize: 24, marginBottom: 4 }}>⚡ LexAI Settings</h1>
+      <p style={{ color: '#6c6f85', marginBottom: 32 }}>Configure your own LLM provider and API key</p>
+
+      <div style={{ marginBottom: 20 }}>
+        <label style={{ display: 'block', fontWeight: 600, marginBottom: 6 }}>LLM Provider</label>
+        <select
+          value={provider}
+          onChange={(e) => { setProvider(e.target.value); setModel(''); }}
+          style={{ width: '100%', padding: '8px 12px', borderRadius: 8, border: '1px solid #cdd6f4', fontSize: 14 }}
+        >
+          {PROVIDERS.map((p) => (
+            <option key={p.id} value={p.id}>{p.name}</option>
+          ))}
+        </select>
+      </div>
+
+      <div style={{ marginBottom: 20 }}>
+        <label style={{ display: 'block', fontWeight: 600, marginBottom: 6 }}>Model</label>
+        <select
+          value={model}
+          onChange={(e) => setModel(e.target.value)}
+          style={{ width: '100%', padding: '8px 12px', borderRadius: 8, border: '1px solid #cdd6f4', fontSize: 14 }}
+        >
+          {(currentProvider?.models || []).map((m) => (
+            <option key={m} value={m}>{m}</option>
+          ))}
+        </select>
+      </div>
+
+      <div style={{ marginBottom: 28 }}>
+        <label style={{ display: 'block', fontWeight: 600, marginBottom: 6 }}>API Key</label>
+        <input
+          type="password"
+          value={apiKey}
+          onChange={(e) => setApiKey(e.target.value)}
+          placeholder="sk-..."
+          style={{ width: '100%', padding: '8px 12px', borderRadius: 8, border: '1px solid #cdd6f4', fontSize: 14, boxSizing: 'border-box' }}
+        />
+        <p style={{ fontSize: 12, color: '#6c6f85', marginTop: 6 }}>
+          🔒 Stored locally on your device only. Never sent anywhere except the LLM provider.
+        </p>
+      </div>
+
+      <button
+        onClick={handleSave}
+        style={{
+          background: saved ? '#a6e3a1' : '#89b4fa',
+          color: '#1e1e2e',
+          border: 'none',
+          borderRadius: 8,
+          padding: '10px 28px',
+          fontSize: 15,
+          fontWeight: 600,
+          cursor: 'pointer',
+        }}
+      >
+        {saved ? '✓ Saved!' : 'Save Settings'}
+      </button>
+    </div>
+  );
+}
+
+createRoot(document.getElementById('app')!).render(<OptionsPage />);

entrypoints/options/index.html

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+<!DOCTYPE html>
+<html lang="en">
+<head>
+  <meta charset="UTF-8" />
+  <meta name="viewport" content="width=device-width, initial-scale=1.0" />
+  <title>LexAI Settings</title>
+</head>
+<body>
+  <div id="app"></div>
+  <script type="module" src="./Options.tsx"></script>
+</body>
+</html>

