diff --git a/src/web-ui/src/flow_chat/components/ChatInput.tsx b/src/web-ui/src/flow_chat/components/ChatInput.tsx
index 300886164..2703b242f 100644
--- a/src/web-ui/src/flow_chat/components/ChatInput.tsx
+++ b/src/web-ui/src/flow_chat/components/ChatInput.tsx
@@ -68,6 +68,28 @@ import { deriveDeepReviewSessionConcurrencyGuard } from '../utils/deepReviewCapa
 import { agentAPI } from '@/infrastructure/api/service-api/AgentAPI';
 import './ChatInput.scss';
 
+// Module-level popup state – used by ModernFlowChatContainer to conditionally
+// disable the Escape shortcut so that slash-command and @-mention popups can be
+// closed with Escape.
+let _chatPopupActive = false;
+const _chatPopupListeners = new Set<() => void>();
+
+export function isChatPopupActive(): boolean {
+  return _chatPopupActive;
+}
+
+export function subscribeChatPopupChange(listener: () => void): () => void {
+  _chatPopupListeners.add(listener);
+  return () => { _chatPopupListeners.delete(listener); };
+}
+
+function setChatPopupActive(active: boolean) {
+  if (_chatPopupActive !== active) {
+    _chatPopupActive = active;
+    _chatPopupListeners.forEach(fn => fn());
+  }
+}
+
 const log = createLogger('ChatInput');
 
 export interface ChatInputProps {
@@ -819,6 +841,12 @@ export const ChatInput: React.FC<ChatInputProps> = ({
     selectedIndex: 0,
   });
 
+  // Keep the module-level popup-active flag in sync so ModernFlowChatContainer
+  // can disable the global Escape shortcut while popups are open.
+  useEffect(() => {
+    setChatPopupActive(slashCommandState.isActive || mentionState.isActive);
+  }, [slashCommandState.isActive, mentionState.isActive]);
+
   const clearPendingLargePastes = useCallback(() => {
     pendingLargePastesRef.current = {};
   }, []);
diff --git a/src/web-ui/src/flow_chat/components/modern/ModernFlowChatContainer.tsx b/src/web-ui/src/flow_chat/components/modern/ModernFlowChatContainer.tsx
index 5dea6aec6..3b3b0d4b3 100644
--- a/src/web-ui/src/flow_chat/components/modern/ModernFlowChatContainer.tsx
+++ b/src/web-ui/src/flow_chat/components/modern/ModernFlowChatContainer.tsx
@@ -23,6 +23,7 @@ import { useFlowChatSearch } from './useFlowChatSearch';
 import { useVirtualItems, useActiveSession, useVisibleTurnInfo, type VisibleTurnInfo } from '../../store/modernFlowChatStore';
 import type { FlowChatConfig, FlowToolItem, Session, DialogTurn } from '../../types/flow-chat';
 import type { LineRange } from '@/component-library';
+import { isChatPopupActive, subscribeChatPopupChange } from '../ChatInput';
 import { useWorkspaceContext } from '@/infrastructure/contexts/WorkspaceContext';
 import { parsePullRequestUrl } from '@/shared/utils/pullRequestLinks';
 import { createReviewPlatformPullRequestDetailTab } from '@/shared/utils/tabUtils';
@@ -171,6 +172,16 @@ export const ModernFlowChatContainer: React.FC<ModernFlowChatContainerProps> = (
   const visibleTurnInfo = useVisibleTurnInfo();
   const [pendingHeaderTurnId, setPendingHeaderTurnId] = useState<string | null>(null);
   const [searchOpenRequest, setSearchOpenRequest] = useState(0);
+  // Track whether a slash-command or @-mention popup is open in ChatInput.
+  // When a popup is active, the global Escape shortcut is disabled so the
+  // popup can be closed with Escape instead of cancelling the current task.
+  const [chatPopupActive, setChatPopupActive] = useState(() => isChatPopupActive());
+
+  useEffect(() => {
+    return subscribeChatPopupChange(() => {
+      setChatPopupActive(isChatPopupActive());
+    });
+  }, []);
   const [backgroundSubagents, setBackgroundSubagents] = useState<BackgroundSubagentSummary[]>([]);
   const autoPinnedSessionIdRef = useRef<string | null>(null);
   const virtualListRef = useRef<VirtualMessageListRef>(null);
@@ -474,7 +485,7 @@ export const ModernFlowChatContainer: React.FC<ModernFlowChatContainerProps> = (
     () => {
       void FlowChatManager.getInstance().cancelCurrentTask();
     },
-    { priority: 20, description: 'keyboard.shortcuts.chat.stopGeneration' }
+    { priority: 20, enabled: !chatPopupActive, description: 'keyboard.shortcuts.chat.stopGeneration' }
   );
 
   useShortcut(
diff --git a/src/web-ui/src/tools/mermaid-editor/theme/mermaidTheme.ts b/src/web-ui/src/tools/mermaid-editor/theme/mermaidTheme.ts
index 7bd12c5df..7f51360ca 100644
--- a/src/web-ui/src/tools/mermaid-editor/theme/mermaidTheme.ts
+++ b/src/web-ui/src/tools/mermaid-editor/theme/mermaidTheme.ts
@@ -26,6 +26,7 @@ export function getThemeType(): 'dark' | 'light' {
   if (dataTheme?.includes('light')) return 'light';
   if (dataTheme?.includes('dark')) return 'dark';
   if (document.documentElement.classList.contains('light')) return 'light';
+  if (typeof window.matchMedia !== 'function') return 'dark';
   return window.matchMedia('(prefers-color-scheme: dark)').matches ? 'dark' : 'light';
 }