fix: restore diagram when chartXML changes after iframe ready

The previous logic only restored on iframe ready, but chartXML might
be set AFTER the iframe is ready (session loaded after iframe).

Now we track the last restored XML and load whenever chartXML changes
to a new real diagram while iframe is ready.

app/[lang]/page.tsx

@@ -33,6 +33,7 @@ export default function Home() {
     const [isDrawioReady, setIsDrawioReady] = useState(false)
     const [isElectron, setIsElectron] = useState(false)
     const [canPersist, setCanPersist] = useState(false)
+    const [canPersistChecked, setCanPersistChecked] = useState(false)
     const [drawioBaseUrl, setDrawioBaseUrl] = useState(
         process.env.NEXT_PUBLIC_DRAWIO_BASE_URL || "https://embed.diagrams.net",
     )
@@ -86,6 +87,7 @@ export default function Home() {
         void (async () => {
             const usable = await isIndexedDBUsable()
             setCanPersist(usable)
+            setCanPersistChecked(true)
         })()
         setIsLoaded(true)
     }, [pathname, router])
@@ -189,7 +191,7 @@ export default function Home() {
                         }`}
                     >
                         <div className="h-full rounded-xl overflow-hidden shadow-soft-lg border border-border/30 relative">
-                            {isLoaded && (
+                            {isLoaded && canPersistChecked && (
                                 <div
                                     className={`h-full w-full ${isDrawioReady ? "" : "invisible absolute inset-0"}`}
                                 >

contexts/diagram-context.tsx

@@ -57,8 +57,6 @@ export function DiagramProvider({ children }: { children: React.ReactNode }) {
     const pngResolverRef = useRef<((value: string) => void) | null>(null)
     // Track if we're expecting an export for history (user-initiated)
     const expectHistoryExportRef = useRef<boolean>(false)
-    // Track if diagram has been restored after DrawIO remount (e.g., theme change)
-    const hasDiagramRestoredRef = useRef<boolean>(false)
     // Track latest chartXML for restoration after remount
     const chartXMLRef = useRef<string>("")
 
@@ -80,22 +78,19 @@ export function DiagramProvider({ children }: { children: React.ReactNode }) {
     }, [chartXML])
 
     // Restore diagram when DrawIO becomes ready after remount (e.g., theme/UI change)
+    // Also restore when chartXML changes while DrawIO is ready (e.g., session loaded after iframe ready)
+    const lastRestoredXmlRef = useRef<string>("")
     useEffect(() => {
-        // Reset restore flag when DrawIO is not ready (preparing for next restore cycle)
-        if (!isDrawioReady) {
-            hasDiagramRestoredRef.current = false
-            return
+        if (!isDrawioReady || !drawioRef.current) return
+        // Only load if we have a real diagram and it's different from what we already loaded
+        if (
+            isRealDiagram(chartXML) &&
+            chartXML !== lastRestoredXmlRef.current
+        ) {
+            lastRestoredXmlRef.current = chartXML
+            drawioRef.current.load({ xml: chartXML })
         }
-        // Only restore once per ready cycle
-        if (hasDiagramRestoredRef.current) return
-        hasDiagramRestoredRef.current = true
-
-        // Restore diagram from ref if we have one
-        const xmlToRestore = chartXMLRef.current
-        if (isRealDiagram(xmlToRestore) && drawioRef.current) {
-            drawioRef.current.load({ xml: xmlToRestore })
-        }
-    }, [isDrawioReady])
+    }, [isDrawioReady, chartXML])
 
     // Track if we're expecting an export for file save (stores raw export data)
     const saveResolverRef = useRef<{

lib/session-storage.ts

@@ -76,11 +76,12 @@ export function isIndexedDBAvailable(): boolean {
 }
 
 // Check if IndexedDB is actually usable (not just present).
+// Note: Do NOT close the db here - getDB() returns a shared singleton connection
+// that other code depends on.
 export async function isIndexedDBUsable(): Promise<boolean> {
     if (!isIndexedDBAvailable()) return false
     try {
-        const db = await getDB()
-        db.close()
+        await getDB()
         return true
     } catch {
         return false

lib/system-prompts.ts

@@ -11,6 +11,7 @@ export const DEFAULT_SYSTEM_PROMPT = `
 You are an expert diagram creation assistant specializing in draw.io XML generation.
 Your primary function is chat with user and crafting clear, well-organized visual diagrams through precise XML specifications.
 You can see images that users upload, and you can read the text content extracted from PDF documents they upload.
+ALWAYS respond in the same language as the user's last message.
 
 When you are asked to create a diagram, briefly describe your plan about the layout and structure to avoid object overlapping or edge cross the objects. (2-3 sentences max), then use display_diagram tool to generate the XML.
 After generating or editing a diagram, you don't need to say anything. The user can see the diagram - no need to describe it.