fix: address PR review - aria-pressed, O(N²) lookup, collapse bug

- Add aria-pressed to toggle buttons for accessibility
- Build nodeMap for O(1) lookups in clustering hook
- Always render dir node so expand/collapse works correctly

Author: DevanshuNEU

frontend/src/components/DependencyGraph/GraphToolbar.tsx

@@ -46,7 +46,8 @@ function GraphToolbarComponent({
           size="sm"
           onClick={onToggleCluster}
           className="h-8"
-          title="Group files by directory"
+          aria-pressed={clusterByDir}
+          title={clusterByDir ? 'Click to show flat view' : 'Group files by directory'}
         >
           <FolderTree className="w-3.5 h-3.5 mr-1.5" />
           Cluster
@@ -57,6 +58,8 @@ function GraphToolbarComponent({
           size="sm"
           onClick={onToggleShowAll}
           className="h-8"
+          aria-pressed={showAll}
+          title={showAll ? 'Show top 15 files' : 'Show all files'}
         >
           <Filter className="w-3.5 h-3.5 mr-1.5" />
           {showAll ? 'Show Top 15' : 'Show All'}
@@ -67,6 +70,7 @@ function GraphToolbarComponent({
           size="sm"
           onClick={onToggleTests}
           className={cn('h-8', !showTests && 'opacity-70 line-through')}
+          aria-pressed={showTests}
           title={showTests ? 'Click to hide test files' : 'Click to show test files'}
         >
           {showTests ? <Eye className="w-3.5 h-3.5 mr-1.5" /> : <EyeOff className="w-3.5 h-3.5 mr-1.5" />}

frontend/src/components/DependencyGraph/hooks/useDirectoryClustering.ts

@@ -48,6 +48,9 @@ export function useDirectoryClustering(
   const clusters = useMemo(() => {
     const clusterMap = new Map<string, DirectoryCluster>()
 
+    // Build node lookup map for O(1) access
+    const nodeMap = new Map(nodes.map(n => [n.id, n]))
+    
     // Group files by directory
     const dirFiles = new Map<string, string[]>()
     nodes.forEach(node => {
@@ -61,7 +64,7 @@ export function useDirectoryClustering(
     // Create clusters for each directory
     dirFiles.forEach((files, dirPath) => {
       const dirName = dirPath.split('/').pop() || dirPath
-      const nodeData = files.map(f => nodes.find(n => n.id === f)!).filter(Boolean)
+      const nodeData = files.map(f => nodeMap.get(f)!).filter(Boolean)
 
       clusterMap.set(dirPath, {
         path: dirPath,

frontend/src/components/DependencyGraph/index.tsx

@@ -179,26 +179,28 @@ function DependencyGraphInner({ repoId, apiUrl, apiKey }: DependencyGraphProps)
     dirFiles.forEach((files, dirPath) => {
       const isExpanded = expandedDirs.has(dirPath)
 
+      // Calculate metrics for this directory
+      const metrics = files.map(f => impact.getFileMetrics(f)).filter(Boolean)
+      const totalDeps = metrics.reduce((sum, m) => sum + (m?.dependentCount || 0), 0)
+      const risks = metrics.map(m => m?.riskLevel || 'low') as Array<'low' | 'medium' | 'high' | 'critical'>
+      
+      // Always create directory node so user can collapse
+      dirNodes.push({
+        id: `dir:${dirPath}`,
+        data: {
+          label: dirPath.split('/').pop() || dirPath,
+          fullPath: dirPath,
+          fileCount: files.length,
+          totalDependents: totalDeps,
+          maxRisk: getMaxRisk(risks),
+          isExpanded,
+          state: 'default',
+        }
+      })
+      
+      // When expanded, also show individual files
       if (isExpanded) {
         files.forEach(f => visibleFiles.add(f))
-      } else {
-        // Create directory node
-        const metrics = files.map(f => impact.getFileMetrics(f)).filter(Boolean)
-        const totalDeps = metrics.reduce((sum, m) => sum + (m?.dependentCount || 0), 0)
-        const risks = metrics.map(m => m?.riskLevel || 'low') as Array<'low' | 'medium' | 'high' | 'critical'>
-        
-        dirNodes.push({
-          id: `dir:${dirPath}`,
-          data: {
-            label: dirPath.split('/').pop() || dirPath,
-            fullPath: dirPath,
-            fileCount: files.length,
-            totalDependents: totalDeps,
-            maxRisk: getMaxRisk(risks),
-            isExpanded: false,
-            state: 'default',
-          }
-        })
       }
     })