feat: add gzip toggle and cache mode (normal / no-cache / bust)

- Cache-mode selector: Normal, No-cache headers, Cache-bust URL+headers
- Cache-bust appends random ?_cb= per iteration to bypass CDN/proxy
- gzip toggle: on = k6 default (Accept-Encoding: gzip/br), off = identity
- Both options stored in DB with non-destructive migration
- History items show cache-mode and gzip pills
- Schema migration handles existing DBs gracefully

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/server.js

@@ -25,6 +25,8 @@ db.exec(`
     http_method TEXT NOT NULL DEFAULT 'GET',
     request_body TEXT,
     headers TEXT,
+    cache_mode TEXT NOT NULL DEFAULT 'normal',
+    gzip INTEGER NOT NULL DEFAULT 1,
     status TEXT NOT NULL DEFAULT 'pending',
     created_at INTEGER NOT NULL,
     finished_at INTEGER,
@@ -33,21 +35,43 @@ db.exec(`
   )
 `);
 
+// Non-destructive migration for existing DBs
+try { db.exec(`ALTER TABLE tests ADD COLUMN cache_mode TEXT NOT NULL DEFAULT 'normal'`); } catch {}
+try { db.exec(`ALTER TABLE tests ADD COLUMN gzip INTEGER NOT NULL DEFAULT 1`); } catch {}
+
 // Stream active test outputs (testId -> {process, clients})
 const activeTests = {};
 
 // Generate a k6 script from test params
 function generateScript(params) {
-  const { url, vus, duration, rpsLimit, httpMethod, requestBody, headers } = params;
+  const { url, vus, duration, rpsLimit, httpMethod, requestBody, headers, cacheMode, gzip } = params;
 
-  const parsedHeaders = (() => {
+  // Build the merged headers object
+  const userHeaders = (() => {
     try { return JSON.parse(headers || '{}'); } catch { return {}; }
   })();
 
-  const headersJs = Object.entries(parsedHeaders)
+  // Cache control headers
+  if (cacheMode === 'no-cache' || cacheMode === 'bust') {
+    userHeaders['Cache-Control'] = 'no-cache, no-store';
+    userHeaders['Pragma'] = 'no-cache';
+  }
+
+  // Encoding header
+  if (gzip === false || gzip === 0) {
+    userHeaders['Accept-Encoding'] = 'identity';
+  }
+  // When gzip=true, omit the header entirely so k6 sends its default (gzip, deflate, br)
+
+  const headersJs = Object.entries(userHeaders)
     .map(([k, v]) => `    '${k.replace(/'/g, "\\'")}': '${v.replace(/'/g, "\\'")}',`)
     .join('\n');
 
+  // For cache-bust mode, append a random query param per iteration
+  const targetUrl = cacheMode === 'bust'
+    ? `\`${url}${url.includes('?') ? '&' : '?'}_cb=\${Date.now()}-\${Math.random().toString(36).slice(2)}\``
+    : `'${url}'`;
+
   const bodyLine = (httpMethod !== 'GET' && httpMethod !== 'HEAD' && requestBody)
     ? `const body = \`${requestBody.replace(/`/g, '\\`')}\`;`
     : 'const body = null;';
@@ -84,7 +108,7 @@ ${headersJs}
     timeout: '30s',
   };
 
-  const res = http.${httpMethod.toLowerCase()}('${url}'${httpMethod !== 'GET' && httpMethod !== 'HEAD' ? ', body' : ''}, params);
+  const res = http.${httpMethod.toLowerCase()}(${targetUrl}${httpMethod !== 'GET' && httpMethod !== 'HEAD' ? ', body' : ''}, params);
 
   const ok = check(res, {
     'status is 2xx': (r) => r.status >= 200 && r.status < 300,
@@ -110,6 +134,8 @@ app.post('/api/tests', (req, res) => {
     httpMethod = 'GET',
     requestBody = '',
     headers = '{}',
+    cacheMode = 'normal',
+    gzip = true,
   } = req.body;
 
   if (!url || !url.startsWith('http')) {
@@ -120,11 +146,11 @@ app.post('/api/tests', (req, res) => {
   const createdAt = Date.now();
 
   db.prepare(`
-    INSERT INTO tests (id, url, vus, duration, rps_limit, http_method, request_body, headers, status, created_at)
-    VALUES (?, ?, ?, ?, ?, ?, ?, ?, 'running', ?)
-  `).run(id, url, vus, duration, rpsLimit || null, httpMethod, requestBody, headers, createdAt);
+    INSERT INTO tests (id, url, vus, duration, rps_limit, http_method, request_body, headers, cache_mode, gzip, status, created_at)
+    VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, 'running', ?)
+  `).run(id, url, vus, duration, rpsLimit || null, httpMethod, requestBody, headers, cacheMode, gzip ? 1 : 0, createdAt);
 
-  const script = generateScript({ url, vus, duration, rpsLimit, httpMethod, requestBody, headers });
+  const script = generateScript({ url, vus, duration, rpsLimit, httpMethod, requestBody, headers, cacheMode, gzip });
   const tmpScript = path.join(os.tmpdir(), `k6-script-${id}.js`);
   fs.writeFileSync(tmpScript, script);
 
@@ -208,7 +234,7 @@ app.get('/api/tests/:id/stream', (req, res) => {
 
 // GET /api/tests — list all tests
 app.get('/api/tests', (req, res) => {
-  const rows = db.prepare('SELECT id, url, vus, duration, rps_limit, http_method, status, created_at, finished_at, summary FROM tests ORDER BY created_at DESC LIMIT 50').all();
+  const rows = db.prepare('SELECT id, url, vus, duration, rps_limit, http_method, cache_mode, gzip, status, created_at, finished_at, summary FROM tests ORDER BY created_at DESC LIMIT 50').all();
   res.json(rows.map(r => ({ ...r, summary: r.summary ? JSON.parse(r.summary) : null })));
 });