Add frontend code coverage via Istanbul instrumentation + Playwright

- Install nyc for Istanbul instrumentation
- Add scripts/instrument-frontend.sh to instrument public/*.js
- Add scripts/collect-frontend-coverage.js to extract window.__coverage__
- Add scripts/combined-coverage.sh for combined server+frontend coverage
- Make server.js serve public-instrumented/ when COVERAGE=1 is set
- Add test:full-coverage npm script
- Add public-instrumented/ and .nyc_output/ to .gitignore

scripts/collect-frontend-coverage.js

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+// After Playwright tests, this script:
+// 1. Connects to the running test server
+// 2. Extracts window.__coverage__ from the browser
+// 3. Writes it to .nyc_output/ for merging
+
+const { chromium } = require('playwright');
+const fs = require('fs');
+const path = require('path');
+
+async function collectCoverage() {
+  const browser = await chromium.launch({
+    executablePath: process.env.CHROMIUM_PATH || '/usr/bin/chromium',
+    args: ['--no-sandbox'],
+    headless: true
+  });
+  const page = await browser.newPage();
+  const BASE = process.env.BASE_URL || 'http://localhost:13581';
+
+  // Visit every major page to exercise the code
+  const pages = ['#/home', '#/nodes', '#/map', '#/packets', '#/channels', '#/analytics', '#/live', '#/traces', '#/observers'];
+  for (const hash of pages) {
+    await page.goto(`${BASE}/${hash}`, { waitUntil: 'networkidle', timeout: 15000 }).catch(() => {});
+    await page.waitForTimeout(2000);
+  }
+
+  // Exercise some interactions
+  try {
+    await page.click('#customizeToggle');
+    await page.waitForTimeout(1000);
+  } catch {}
+
+  // Extract coverage
+  const coverage = await page.evaluate(() => window.__coverage__);
+  await browser.close();
+
+  if (coverage) {
+    const outDir = path.join(__dirname, '..', '.nyc_output');
+    if (!fs.existsSync(outDir)) fs.mkdirSync(outDir, { recursive: true });
+    fs.writeFileSync(path.join(outDir, 'frontend-coverage.json'), JSON.stringify(coverage));
+    console.log('Frontend coverage collected: ' + Object.keys(coverage).length + ' files');
+  } else {
+    console.log('WARNING: No __coverage__ object found — instrumentation may have failed');
+  }
+}
+
+collectCoverage().catch(e => { console.error(e); process.exit(1); });

scripts/combined-coverage.sh

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+#!/bin/sh
+# Run server-side tests with c8, then frontend coverage with nyc
+set -e
+
+# 1. Server-side coverage (existing)
+npx c8 --reporter=json --reports-dir=.nyc_output node tools/e2e-test.js
+
+# 2. Instrument frontend
+sh scripts/instrument-frontend.sh
+
+# 3. Start instrumented server
+COVERAGE=1 PORT=13581 node server.js &
+SERVER_PID=$!
+sleep 5
+
+# 4. Run Playwright tests (exercises frontend code)
+BASE_URL=http://localhost:13581 node test-e2e-playwright.js || true
+
+# 5. Collect browser coverage
+BASE_URL=http://localhost:13581 node scripts/collect-frontend-coverage.js
+
+# 6. Kill server
+kill $SERVER_PID 2>/dev/null || true
+
+# 7. Generate combined report
+npx nyc report --reporter=text-summary --reporter=text

scripts/instrument-frontend.sh

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+#!/bin/sh
+# Instrument frontend JS for coverage tracking
+rm -rf public-instrumented
+npx nyc instrument public/ public-instrumented/ --compact=false
+# Copy non-JS files (CSS, HTML, images) as-is
+cp public/*.css public-instrumented/ 2>/dev/null
+cp public/*.html public-instrumented/ 2>/dev/null
+cp public/*.svg public-instrumented/ 2>/dev/null
+cp public/*.png public-instrumented/ 2>/dev/null
+echo "Frontend instrumented successfully"