feat(ui): add infinite scroll for notebook sources

Previously, notebook sources were limited to 50 items due to API default.
This adds pagination with infinite scroll to the sources column:

- Add useNotebookSources hook with useInfiniteQuery for paginated fetching
- Update SourcesColumn with scroll detection to load more sources
- Fetch 30 sources per page, loading more as user scrolls near bottom

frontend/src/app/(dashboard)/notebooks/[id]/page.tsx

@@ -8,7 +8,7 @@ import { SourcesColumn } from '../components/SourcesColumn'
 import { NotesColumn } from '../components/NotesColumn'
 import { ChatColumn } from '../components/ChatColumn'
 import { useNotebook } from '@/lib/hooks/use-notebooks'
-import { useSources } from '@/lib/hooks/use-sources'
+import { useNotebookSources } from '@/lib/hooks/use-sources'
 import { useNotes } from '@/lib/hooks/use-notes'
 import { LoadingSpinner } from '@/components/common/LoadingSpinner'
 import { useNotebookColumnsStore } from '@/lib/stores/notebook-columns-store'
@@ -31,7 +31,14 @@ export default function NotebookPage() {
   const notebookId = decodeURIComponent(params.id as string)
 
   const { data: notebook, isLoading: notebookLoading } = useNotebook(notebookId)
-  const { data: sources, isLoading: sourcesLoading, refetch: refetchSources } = useSources(notebookId)
+  const {
+    sources,
+    isLoading: sourcesLoading,
+    refetch: refetchSources,
+    hasNextPage,
+    isFetchingNextPage,
+    fetchNextPage,
+  } = useNotebookSources(notebookId)
   const { data: notes, isLoading: notesLoading } = useNotes(notebookId)
 
   // Get collapse states for dynamic layout
@@ -153,6 +160,9 @@ export default function NotebookPage() {
                     onRefresh={refetchSources}
                     contextSelections={contextSelections.sources}
                     onContextModeChange={(sourceId, mode) => handleContextModeChange(sourceId, mode, 'source')}
+                    hasNextPage={hasNextPage}
+                    isFetchingNextPage={isFetchingNextPage}
+                    fetchNextPage={fetchNextPage}
                   />
                 )}
                 {mobileActiveTab === 'notes' && (
@@ -192,6 +202,9 @@ export default function NotebookPage() {
                 onRefresh={refetchSources}
                 contextSelections={contextSelections.sources}
                 onContextModeChange={(sourceId, mode) => handleContextModeChange(sourceId, mode, 'source')}
+                hasNextPage={hasNextPage}
+                isFetchingNextPage={isFetchingNextPage}
+                fetchNextPage={fetchNextPage}
               />
             </div>
 

frontend/src/app/(dashboard)/notebooks/components/SourcesColumn.tsx

@@ -1,6 +1,6 @@
 'use client'
 
-import { useState, useMemo } from 'react'
+import { useState, useMemo, useRef, useCallback, useEffect } from 'react'
 import { SourceListResponse } from '@/lib/types/api'
 import { Button } from '@/components/ui/button'
 import { Card, CardContent, CardHeader, CardTitle } from '@/components/ui/card'
@@ -10,7 +10,7 @@ import {
   DropdownMenuItem,
   DropdownMenuTrigger,
 } from '@/components/ui/dropdown-menu'
-import { Plus, FileText, Link2, ChevronDown } from 'lucide-react'
+import { Plus, FileText, Link2, ChevronDown, Loader2 } from 'lucide-react'
 import { LoadingSpinner } from '@/components/common/LoadingSpinner'
 import { EmptyState } from '@/components/common/EmptyState'
 import { AddSourceDialog } from '@/components/sources/AddSourceDialog'
@@ -31,6 +31,10 @@ interface SourcesColumnProps {
   onRefresh?: () => void
   contextSelections?: Record<string, ContextMode>
   onContextModeChange?: (sourceId: string, mode: ContextMode) => void
+  // Pagination props
+  hasNextPage?: boolean
+  isFetchingNextPage?: boolean
+  fetchNextPage?: () => void
 }
 
