fix(electron): override draw.io iframe beforeunload to allow window close (fixes #815)

The draw.io iframe registers a window.onbeforeunload handler that returns
a non-empty string whenever its internal editor.modified flag is true.
After the user edits text in a shape, that flag is set and never cleared.

Per Electron BrowserWindow docs, returning a non-void value from any
beforeunload handler in the page tree silently cancels the window close
without showing a dialog. This is what caused the X button (and Cmd+Q)
to do nothing for users who had typed in a shape.

Calling event.preventDefault() in will-prevent-unload tells Electron to
ignore the iframe's beforeunload return value and proceed with the close.
The host app already persists diagrams via autosave + visibilitychange,
so the prompt was unnecessary.

Verified by reproducing the bug, applying the fix, and re-testing.

app/[lang]/page.tsx

@@ -12,6 +12,7 @@ import {
 import { useDiagram } from "@/contexts/diagram-context"
 import { type DrawioTheme, isDrawioTheme } from "@/lib/drawio-themes"
 import { i18n, type Locale } from "@/lib/i18n/config"
+import { isIndexedDBUsable } from "@/lib/session-storage"
 
 export default function Home() {
     const {
@@ -32,6 +33,8 @@ 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",
     )
@@ -82,6 +85,11 @@ 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])
 
@@ -90,6 +98,13 @@ export default function Home() {
         onDrawioLoad()
     }, [onDrawioLoad])
 
+    const handleDrawioAutoSave = useCallback(
+        (data: { xml?: string }) => {
+            handleDiagramAutoSave(data)
+        },
+        [handleDiagramAutoSave],
+    )
+
     const handleDarkModeChange = () => {
         const newValue = !darkMode
         setDarkMode(newValue)
@@ -172,7 +187,7 @@ 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 ${isDrawioReady ? "" : "invisible absolute inset-0"}`}
                                 >
@@ -180,14 +195,24 @@ export default function Home() {
                                         key={`${drawioUi}-${darkMode}-${currentLang}-${isElectron}`}
                                         ref={drawioRef}
                                         autosave
-                                        onAutoSave={handleDiagramAutoSave}
+                                        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,

lib/session-storage.ts

@@ -58,6 +58,33 @@ interface ChatSessionDB extends DBSchema {
 
 // Database singleton
 let dbPromise: Promise<IDBPDatabase<ChatSessionDB>> | null = null
+const resetDBPromise = () => {
+    dbPromise = null
+}
+
+const isClosingError = (error: unknown): boolean => {
+    return (
+        error instanceof DOMException &&
+        error.name === "InvalidStateError" &&
+        /closing/i.test(error.message)
+    )
+}
+
+const withDB = async <T>(
+    action: (db: IDBPDatabase<ChatSessionDB>) => Promise<T>,
+): Promise<T> => {
+    try {
+        const db = await getDB()
+        return await action(db)
+    } catch (error) {
+        if (isClosingError(error)) {
+            resetDBPromise()
+            const db = await getDB()
+            return await action(db)
+        }
+        throw error
+    }
+}
 
 async function getDB(): Promise<IDBPDatabase<ChatSessionDB>> {
     if (!dbPromise) {
@@ -88,7 +115,23 @@ async function getDB(): Promise<IDBPDatabase<ChatSessionDB>> {
                     }
                 }
             },
+            terminated() {
+                resetDBPromise()
+            },
         })
+        dbPromise
+            .then((db) => {
+                db.onversionchange = () => {
+                    db.close()
+                    resetDBPromise()
+                }
+                db.onclose = () => {
+                    resetDBPromise()
+                }
+            })
+            .catch(() => {
+                resetDBPromise()
+            })
     }
     return dbPromise
 }
@@ -103,31 +146,46 @@ 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 []
     try {
-        const db = await getDB()
-        const tx = db.transaction(STORE_NAME, "readonly")
-        const index = tx.store.index("by-updated")
-        const metadata: SessionMetadata[] = []
+        return await withDB(async (db) => {
+            const tx = db.transaction(STORE_NAME, "readonly")
+            const index = tx.store.index("by-updated")
+            const metadata: SessionMetadata[] = []
 