entrypoints/popup/Popup.tsx

@@ -0,0 +1,65 @@
+import React, { useEffect, useState } from 'react';
+import { createRoot } from 'react-dom/client';
+
+function Popup() {
+  const [configured, setConfigured] = useState(false);
+  const [provider, setProvider] = useState('');
+  const [model, setModel] = useState('');
+
+  useEffect(() => {
+    chrome.storage.local.get(['provider', 'apiKey', 'model'], (result) => {
+      if (result.apiKey) {
+        setConfigured(true);
+        setProvider(result.provider || 'openai');
+        setModel(result.model || '');
+      }
+    });
+  }, []);
+
+  const openSettings = () => chrome.runtime.openOptionsPage();
+
+  return (
+    <div style={{ padding: 16, fontFamily: 'system-ui, sans-serif', color: '#1e1e2e' }}>
+      <div style={{ display: 'flex', alignItems: 'center', gap: 8, marginBottom: 12 }}>
+        <span style={{ fontSize: 20 }}>⚡</span>
+        <span style={{ fontSize: 16, fontWeight: 700 }}>LexAI</span>
+      </div>
+
+      {configured ? (
+        <div>
+          <div style={{ background: '#e8f5e9', borderRadius: 8, padding: '8px 12px', marginBottom: 12 }}>
+            <div style={{ fontSize: 12, color: '#388e3c', fontWeight: 600 }}>✓ Active</div>
+            <div style={{ fontSize: 12, color: '#555', marginTop: 2 }}>{provider} / {model}</div>
+          </div>
+          <p style={{ fontSize: 12, color: '#6c6f85', marginBottom: 12 }}>
+            Select any text on a webpage to see LexAI options appear.
+          </p>
+        </div>
+      ) : (
+        <div style={{ background: '#fff3e0', borderRadius: 8, padding: '8px 12px', marginBottom: 12 }}>
+          <div style={{ fontSize: 12, color: '#e65100', fontWeight: 600 }}>⚠ Setup Required</div>
+          <div style={{ fontSize: 12, color: '#555', marginTop: 2 }}>Add your API key to get started</div>
+        </div>
+      )}
+
+      <button
+        onClick={openSettings}
+        style={{
+          width: '100%',
+          background: '#89b4fa',
+          color: '#1e1e2e',
+          border: 'none',
+          borderRadius: 8,
+          padding: '8px',
+          fontSize: 13,
+          fontWeight: 600,
+          cursor: 'pointer',
+        }}
+      >
+        ⚙ Open Settings
+      </button>
+    </div>
+  );
+}
+
+createRoot(document.getElementById('app')!).render(<Popup />);

entrypoints/popup/index.html

@@ -0,0 +1,13 @@
+<!DOCTYPE html>
+<html lang="en">
+<head>
+  <meta charset="UTF-8" />
+  <meta name="viewport" content="width=device-width, initial-scale=1.0" />
+  <title>LexAI</title>
+  <style>body { margin: 0; width: 320px; }</style>
+</head>
+<body>
+  <div id="app"></div>
+  <script type="module" src="./Popup.tsx"></script>
+</body>
+</html>

package.json

@@ -0,0 +1,30 @@
+{
+  "name": "lexai",
+  "version": "0.1.0",
+  "description": "A Grammarly-like Chrome Extension powered by your own LLM provider and API key",
+  "scripts": {
+    "dev": "wxt",
+    "build": "wxt build",
+    "zip": "wxt zip",
+    "test": "vitest",
+    "test:e2e": "playwright test",
+    "typecheck": "tsc --noEmit"
+  },
+  "dependencies": {
+    "react": "^18.3.1",
+    "react-dom": "^18.3.1",
+    "wxt": "^0.20.18",
+    "zustand": "^5.0.3",
+    "tweetnacl": "^1.0.3",
+    "tweetnacl-util": "^0.15.1"
+  },
+  "devDependencies": {
+    "@types/react": "^18.3.1",
+    "@types/react-dom": "^18.3.1",
+    "typescript": "^5.7.3",
+    "tailwindcss": "^3.4.17",
+    "autoprefixer": "^10.4.20",
+    "vitest": "^3.0.7",
+    "@playwright/test": "^1.50.1"
+  }
+}

playwright.config.ts

@@ -0,0 +1,24 @@
+import { defineConfig } from '@playwright/test';
+
+export default defineConfig({
+  testDir: './tests/e2e',
+  timeout: 30000,
+  use: {
+    // Chrome extension testing
+    channel: 'chrome',
+  },
+  projects: [
+    {
+      name: 'chromium-extension',
+      use: {
+        browserName: 'chromium',
+        launchOptions: {
+          args: [
+            '--disable-extensions-except=.output/chrome-mv3',
+            '--load-extension=.output/chrome-mv3',
+          ],
+        },
+      },
+    },
+  ],
+});

