diff --git a/src/background/commands.mjs b/src/background/commands.mjs
index 1440d74d..47577cf6 100644
--- a/src/background/commands.mjs
+++ b/src/background/commands.mjs
@@ -12,7 +12,25 @@ export function registerCommands() {
 
     if (command in menuConfig) {
       if (menuConfig[command].action) {
-        menuConfig[command].action(true, tab)
+        // The action may return a Promise (e.g. openSidePanel returns the
+        // chrome.sidePanel.open() Promise). Keep the call synchronous so the
+        // user-gesture context is preserved, but observe the Promise so a
+        // rejection does not become an unhandled rejection in the background.
+        // Also wrap in try/catch because Browser.commands.onCommand documents
+        // `tab` as optional, so an action that dereferences tab.* (e.g. the
+        // openSidePanel call) can throw synchronously.
+        let result
+        try {
+          result = menuConfig[command].action(true, tab)
+        } catch (error) {
+          console.error(`failed to run command action "${command}"`, error)
+          return
+        }
+        if (result && typeof result.catch === 'function') {
+          result.catch((error) => {
+            console.error(`failed to run command action "${command}"`, error)
+          })
+        }
       }
 
       if (menuConfig[command].genPrompt) {
diff --git a/src/background/menus.mjs b/src/background/menus.mjs
index a92bd7ba..7f086499 100644
--- a/src/background/menus.mjs
+++ b/src/background/menus.mjs
@@ -5,10 +5,39 @@ import { config as menuConfig } from '../content-script/menu-tools/index.mjs'
 
 const menuId = 'ChatGPTBox-Menu'
 const onClickMenu = (info, tab) => {
+  const itemId = info.menuItemId.replace(menuId, '')
+
+  // sidePanel.open() must be called synchronously within the user gesture handler.
+  // Calling it inside a Promise callback (e.g. Browser.tabs.query().then()) breaks
+  // Chrome's user gesture requirement and causes the error:
+  // "sidePanel.open() may only be called in response to a user gesture."
+  if (itemId === 'openSidePanel' && menuConfig.openSidePanel?.action) {
+    // Keep the call synchronous to preserve the user-gesture requirement,
+    // but observe the returned Promise so a rejected sidePanel.open() does
+    // not become an unhandled rejection in the background script.
+    // Also wrap in try/catch because contextMenus.onClicked documents `tab`
+    // as optional ("If the click did not take place in a tab, this parameter
+    // will be missing"), so the openSidePanel action that dereferences
+    // tab.windowId/tab.id can throw synchronously.
+    let result
+    try {
+      result = menuConfig.openSidePanel.action(true, tab)
+    } catch (error) {
+      console.error('failed to open side panel', error)
+      return
+    }
+    if (result && typeof result.catch === 'function') {
+      result.catch((error) => {
+        console.error('failed to open side panel', error)
+      })
+    }
+    return
+  }
+
   Browser.tabs.query({ active: true, currentWindow: true }).then((tabs) => {
     const currentTab = tabs[0]
     const message = {
-      itemId: info.menuItemId.replace(menuId, ''),
+      itemId,
       selectionText: info.selectionText,
       useMenuPosition: tab.id === currentTab.id,
     }
diff --git a/src/content-script/menu-tools/index.mjs b/src/content-script/menu-tools/index.mjs
index 0f46392e..21e82eea 100644
--- a/src/content-script/menu-tools/index.mjs
+++ b/src/content-script/menu-tools/index.mjs
@@ -59,14 +59,19 @@ export const config = {
   },
   openSidePanel: {
     label: 'Open Side Panel',
-    action: async (fromBackground, tab) => {
+    action: (fromBackground, tab) => {
       console.debug('action is from background', fromBackground)
       if (fromBackground) {
         // eslint-disable-next-line no-undef
-        chrome.sidePanel.open({ windowId: tab.windowId, tabId: tab.id })
-      } else {
-        // side panel is not supported
+        if (typeof chrome === 'undefined' || !chrome.sidePanel?.open) {
+          // sidePanel API is not available in this browser (e.g. Firefox)
+          return Promise.reject(new Error('chrome.sidePanel API is not available'))
+        }
+        // eslint-disable-next-line no-undef
+        return chrome.sidePanel.open({ windowId: tab.windowId, tabId: tab.id })
       }
+      // side panel is not supported
+      return undefined
     },
   },
   closeAllChats: {
diff --git a/src/services/clients/claude/index.mjs b/src/services/clients/claude/index.mjs
index c026f710..b20a487b 100644
--- a/src/services/clients/claude/index.mjs
+++ b/src/services/clients/claude/index.mjs
@@ -74,8 +74,8 @@ export class Claude {
     if (!sessionKey) {
       throw new Error('Session key required')
     }
-    if (!sessionKey.startsWith('sk-ant-sid01')) {
-      throw new Error('Session key invalid: Must be in the format sk-ant-sid01-*****')
+    if (!sessionKey.startsWith('sk-ant-sid')) {
+      throw new Error('Session key invalid: Must be in the format sk-ant-sid01-***** or sk-ant-sid02-*****')
     }
     if (fetch) {
       this.fetch = fetch