-        // Use cursor to read only metadata fields (avoids loading full messages/XML)
-        let cursor = await index.openCursor(null, "prev") // newest first
-        while (cursor) {
-            const s = cursor.value
-            metadata.push({
-                id: s.id,
-                title: s.title,
-                createdAt: s.createdAt,
-                updatedAt: s.updatedAt,
-                messageCount: s.messages.length,
-                hasDiagram: !!s.diagramXml && s.diagramXml.trim().length > 0,
-                thumbnailDataUrl: s.thumbnailDataUrl,
-            })
-            cursor = await cursor.continue()
-        }
-        return metadata
+            // Use cursor to read only metadata fields (avoids loading full messages/XML)
+            let cursor = await index.openCursor(null, "prev") // newest first
+            while (cursor) {
+                const s = cursor.value
+                metadata.push({
+                    id: s.id,
+                    title: s.title,
+                    createdAt: s.createdAt,
+                    updatedAt: s.updatedAt,
+                    messageCount: s.messages.length,
+                    hasDiagram:
+                        !!s.diagramXml && s.diagramXml.trim().length > 0,
+                    thumbnailDataUrl: s.thumbnailDataUrl,
+                })
+                cursor = await cursor.continue()
+            }
+            return metadata
+        })
     } catch (error) {
         console.error("Failed to get session metadata:", error)
         return []
@@ -137,8 +195,9 @@ export async function getAllSessionMetadata(): Promise<SessionMetadata[]> {
 export async function getSession(id: string): Promise<ChatSession | null> {
     if (!isIndexedDBAvailable()) return null
     try {
-        const db = await getDB()
-        return (await db.get(STORE_NAME, id)) || null
+        return await withDB(async (db) => {
+            return (await db.get(STORE_NAME, id)) || null
+        })
     } catch (error) {
         console.error("Failed to get session:", error)
         return null
@@ -148,8 +207,9 @@ export async function getSession(id: string): Promise<ChatSession | null> {
 export async function saveSession(session: ChatSession): Promise<boolean> {
     if (!isIndexedDBAvailable()) return false
     try {
-        const db = await getDB()
-        await db.put(STORE_NAME, session)
+        await withDB(async (db) => {
+            await db.put(STORE_NAME, session)
+        })
         return true
     } catch (error) {
         // Handle quota exceeded
@@ -161,8 +221,9 @@ export async function saveSession(session: ChatSession): Promise<boolean> {
             await deleteOldestSession()
             // Retry once
             try {
-                const db = await getDB()
-                await db.put(STORE_NAME, session)
+                await withDB(async (db) => {
+                    await db.put(STORE_NAME, session)
+                })
                 return true
             } catch (retryError) {
                 console.error(
@@ -181,8 +242,9 @@ export async function saveSession(session: ChatSession): Promise<boolean> {
 export async function deleteSession(id: string): Promise<void> {
     if (!isIndexedDBAvailable()) return
     try {
-        const db = await getDB()
-        await db.delete(STORE_NAME, id)
+        await withDB(async (db) => {
+            await db.delete(STORE_NAME, id)
+        })
     } catch (error) {
         console.error("Failed to delete session:", error)
     }
@@ -191,8 +253,9 @@ export async function deleteSession(id: string): Promise<void> {
 export async function getSessionCount(): Promise<number> {
     if (!isIndexedDBAvailable()) return 0
     try {
-        const db = await getDB()
-        return await db.count(STORE_NAME)
+        return await withDB(async (db) => {
+            return await db.count(STORE_NAME)
+        })
     } catch (error) {
         console.error("Failed to get session count:", error)
         return 0
@@ -202,14 +265,15 @@ export async function getSessionCount(): Promise<number> {
 export async function deleteOldestSession(): Promise<void> {
     if (!isIndexedDBAvailable()) return
     try {
-        const db = await getDB()
-        const tx = db.transaction(STORE_NAME, "readwrite")
-        const index = tx.store.index("by-updated")
-        const cursor = await index.openCursor()
-        if (cursor) {
-            await cursor.delete()
-        }
-        await tx.done
+        await withDB(async (db) => {
+            const tx = db.transaction(STORE_NAME, "readwrite")
+            const index = tx.store.index("by-updated")
+            const cursor = await index.openCursor()
+            if (cursor) {
+                await cursor.delete()
+            }
+            await tx.done
+        })
     } catch (error) {
         console.error("Failed to delete oldest session:", error)
     }

lib/template-storage.ts

@@ -57,6 +57,33 @@ export function generateDefaultTitle(prompt: string): string {
 