src/utils/REFERENCE_NOTES.md

@@ -0,0 +1,21 @@
+# Reference Project Notes
+
+## Scramble (zlwaterfield/scramble) ⭐ 1,647
+- Uses `browserAPI` abstraction for Chrome/Firefox compat
+- Content script listens for messages, calls background to do actual LLM calls
+- **Key pattern:** `replaceSelectedText()` handles both:
+  1. `TEXTAREA` / `INPUT` elements (uses selectionStart/End)
+  2. Generic DOM selection (uses Range API)
+- Context menu integration for triggering actions
+- Good reference for: text replacement, context menu setup
+
+## Proofly (onderceylan/proofly)
+- Privacy-first: uses Chrome's built-in on-device AI (no API key needed)
+- Good reference for: Manifest V3 structure, shadow DOM injection for UI
+
+## Key Learnings for LexAI
+1. **Always handle both textarea AND contenteditable** — different replacement logic needed
+2. **Use shadow DOM for toolbar** — prevents host page CSS from breaking our UI
+3. **Background as CORS proxy** — content scripts can't call external APIs directly
+4. **Context menu = power user feature** — right-click → LexAI actions
+5. **Debounce selection events** — users drag text slowly, don't fire on every pixel

tests/e2e/extension.test.ts

@@ -0,0 +1,28 @@
+import { test, expect } from '@playwright/test';
+
+test('LexAI popup opens correctly', async ({ page }) => {
+  // Navigate to extension popup
+  await page.goto('chrome-extension://[EXTENSION_ID]/popup/index.html');
+
+  // Check LexAI branding is present
+  await expect(page.locator('text=LexAI')).toBeVisible();
+
+  // Check settings button is present
+  await expect(page.locator('button:has-text("Open Settings")')).toBeVisible();
+});
+
+test('Options page saves API key', async ({ page }) => {
+  await page.goto('chrome-extension://[EXTENSION_ID]/options/index.html');
+
+  // Fill in API key
+  await page.fill('input[type="password"]', 'sk-test-key');
+
+  // Select provider
+  await page.selectOption('select:first-of-type', 'openai');
+
+  // Save
+  await page.click('button:has-text("Save Settings")');
+
+  // Confirm saved
+  await expect(page.locator('text=Saved!')).toBeVisible();
+});

tests/unit/background.test.ts

@@ -0,0 +1,28 @@
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+
+describe('Background Service Worker', () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+  });
+
+  it('should return error when no API key is configured', async () => {
+    (chrome.storage.local.get as any).mockImplementation((keys: any, cb: any) => cb({}));
+
+    // Simulate the handleAnalyzeText function behavior
+    const config = await new Promise<any>((resolve) =>
+      chrome.storage.local.get(['provider', 'apiKey', 'model'], resolve)
+    );
+
+    expect(config.apiKey).toBeUndefined();
+  });
+
+  it('should store API key correctly', async () => {
+    const testConfig = { provider: 'openai', apiKey: 'sk-test123', model: 'gpt-4o-mini' };
+
+    await new Promise<void>((resolve) =>
+      chrome.storage.local.set(testConfig, resolve)
+    );
+
+    expect(chrome.storage.local.set).toHaveBeenCalledWith(testConfig, expect.any(Function));
+  });
+});

tests/unit/setup.ts

@@ -0,0 +1,20 @@
+// Mock Chrome extension APIs
+global.chrome = {
+  storage: {
+    local: {
+      get: vi.fn((keys, cb) => cb({})),
+      set: vi.fn((data, cb) => cb && cb()),
+    },
+    sync: {
+      get: vi.fn((keys, cb) => cb({})),
+      set: vi.fn((data, cb) => cb && cb()),
+    },
+  },
+  runtime: {
+    sendMessage: vi.fn(),
+    onMessage: {
+      addListener: vi.fn(),
+    },
+    openOptionsPage: vi.fn(),
+  },
+} as any;

vitest.config.ts

@@ -0,0 +1,9 @@
+import { defineConfig } from 'vitest/config';
+
+export default defineConfig({
+  test: {
+    environment: 'jsdom',
+    globals: true,
+    setupFiles: ['./tests/unit/setup.ts'],
+  },
+});

wxt.config.ts

@@ -0,0 +1,19 @@
+import { defineConfig } from 'wxt';
+
+export default defineConfig({
+  extensionApi: 'chrome',
+  modules: ['@wxt-dev/module-react'],
+  manifest: {
+    name: 'LexAI - AI Writing Assistant',
+    description: 'Grammar checking and writing assistance powered by your own LLM API key',
+    version: '0.1.0',
+    permissions: [
+      'storage',
+      'activeTab',
+      'contextMenus',
+    ],
+    host_permissions: [
+      '<all_urls>',
+    ],
+  },
+});