fix: stop background diff and explorer work

frontend/src/components/SessionView.tsx

@@ -973,7 +973,7 @@ export const SessionView = memo(() => {
                       .filter(p => !defaultTerminalPanel || p.id !== defaultTerminalPanel.id)
                       .map(panel => {
                         const isActive = panel.id === currentActivePanel.id;
-                        const shouldKeepAlive = ['terminal', 'browser', 'diff', 'explorer'].includes(panel.type);
+                        const shouldKeepAlive = ['terminal', 'browser'].includes(panel.type);
                         if (!isActive && !shouldKeepAlive) return null;
                         return (
                           <div
@@ -1116,7 +1116,7 @@ export const SessionView = memo(() => {
                       .filter(p => !defaultTerminalPanel || p.id !== defaultTerminalPanel.id)
                       .map(panel => {
                         const isActive = panel.id === currentActivePanel.id;
-                        const shouldKeepAlive = ['terminal', 'browser', 'diff', 'explorer'].includes(panel.type);
+                        const shouldKeepAlive = ['terminal', 'browser'].includes(panel.type);
                         if (!isActive && !shouldKeepAlive) return null;
                         return (
                           <div

frontend/src/components/panels/diff/CombinedDiffView.tsx

@@ -99,8 +99,6 @@ const CombinedDiffView = memo(forwardRef<CombinedDiffViewHandle, CombinedDiffVie
   const [isResizing, setIsResizing] = useState(false);
 
   const diffViewerRef = useRef<DiffViewerHandle>(null);
-  // Track diff-relevant git state to avoid spurious prefetches on no-op status events
-  const lastGitFingerprintRef = useRef<string>('');
 
   // Expose refresh() to parent (DiffPanel) via ref
   // Keeps current diff visible while new data loads (no flash),
@@ -186,7 +184,6 @@ const CombinedDiffView = memo(forwardRef<CombinedDiffViewHandle, CombinedDiffVie
       setExecutions([]);
       setHistorySource(isMainRepo ? 'remote' : 'branch');
       diffCacheRef.current.clear();
-      lastGitFingerprintRef.current = '';
     }
   }, [sessionId, lastSessionId, isMainRepo]);
 
@@ -314,46 +311,9 @@ const CombinedDiffView = memo(forwardRef<CombinedDiffViewHandle, CombinedDiffVie
   // eslint-disable-next-line react-hooks/exhaustive-deps -- selectedExecutions read inside closure to check if auto-select needed; must not re-trigger on selection change
   }, [sessionId, isMainRepo, forceRefresh, isVisible, processExecutions]);
 
-  // Background prefetch: when git status changes, fetch executions + diff even when not visible
-  // This ensures the diff tab has data ready before the user opens it
-  useEffect(() => {
-    if (!isVisible) return;
-    let cancelled = false;
-
-    const handleGitStatusUpdated = (event: Event) => {
-      const { sessionId: eventSessionId, gitStatus } = (event as CustomEvent).detail || {};
-      if (eventSessionId !== sessionId) return;
-
-      // Fingerprint diff-relevant fields — ignore no-op status refreshes
-      const fingerprint = `${gitStatus?.state}-${gitStatus?.ahead}-${gitStatus?.behind}-${gitStatus?.uncommittedChanges}`;
-      if (fingerprint === lastGitFingerprintRef.current) return;
-      lastGitFingerprintRef.current = fingerprint;
-
-      // Clear stale cache and force diff re-fetch for existing selection
-      diffCacheRef.current.clear();
-      setForceRefresh(prev => prev + 1);
-
-      // Prefetch executions and let the diff loading effect chain handle the rest
-      // Only auto-select if user hasn't made a custom selection (preserves their commit range)
-      API.sessions.getExecutions(sessionId).then(response => {
-        if (cancelled || !response.success) return;
-        const data: ExecutionDiff[] = response.data || [];
-        processExecutions(data, selectedExecutionsRef.current.length === 0);
-      }).catch(() => { /* silent — prefetch is best-effort */ });
-    };
-
-    window.addEventListener('git-status-updated', handleGitStatusUpdated);
-    return () => {
-      cancelled = true;
-      window.removeEventListener('git-status-updated', handleGitStatusUpdated);
-    };
-  }, [sessionId, isVisible, processExecutions]);
-
   // Keep refs to avoid stale closures in event handlers
   const executionsLengthRef = useRef(executions.length);
   executionsLengthRef.current = executions.length;
-  const selectedExecutionsRef = useRef(selectedExecutions);
-  selectedExecutionsRef.current = selectedExecutions;
   const viewingCommitHashRef = useRef(viewingCommitHash);
   viewingCommitHashRef.current = viewingCommitHash;
 
