fix: sidebar arrow hint stays visible until sidebar actually opens

Previously the welcome page arrow hid immediately when the extension's
content script loaded — but extension loaded ≠ sidebar open. Now the
signal flow is: sidepanel connects → tells background.js → relays to
content script → dispatches gstack-extension-ready → arrow hides.

Adds welcome-page.test.ts: 14 tests verifying arrow, branding, feature
cards, dark theme, and auto-hide behavior via real HTTP server.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

extension/background.js

@@ -286,7 +286,7 @@ chrome.runtime.onMessage.addListener((msg, sender, sendResponse) => {
 
   const ALLOWED_TYPES = new Set([
     'getPort', 'setPort', 'getServerUrl', 'fetchRefs',
-    'openSidePanel', 'command', 'sidebar-command',
+    'openSidePanel', 'sidebarOpened', 'command', 'sidebar-command',
     // Inspector message types
     'startInspector', 'stopInspector', 'elementPicked', 'pickerCancelled',
     'applyStyle', 'toggleClass', 'injectCSS', 'resetAll',
@@ -332,6 +332,20 @@ chrome.runtime.onMessage.addListener((msg, sender, sendResponse) => {
     return;
   }
 
+  // Sidebar opened — tell active tab's content script so the welcome page
+  // can hide its arrow hint. Only fires when the sidebar actually connects.
+  if (msg.type === 'sidebarOpened') {
+    chrome.tabs.query({ active: true, currentWindow: true }, (tabs) => {
+      const tabId = tabs?.[0]?.id;
+      if (tabId) {
+        chrome.tabs.sendMessage(tabId, { type: 'sidebarOpened' }).catch(() => {
+          // Expected: tab may not have content script
+        });
+      }
+    });
+    return;
+  }
+
   // Inspector: inject + start picker
   if (msg.type === 'startInspector') {
     chrome.tabs.query({ active: true, currentWindow: true }, (tabs) => {

extension/content.js

@@ -326,11 +326,18 @@ function startBasicPicker() {
   document.addEventListener('keydown', onBasicKeydown, true);
 }
 
-// Notify the page that the gstack extension is active (used by welcome page)
-document.dispatchEvent(new CustomEvent('gstack-extension-ready'));
+// Do NOT dispatch gstack-extension-ready here — the extension being loaded
+// does not mean the sidebar is open. The welcome page arrow hint should only
+// hide when the sidebar is actually open. We dispatch it when we receive
+// a 'sidebarOpened' message from background.js.
 
 // Listen for messages from background worker
 chrome.runtime.onMessage.addListener((msg) => {
+  // Sidebar actually opened — now hide the welcome page arrow hint
+  if (msg.type === 'sidebarOpened') {
+    document.dispatchEvent(new CustomEvent('gstack-extension-ready'));
+    return;
+  }
   if (msg.type === 'startBasicPicker') {
     startBasicPicker();
     return;

extension/sidepanel.js

@@ -1352,6 +1352,9 @@ function updateConnection(url, token) {
     document.getElementById('footer-port').textContent = `:${port}`;
     setConnState('connected');
     setActionButtonsEnabled(true);
+    // Tell the active tab's content script the sidebar is open — this hides
+    // the welcome page arrow hint. Only fires on actual sidebar connection.
+    chrome.runtime.sendMessage({ type: 'sidebarOpened' }).catch(() => {});
     connectSSE();
     connectInspectorSSE();
     if (chatPollInterval) clearInterval(chatPollInterval);