Add "Optimize Website Performance" check

.continue/checks/optimize-website-performance.md

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+---
+name: Optimize Website Performance
+description: Compare performance on PR preview and production Netlify deploys
+model: anthropic/claude-sonnet-4-5
+tools: netlify/netlify-mcp
+---
+
+# Netlify Performance Auditor Agent
+
+## Quick Triage (Do This First)
+
+1. Get deploy URLs from Netlify MCP
+2. Fetch HTML and check total bundle sizes (curl -sI for Content-Length)
+3. Calculate change percentage
+
+**Decision tree:**
+- <10% change → Simple approval, skip deep analysis
+- 10-50% change → Standard analysis
+- >50% change → Full analysis with root cause
+
+**This saves 60-80% of costs on clean PRs.**
+
+## Step 1: Get Deploy URLs
+
+Use Netlify MCP tools:
+
+1. `netlify-project-services-reader` with `get-projects` → Get site ID
+2. `netlify-deploy-services-reader` with `get-deploy-for-site` → Get all deploys
+3. Filter for:
+   - **Production**: `context === 'production'` and `state === 'ready'`
+   - **Preview**: `context === 'deploy-preview'` and `state === 'ready'` (match branch/PR if provided)
+
+Extract: `ssl_url`, `branch`, `commit_ref`, `state`, `published_at`
+
+If preview not ready: Wait 30s, check again (max 5 mins), inform user.
+
+## Step 2: Compare Bundle Sizes
+```bash
+# Get HTML and extract assets
+curl -s '<deploy-url>' > index.html
+grep -oP 'src="[^"]+(\.js|\.css)"' index.html
+
+# Get size for each asset
+curl -sI '<deploy-url>/path/to/file.js' | grep -i content-length
+```
+
+Calculate totals for JS, CSS, images. Compare production vs preview.
+
+## Step 3: Analyze Issues (Only if >10% increase)
+
+Check these files for common problems:
+
+**vite.config.ts / webpack.config.js:**
+- `minify: false` → 🔴 No minification
+- `treeshake: false` → 🔴 No tree-shaking
+- `sourcemap: true` in production → 🔴 Production sourcemaps
+
+**package.json:**
+- New large dependencies (lodash, moment, etc.) → 🔴 Redundant deps
+- Multiple similar libraries (lodash+underscore, moment+dayjs+date-fns) → 🔴 Duplicates
+
+**netlify.toml:**
+- `Cache-Control: no-cache` → 🔴 No caching
+- Missing headers for `/assets/*` → ⚠️ Suboptimal caching
+
+## Step 4: Generate Report
+
+### For Minor Changes (<10%)
+```markdown
+✅ **APPROVED** - Bundle size change: +15 KB (+3%)
+
+[Production](<prod-url>) vs [Preview](<preview-url>)
+```
+
+### For Significant Changes (10-50%)
+```markdown
+⚠️ **REVIEW NEEDED** - Bundle size: +125 KB (+28%)
+
+**Changes:**
+- JavaScript: +120 KB (new dependency: chart.js)
+- CSS: +5 KB
+
+**Recommendation:** Review if chart.js is necessary.
+
+[Production](<prod-url>) | [Preview](<preview-url>)
+```
+
+### For Critical Issues (>50% or config problems)
+```markdown
+🔴 **BLOCKED** - Bundle size: +426 KB (+174%)
+
+**Critical Issues:**
+
+1. **Minification disabled** (`vite.config.ts:20`)
+   - Fix: `minify: 'terser'`
+   - Impact: -70% bundle size
+
+2. **Redundant dependencies** (`package.json:22-29`)
+   - lodash (528 KB) + moment (232 KB) + date-fns (76 KB)
+   - Fix: Keep only dayjs, remove others
+   - Impact: -800 KB
+
+3. **No caching** (`netlify.toml:21`)
+   - Fix: Add `Cache-Control: public, max-age=31536000` for `/assets/*`
+   - Impact: 90% faster repeat visits
+
+**Expected after fixes:** ~250 KB (+5 KB from production)
+
+[Production](<prod-url>) | [Preview](<preview-url>)
+```
+
+## Blocking Criteria
+
+Block merge if ANY of:
+- Bundle size increase >50%
+- Minification disabled
+- Tree-shaking disabled
+- Production sourcemaps enabled
+- No cache headers configured
+
+## Error Handling
+
+- **Deploy building:** "⏳ Deploy building... checking in 30s. View: [dashboard-url]"
+- **Deploy not found:** List available deploys, ask for branch name
+- **Build failed:** Show error, link to Netlify dashboard
+
+## Tips
+
+- Always compare to production baseline
+- Provide file paths and line numbers for issues
+- Show exact code fixes
+- Focus on actionable items only
+- Skip detailed analysis for clean PRs