♻️ refactor: extract Phase 1 hooks from sidebar (2187→2099 lines)

Extract 3 simple hooks with no UI dependencies:
- use-theme-preview.ts: Debounced theme preview on hover
- use-sidebar-auto-collapse.ts: Auto-collapse on small screens
- use-drag-and-drop.ts: Project reordering drag-and-drop

Benefits:
- Reduced sidebar.tsx by 88 lines (-4%)
- Improved testability (hooks can be tested in isolation)
- Removed unused imports (DragEndEvent, PointerSensor, useSensor, useSensors)
- Created hooks/ barrel export pattern

Next steps: Extract 10+ remaining hooks and 10+ UI sections to reach
target of 200-300 lines (current: 2099 lines, need to reduce ~1800 more)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

apps/ui/src/components/layout/sidebar.tsx

@@ -75,14 +75,7 @@ import { DeleteProjectDialog } from '@/components/views/settings-view/components
 import { NewProjectModal } from '@/components/dialogs/new-project-modal';
 import { CreateSpecDialog } from '@/components/views/spec-view/dialogs';
 import type { FeatureCount } from '@/components/views/spec-view/types';
-import {
-  DndContext,
-  DragEndEvent,
-  PointerSensor,
-  useSensor,
-  useSensors,
-  closestCenter,
-} from '@dnd-kit/core';
+import { DndContext, closestCenter } from '@dnd-kit/core';
 import { SortableContext, verticalListSortingStrategy } from '@dnd-kit/sortable';
 import { getHttpApiClient } from '@/lib/http-api-client';
 import type { StarterTemplate } from '@/lib/templates';
@@ -95,6 +88,7 @@ import {
   PROJECT_LIGHT_THEMES,
   SIDEBAR_FEATURE_FLAGS,
 } from './sidebar/constants';
+import { useThemePreview, useSidebarAutoCollapse, useDragAndDrop } from './sidebar/hooks';
 
 export function Sidebar() {
   const navigate = useNavigate();
@@ -164,45 +158,8 @@ export function Sidebar() {
   const [featureCount, setFeatureCount] = useState<FeatureCount>(50);
   const [showSpecIndicator, setShowSpecIndicator] = useState(true);
 
-  // Debounced preview theme handlers to prevent excessive re-renders
-  const previewTimeoutRef = useRef<ReturnType<typeof setTimeout> | null>(null);
-
-  const handlePreviewEnter = useCallback(
-    (value: string) => {
-      // Clear any pending timeout
-      if (previewTimeoutRef.current) {
-        clearTimeout(previewTimeoutRef.current);
-      }
-      // Small delay to debounce rapid hover changes
-      previewTimeoutRef.current = setTimeout(() => {
-        setPreviewTheme(value as ThemeMode);
-      }, 16); // ~1 frame delay
-    },
-    [setPreviewTheme]
-  );
-
-  const handlePreviewLeave = useCallback(
-    (e: React.PointerEvent) => {
-      const relatedTarget = e.relatedTarget as HTMLElement;
-      if (!relatedTarget?.closest('[data-testid^="project-theme-"]')) {
-        // Clear any pending timeout
-        if (previewTimeoutRef.current) {
-          clearTimeout(previewTimeoutRef.current);
-        }
-        setPreviewTheme(null);
-      }
-    },
-    [setPreviewTheme]
-  );
-
-  // Cleanup timeout on unmount
-  useEffect(() => {
-    return () => {
-      if (previewTimeoutRef.current) {
-        clearTimeout(previewTimeoutRef.current);
-      }
-    };
-  }, []);
+  // Debounced preview theme handlers
+  const { handlePreviewEnter, handlePreviewLeave } = useThemePreview({ setPreviewTheme });
 
   // Derive isCreatingSpec from store state
   const isCreatingSpec = specCreatingForProject !== null;
@@ -212,23 +169,7 @@ export function Sidebar() {
   const projectSearchInputRef = useRef<HTMLInputElement>(null);
 
   // Auto-collapse sidebar on small screens
-  useEffect(() => {
-    const mediaQuery = window.matchMedia('(max-width: 1024px)'); // lg breakpoint
-
-    const handleResize = () => {
-      if (mediaQuery.matches && sidebarOpen) {
-        // Auto-collapse on small screens
-        toggleSidebar();
-      }
-    };
-
-    // Check on mount
-    handleResize();
-
-    // Listen for changes
-    mediaQuery.addEventListener('change', handleResize);
-    return () => mediaQuery.removeEventListener('change', handleResize);
-  }, [sidebarOpen, toggleSidebar]);
+  useSidebarAutoCollapse({ sidebarOpen, toggleSidebar });
 
   // Filtered projects based on search query
   const filteredProjects = useMemo(() => {
@@ -262,31 +203,8 @@ export function Sidebar() {
     }
   }, [isProjectPickerOpen]);
 