 export function SourcesColumn({
@@ -39,7 +43,10 @@ export function SourcesColumn({
   notebookId,
   onRefresh,
   contextSelections,
-  onContextModeChange
+  onContextModeChange,
+  hasNextPage,
+  isFetchingNextPage,
+  fetchNextPage,
 }: SourcesColumnProps) {
   const [dropdownOpen, setDropdownOpen] = useState(false)
   const [addDialogOpen, setAddDialogOpen] = useState(false)
@@ -60,6 +67,30 @@ export function SourcesColumn({
     () => createCollapseButton(toggleSources, 'Sources'),
     [toggleSources]
   )
+
+  // Scroll container ref for infinite scroll
+  const scrollContainerRef = useRef<HTMLDivElement>(null)
+
+  // Handle scroll for infinite loading
+  const handleScroll = useCallback(() => {
+    const container = scrollContainerRef.current
+    if (!container || !hasNextPage || isFetchingNextPage || !fetchNextPage) return
+
+    const { scrollTop, scrollHeight, clientHeight } = container
+    // Load more when user scrolls within 200px of the bottom
+    if (scrollHeight - scrollTop - clientHeight < 200) {
+      fetchNextPage()
+    }
+  }, [hasNextPage, isFetchingNextPage, fetchNextPage])
+
+  // Attach scroll listener
+  useEffect(() => {
+    const container = scrollContainerRef.current
+    if (!container) return
+
+    container.addEventListener('scroll', handleScroll)
+    return () => container.removeEventListener('scroll', handleScroll)
+  }, [handleScroll])
   
   const handleDeleteClick = (sourceId: string) => {
     setSourceToDelete(sourceId)
@@ -149,7 +180,7 @@ export function SourcesColumn({
             </div>
           </CardHeader>
 
-          <CardContent className="flex-1 overflow-y-auto min-h-0">
+          <CardContent ref={scrollContainerRef} className="flex-1 overflow-y-auto min-h-0">
             {isLoading ? (
               <div className="flex items-center justify-center py-8">
                 <LoadingSpinner />
@@ -179,6 +210,12 @@ export function SourcesColumn({
                     }
                   />
                 ))}
+                {/* Loading indicator for infinite scroll */}
+                {isFetchingNextPage && (
+                  <div className="flex items-center justify-center py-4">
+                    <Loader2 className="h-5 w-5 animate-spin text-muted-foreground" />
+                  </div>
+                )}
               </div>
             )}
           </CardContent>

frontend/src/lib/hooks/use-sources.ts

@@ -1,14 +1,18 @@
-import { useQuery, useMutation, useQueryClient } from '@tanstack/react-query'
+import { useQuery, useMutation, useQueryClient, useInfiniteQuery } from '@tanstack/react-query'
+import { useCallback } from 'react'
 import { sourcesApi } from '@/lib/api/sources'
 import { QUERY_KEYS } from '@/lib/api/query-client'
 import { useToast } from '@/lib/hooks/use-toast'
-import { 
-  CreateSourceRequest, 
-  UpdateSourceRequest, 
+import {
+  CreateSourceRequest,
+  UpdateSourceRequest,
   SourceResponse,
-  SourceStatusResponse 
+  SourceStatusResponse,
+  SourceListResponse
 } from '@/lib/types/api'
 
+const NOTEBOOK_SOURCES_PAGE_SIZE = 30
+
 export function useSources(notebookId?: string) {
   return useQuery({
     queryKey: QUERY_KEYS.sources(notebookId),
@@ -19,6 +23,54 @@ export function useSources(notebookId?: string) {
   })
 }
 
+/**
+ * Hook for fetching notebook sources with infinite scroll pagination.
+ * Returns flattened sources array and pagination controls.
+ */
+export function useNotebookSources(notebookId: string) {
+  const queryClient = useQueryClient()
+
+  const query = useInfiniteQuery({
+    queryKey: ['notebookSources', notebookId],
+    queryFn: async ({ pageParam = 0 }) => {
+      const data = await sourcesApi.list({
+        notebook_id: notebookId,
+        limit: NOTEBOOK_SOURCES_PAGE_SIZE,
+        offset: pageParam,
+        sort_by: 'updated',
+        sort_order: 'desc',
+      })
+      return {
+        sources: data,
+        nextOffset: data.length === NOTEBOOK_SOURCES_PAGE_SIZE ? pageParam + data.length : undefined,
+      }
+    },
+    initialPageParam: 0,
+    getNextPageParam: (lastPage) => lastPage.nextOffset,
+    enabled: !!notebookId,
+    staleTime: 5 * 1000,
+    refetchOnWindowFocus: true,
+  })
+
+  // Flatten all pages into a single array
+  const sources: SourceListResponse[] = query.data?.pages.flatMap(page => page.sources) ?? []
+
+  // Refetch function that resets to first page
+  const refetch = useCallback(() => {
+    queryClient.invalidateQueries({ queryKey: ['notebookSources', notebookId] })
+  }, [queryClient, notebookId])
+
+  return {
+    sources,
+    isLoading: query.isLoading,
+    isFetchingNextPage: query.isFetchingNextPage,
+    hasNextPage: query.hasNextPage,
+    fetchNextPage: query.fetchNextPage,
+    refetch,
+    error: query.error,
+  }
+}
+
 export function useSource(id: string) {
   return useQuery({
     queryKey: QUERY_KEYS.source(id),