@@ -428,7 +388,6 @@ const CombinedDiffView = memo(forwardRef<CombinedDiffViewHandle, CombinedDiffVie
       cancelled = true;
       clearTimeout(timeoutId);
     };
-    // eslint-disable-next-line react-hooks/exhaustive-deps -- executions.length read via ref to avoid re-triggering when executions reload
   }, [selectedExecutions, sessionId, forceRefresh]);
 
   const handleSelectionChange = (newSelection: number[]) => {

frontend/src/components/panels/diff/DiffPanel.tsx

@@ -3,9 +3,6 @@ import CombinedDiffView from './CombinedDiffView';
 import type { CombinedDiffViewHandle } from './CombinedDiffView';
 import type { ToolPanel, DiffPanelState } from '../../../../../shared/types/panels';
 import { AlertCircle } from 'lucide-react';
-import { useSession } from '../../../contexts/SessionContext';
-
-const DIFF_PRELOAD_DELAY_MS = 10000;
 
 interface DiffPanelProps {
   panel: ToolPanel;
@@ -20,32 +17,12 @@ export const DiffPanel: React.FC<DiffPanelProps> = ({
   sessionId,
   isMainRepo = false
 }) => {
-  const sessionContext = useSession();
   const [isStale, setIsStale] = useState(false);
-  const [backgroundPreloadReady, setBackgroundPreloadReady] = useState(isActive);
   const diffState = panel.state?.customState as DiffPanelState | undefined;
   const lastRefreshRef = useRef<number>(Date.now());
   const combinedDiffRef = useRef<CombinedDiffViewHandle>(null);
   // Track diff-relevant git state to avoid spurious refreshes on no-op status events
   const lastGitFingerprintRef = useRef<string>('');
-  const sessionStatus = sessionContext?.session.status;
-  const isSessionBusy = sessionStatus === 'running' || sessionStatus === 'initializing';
-  const shouldLoadDiff = isActive || (backgroundPreloadReady && !isSessionBusy);
-
-  useEffect(() => {
-    if (isActive) {
-      setBackgroundPreloadReady(true);
-      return;
-    }
-
-    if (backgroundPreloadReady || isSessionBusy) return;
-
-    const timer = window.setTimeout(() => {
-      setBackgroundPreloadReady(true);
-    }, DIFF_PRELOAD_DELAY_MS);
-
-    return () => window.clearTimeout(timer);
-  }, [isActive, backgroundPreloadReady, isSessionBusy]);
 
   // Listen for file change events from other panels
   useEffect(() => {
@@ -152,7 +129,7 @@ export const DiffPanel: React.FC<DiffPanelProps> = ({
           selectedExecutions={[]}
           isGitOperationRunning={false}
           isMainRepo={isMainRepo}
-          isVisible={shouldLoadDiff}
+          isVisible={isActive}
         />
       </div>
     </div>

frontend/src/components/panels/editor/EditorPanel.tsx

@@ -150,6 +150,20 @@ export const ExplorerPanel: React.FC<ExplorerPanelProps> = ({
       handleStateChange({ filePath, isDirty });
     }
   }, [panel.id, handleStateChange]);
+
+  // Only render when active. Explorer is cheap to initialize and should not
+  // keep Monaco, file tree loading, or git file-status checks alive in the
+  // background while the user is working in another panel.
+  if (!isActive) {
+    return (
+      <div className="flex-1 flex items-center justify-center text-text-secondary">
+        <div className="text-center">
+          <div className="text-sm">Explorer panel not active</div>
+          <div className="text-xs mt-1 text-text-tertiary">Click to activate</div>
+        </div>
+      </div>
+    );
+  }
 
   return (
     <div className="h-full w-full">