-  // Sensors for drag-and-drop
-  const sensors = useSensors(
-    useSensor(PointerSensor, {
-      activationConstraint: {
-        distance: 5, // Small distance to start drag
-      },
-    })
-  );
-
-  // Handle drag end for reordering projects
-  const handleDragEnd = useCallback(
-    (event: DragEndEvent) => {
-      const { active, over } = event;
-
-      if (over && active.id !== over.id) {
-        const oldIndex = projects.findIndex((p) => p.id === active.id);
-        const newIndex = projects.findIndex((p) => p.id === over.id);
-
-        if (oldIndex !== -1 && newIndex !== -1) {
-          reorderProjects(oldIndex, newIndex);
-        }
-      }
-    },
-    [projects, reorderProjects]
-  );
+  // Drag-and-drop for project reordering
+  const { sensors, handleDragEnd } = useDragAndDrop({ projects, reorderProjects });
 
   // Subscribe to spec regeneration events
   useEffect(() => {

apps/ui/src/components/layout/sidebar/hooks/index.ts

@@ -0,0 +1,3 @@
+export { useThemePreview } from './use-theme-preview';
+export { useSidebarAutoCollapse } from './use-sidebar-auto-collapse';
+export { useDragAndDrop } from './use-drag-and-drop';

apps/ui/src/components/layout/sidebar/hooks/use-drag-and-drop.ts

@@ -0,0 +1,41 @@
+import { useCallback } from 'react';
+import { useSensors, useSensor, PointerSensor, type DragEndEvent } from '@dnd-kit/core';
+import type { Project } from '@/lib/electron';
+
+interface UseDragAndDropProps {
+  projects: Project[];
+  reorderProjects: (oldIndex: number, newIndex: number) => void;
+}
+
+export function useDragAndDrop({ projects, reorderProjects }: UseDragAndDropProps) {
+  // Sensors for drag-and-drop
+  const sensors = useSensors(
+    useSensor(PointerSensor, {
+      activationConstraint: {
+        distance: 5, // Small distance to start drag
+      },
+    })
+  );
+
+  // Handle drag end for reordering projects
+  const handleDragEnd = useCallback(
+    (event: DragEndEvent) => {
+      const { active, over } = event;
+
+      if (over && active.id !== over.id) {
+        const oldIndex = projects.findIndex((p) => p.id === active.id);
+        const newIndex = projects.findIndex((p) => p.id === over.id);
+
+        if (oldIndex !== -1 && newIndex !== -1) {
+          reorderProjects(oldIndex, newIndex);
+        }
+      }
+    },
+    [projects, reorderProjects]
+  );
+
+  return {
+    sensors,
+    handleDragEnd,
+  };
+}

apps/ui/src/components/layout/sidebar/hooks/use-sidebar-auto-collapse.ts

@@ -0,0 +1,30 @@
+import { useEffect } from 'react';
+
+interface UseSidebarAutoCollapseProps {
+  sidebarOpen: boolean;
+  toggleSidebar: () => void;
+}
+
+export function useSidebarAutoCollapse({
+  sidebarOpen,
+  toggleSidebar,
+}: UseSidebarAutoCollapseProps) {
+  // Auto-collapse sidebar on small screens
+  useEffect(() => {
+    const mediaQuery = window.matchMedia('(max-width: 1024px)'); // lg breakpoint
+
+    const handleResize = () => {
+      if (mediaQuery.matches && sidebarOpen) {
+        // Auto-collapse on small screens
+        toggleSidebar();
+      }
+    };
+
+    // Check on mount
+    handleResize();
+
+    // Listen for changes
+    mediaQuery.addEventListener('change', handleResize);
+    return () => mediaQuery.removeEventListener('change', handleResize);
+  }, [sidebarOpen, toggleSidebar]);
+}

apps/ui/src/components/layout/sidebar/hooks/use-theme-preview.ts

@@ -0,0 +1,53 @@
+import { useRef, useCallback, useEffect } from 'react';
+import type { ThemeMode } from '@/store/app-store';
+
+interface UseThemePreviewProps {
+  setPreviewTheme: (theme: ThemeMode | null) => void;
+}
+
+export function useThemePreview({ setPreviewTheme }: UseThemePreviewProps) {
+  // Debounced preview theme handlers to prevent excessive re-renders
+  const previewTimeoutRef = useRef<ReturnType<typeof setTimeout> | null>(null);
+
+  const handlePreviewEnter = useCallback(
+    (value: string) => {
+      // Clear any pending timeout
+      if (previewTimeoutRef.current) {
+        clearTimeout(previewTimeoutRef.current);
+      }
+      // Small delay to debounce rapid hover changes
+      previewTimeoutRef.current = setTimeout(() => {
+        setPreviewTheme(value as ThemeMode);
+      }, 16); // ~1 frame delay
+    },
+    [setPreviewTheme]
+  );
+
+  const handlePreviewLeave = useCallback(
+    (e: React.PointerEvent) => {
+      const relatedTarget = e.relatedTarget as HTMLElement;
+      if (!relatedTarget?.closest('[data-testid^="project-theme-"]')) {
+        // Clear any pending timeout
+        if (previewTimeoutRef.current) {
+          clearTimeout(previewTimeoutRef.current);
+        }
+        setPreviewTheme(null);
+      }
+    },
+    [setPreviewTheme]
+  );
+
+  // Cleanup timeout on unmount
+  useEffect(() => {
+    return () => {
+      if (previewTimeoutRef.current) {
+        clearTimeout(previewTimeoutRef.current);
+      }
+    };
+  }, []);
+
+  return {
+    handlePreviewEnter,
+    handlePreviewLeave,
+  };
+}