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

@@ -11,10 +11,16 @@ import {
 } from "@/components/ui/resizable"
 import { useDiagram } from "@/contexts/diagram-context"
 import { i18n, type Locale } from "@/lib/i18n/config"
+import { isIndexedDBUsable } from "@/lib/session-storage"
 
 export default function Home() {
-    const { drawioRef, handleDiagramExport, onDrawioLoad, resetDrawioReady } =
+    const {
-        useDiagram()
+        drawioRef,
+        handleDiagramExport,
+        handleDiagramAutoSave,
+        onDrawioLoad,
+        resetDrawioReady,
+    } = useDiagram()
     const router = useRouter()
     const pathname = usePathname()
     // Extract current language from pathname (e.g., "/zh/about" → "zh")
@@ -26,6 +32,8 @@ export default function Home() {
     const [isLoaded, setIsLoaded] = useState(false)
     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",
     )
@@ -76,6 +84,11 @@ export default function Home() {
             setDrawioBaseUrl(`${window.location.origin}/drawio/index.html`)
         }
 
+        void (async () => {
+            const usable = await isIndexedDBUsable()
+            setCanPersist(usable)
+            setCanPersistChecked(true)
+        })()
         setIsLoaded(true)
     }, [pathname, router])
 
@@ -84,6 +97,17 @@ export default function Home() {
         onDrawioLoad()
     }, [onDrawioLoad])
 
+    const handleDrawioAutoSave = useCallback(
+        (data: { xml?: string }) => {
+            handleDiagramAutoSave(data)
+            // Only suppress modified state when persistence is available
+            if (canPersist) {
+                drawioRef.current?.status({ message: "", modified: false })
+            }
+        },
+        [canPersist, drawioRef, handleDiagramAutoSave],
+    )
+
     const handleDarkModeChange = () => {
         const newValue = !darkMode
         setDarkMode(newValue)
@@ -167,20 +191,32 @@ 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 ${isDrawioReady ? "" : "invisible absolute inset-0"}`}
                                 >
                                     <DrawIoEmbed
                                         key={`${drawioUi}-${darkMode}-${currentLang}-${isElectron}`}
                                         ref={drawioRef}
+                                        autosave
+                                        onAutoSave={handleDrawioAutoSave}
                                         onExport={handleDiagramExport}
                                         onLoad={handleDrawioLoad}
                                         baseUrl={drawioBaseUrl}
+                                        configuration={
+                                            canPersist
+                                                ? { confirmExit: false }
+                                                : undefined
+                                        }
                                         urlParameters={{
                                             ui: drawioUi,
                                             spin: false,
                                             libraries: false,
+                                            // Disable modified tracking only when persistence is available
+                                            ...(canPersist && {
+                                                modified: false,
+                                                keepmodified: false,
+                                            }),
                                             saveAndExit: false,
                                             noSaveBtn: true,
                                             noExitBtn: true,

components/chat-panel.tsx

@@ -137,26 +137,22 @@ export default function ChatPanel({
     const onFetchChart = (saveToHistory = true) => {
         return Promise.race([
             new Promise<string>((resolve) => {
-                if (resolverRef && "current" in resolverRef) {
+                resolverRef.current = resolve
-                    resolverRef.current = resolve
-                }
                 if (saveToHistory) {
                     onExport()
                 } else {
                     handleExportWithoutHistory()
                 }
             }),
-            new Promise<string>((_, reject) =>
+            new Promise<string>((_, reject) => {
-                setTimeout(
+                const currentResolver = resolverRef.current
-                    () =>
+                setTimeout(() => {
-                        reject(
+                    if (resolverRef.current === currentResolver) {
-                            new Error(
+                        resolverRef.current = null
-                                "Chart export timed out after 10 seconds",
+                    }
-                            ),
+                    reject(new Error("Chart export timed out after 10 seconds"))
-                        ),
+                }, 10000)
-                    10000,
+            }),
-                ),
-            ),
         ])
     }
 
@@ -677,7 +673,7 @@ export default function ChatPanel({
         // Debounce: save after 1 second of no changes
         localStorageDebounceRef.current = setTimeout(async () => {
             try {
-                if (messages.length > 0) {
+                if (messages.length > 0 || hasDiagramNow) {
                     const sessionData = await buildSessionData({
                         // Only capture thumbnail if there was a diagram AND this isn't a no-diagram session
                         withThumbnail: hasDiagramNow && !isNodiagramSession,
@@ -699,6 +695,7 @@ export default function ChatPanel({
             }
         }
     }, [
+        chartXML,
         messages,
         status,
         sessionIsAvailable,
@@ -729,7 +726,8 @@ export default function ChatPanel({
         const handleVisibilityChange = async () => {
             if (
                 document.visibilityState === "hidden" &&
-                messagesRef.current.length > 0
+                (messagesRef.current.length > 0 ||
+                    isRealDiagram(chartXMLRef.current))
             ) {
                 try {
                     // Attempt to save session - browser may not wait for completion

contexts/diagram-context.tsx

@@ -20,9 +20,10 @@ interface DiagramContextType {
     loadDiagram: (chart: string, skipValidation?: boolean) => string | null
     handleExport: () => void
     handleExportWithoutHistory: () => void
-    resolverRef: React.Ref<((value: string) => void) | null>
+    resolverRef: React.MutableRefObject<((value: string) => void) | null>
-    drawioRef: React.Ref<DrawIoEmbedRef | null>
+    drawioRef: React.MutableRefObject<DrawIoEmbedRef | null>
     handleDiagramExport: (data: any) => void
+    handleDiagramAutoSave: (data: { xml?: string }) => void
     clearDiagram: () => void
     saveDiagramToFile: (
         filename: string,
@@ -56,8 +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>("")
 
@@ -79,22 +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 || !drawioRef.current) return
-        if (!isDrawioReady) {
+        // Only load if we have a real diagram and it's different from what we already loaded
-            hasDiagramRestoredRef.current = false
+        if (
-            return
+            isRealDiagram(chartXML) &&
+            chartXML !== lastRestoredXmlRef.current
+        ) {
+            lastRestoredXmlRef.current = chartXML
+            drawioRef.current.load({ xml: chartXML })
         }
-        // Only restore once per ready cycle
+    }, [isDrawioReady, chartXML])
-        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])
 
     // Track if we're expecting an export for file save (stores raw export data)
     const saveResolverRef = useRef<{
@@ -267,6 +263,11 @@ export function DiagramProvider({ children }: { children: React.ReactNode }) {
         }
     }
 
+    const handleDiagramAutoSave = (data: { xml?: string }) => {
+        if (!data?.xml) return
+        setChartXML(data.xml)
+    }
+
     const clearDiagram = () => {
         const emptyDiagram = `<mxfile><diagram name="Page-1" id="page-1"><mxGraphModel><root><mxCell id="0"/><mxCell id="1" parent="0"/></root></mxGraphModel></diagram></mxfile>`
         // Skip validation for trusted internal template (loadDiagram also sets chartXML)
@@ -391,6 +392,7 @@ export function DiagramProvider({ children }: { children: React.ReactNode }) {
                 resolverRef,
                 drawioRef,
                 handleDiagramExport,
+                handleDiagramAutoSave,
                 clearDiagram,
                 saveDiagramToFile,
                 getThumbnailSvg,

lib/session-storage.ts

@@ -75,6 +75,19 @@ 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 {
+        await getDB()
+        return true
+    } catch {
+        return false
+    }
+}
+
 // CRUD Operations
 export async function getAllSessionMetadata(): Promise<SessionMetadata[]> {
     if (!isIndexedDBAvailable()) return []