fix(chart): transaction mapping fix + add cache for suggestions

- Fix transaction.mapping.map usage - it returns a position, not mapping
- Add 5-minute in-memory cache for chart suggestions (max 50 entries)
- Cache key based on content hash + selection
- Significantly improves UX when re-analyzing same content

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

memento-note/components/rich-text-editor.tsx

@@ -297,7 +297,7 @@ export const RichTextEditor = forwardRef<RichTextEditorHandle, RichTextEditorPro
       try {
         console.log('[handleSelectChart] Inserting chart type:', chartContent.split('\n')[0])
 
-        const { from, to } = editor.state.selection
+        const { from } = editor.state.selection
         const { tr } = editor.state
         const { schema } = editor.state
 
@@ -313,17 +313,21 @@ export const RichTextEditor = forwardRef<RichTextEditorHandle, RichTextEditorPro
           return
         }
 
-        // Replace selection with the chart node
-        const transaction = tr.replaceWith(from, to, chartNode)
+        // Insert the chart node at current position
+        const transaction = tr.insert(from, chartNode)
+
+        // Get the position after the inserted chart
+        const insertPos = transaction.mapping.map(from)
+        const chartSize = chartNode.nodeSize
 
         // Add a paragraph after for continued typing
         const paragraph = schema.nodes.paragraph.create()
-        transaction.insert(transaction.mapping.map(to).map(to), paragraph)
+        transaction.insert(insertPos + chartSize, paragraph)
 
         editor.view.dispatch(transaction)
         editor.chain().focus().run()
 
-        console.log('[handleSelectChart] Chart inserted')
+        console.log('[handleSelectChart] Chart inserted successfully')
       } catch (error) {
         console.error('[handleSelectChart] Failed:', error)
         toast.error('Failed to insert chart: ' + (error as Error).message)

memento-note/lib/ai/services/chart-suggestion.service.ts

@@ -26,12 +26,55 @@ export interface SuggestChartsRequest {
   noteId?: string
 }
 
+// Simple in-memory cache with 5-minute TTL
+const CACHE_TTL = 5 * 60 * 1000 // 5 minutes
+const cache = new Map<string, { data: SuggestChartsResponse; timestamp: number }>()
+
+function getCacheKey(content: string, selection: string | null | undefined): string {
+  // Use content hash + selection as cache key
+  const textToHash = selection ? content + ':::' + selection : content
+  // Simple hash function
+  let hash = 0
+  for (let i = 0; i < textToHash.length; i++) {
+    hash = ((hash << 5) - hash) + textToHash.charCodeAt(i)
+    hash = hash & hash // Convert to 32bit integer
+  }
+  return String(hash)
+}
+
+function getCached(key: string): SuggestChartsResponse | null {
+  const entry = cache.get(key)
+  if (!entry) return null
+  if (Date.now() - entry.timestamp > CACHE_TTL) {
+    cache.delete(key)
+    return null
+  }
+  console.log('[chart-suggestion] Cache hit for key:', key)
+  return entry.data
+}
+
+function setCached(key: string, data: SuggestChartsResponse): void {
+  cache.set(key, { data, timestamp: Date.now() })
+  // Limit cache size to 50 entries
+  if (cache.size > 50) {
+    const firstKey = cache.keys().next().value
+    cache.delete(firstKey)
+  }
+}
+
 /**
  * Call the AI chart suggestions API
  * @param request - The request parameters
  * @returns Promise with the chart suggestions
  */
 export async function suggestCharts(request: SuggestChartsRequest): Promise<SuggestChartsResponse> {
+  // Check cache first
+  const cacheKey = getCacheKey(request.content || '', request.selection)
+  const cached = getCached(cacheKey)
+  if (cached) {
+    return cached
+  }
+
   try {
     const response = await fetch('/api/ai/suggest-charts', {
       method: 'POST',
@@ -56,8 +99,14 @@ export async function suggestCharts(request: SuggestChartsRequest): Promise<Sugg
       }
     }
 
-    const data = await response.json()
-    return data as SuggestChartsResponse
+    const data = await response.json() as SuggestChartsResponse
+
+    // Cache successful responses
+    if (!data.error && !data.quotaExceeded) {
+      setCached(cacheKey, data)
+    }
+
+    return data
   } catch (error) {
     console.error('[suggestCharts] Network error:', error)
     return {