 // Database singleton
 let dbPromise: Promise<IDBPDatabase<TemplateDB>> | null = null
+const resetDBPromise = () => {
+    dbPromise = null
+}
+
+const isClosingError = (error: unknown): boolean => {
+    return (
+        error instanceof DOMException &&
+        error.name === "InvalidStateError" &&
+        /closing/i.test(error.message)
+    )
+}
+
+const withDB = async <T>(
+    action: (db: IDBPDatabase<TemplateDB>) => Promise<T>,
+): Promise<T> => {
+    try {
+        const db = await getDB()
+        return await action(db)
+    } catch (error) {
+        if (isClosingError(error)) {
+            resetDBPromise()
+            const db = await getDB()
+            return await action(db)
+        }
+        throw error
+    }
+}
 
 async function getDB(): Promise<IDBPDatabase<TemplateDB>> {
     if (!dbPromise) {
@@ -74,7 +101,23 @@ async function getDB(): Promise<IDBPDatabase<TemplateDB>> {
                     }
                 }
             },
+            terminated() {
+                resetDBPromise()
+            },
         })
+        dbPromise
+            .then((db) => {
+                db.onversionchange = () => {
+                    db.close()
+                    resetDBPromise()
+                }
+                db.onclose = () => {
+                    resetDBPromise()
+                }
+            })
+            .catch(() => {
+                resetDBPromise()
+            })
     }
     return dbPromise
 }
@@ -94,9 +137,10 @@ export function isIndexedDBAvailable(): boolean {
 export async function getAllTemplates(): Promise<Template[]> {
     if (!isIndexedDBAvailable()) return []
     try {
-        const db = await getDB()
-        const templates = await db.getAll(STORE_NAME)
-        return sortTemplates(templates)
+        return await withDB(async (db) => {
+            const templates = await db.getAll(STORE_NAME)
+            return sortTemplates(templates)
+        })
     } catch (error) {
         console.error("Failed to get templates:", error)
         return []
@@ -106,8 +150,9 @@ export async function getAllTemplates(): Promise<Template[]> {
 export async function getTemplate(id: string): Promise<Template | null> {
     if (!isIndexedDBAvailable()) return null
     try {
-        const db = await getDB()
-        return (await db.get(STORE_NAME, id)) || null
+        return await withDB(async (db) => {
+            return (await db.get(STORE_NAME, id)) || null
+        })
     } catch (error) {
         console.error("Failed to get template:", error)
         return null
@@ -137,8 +182,9 @@ export async function createTemplate(
     }
 
     try {
-        const db = await getDB()
-        await db.put(STORE_NAME, template)
+        await withDB(async (db) => {
+            await db.put(STORE_NAME, template)
+        })
         return template
     } catch (error) {
         console.error("Failed to create template:", error)
@@ -152,19 +198,20 @@ export async function updateTemplate(
 ): Promise<Template | null> {
     if (!isIndexedDBAvailable()) return null
     try {
-        const db = await getDB()
-        const existing = await db.get(STORE_NAME, id)
-        if (!existing) return null
+        return await withDB(async (db) => {
+            const existing = await db.get(STORE_NAME, id)
+            if (!existing) return null
 
-        const updated: Template = {
-            ...existing,
-            ...updates,
-            id: existing.id,
-            createdAt: existing.createdAt,
-            updatedAt: Date.now(),
-        }
-        await db.put(STORE_NAME, updated)
-        return updated
+            const updated: Template = {
+                ...existing,
+                ...updates,
+                id: existing.id,
+                createdAt: existing.createdAt,
+                updatedAt: Date.now(),
+            }
+            await db.put(STORE_NAME, updated)
+            return updated
+        })
     } catch (error) {
         console.error("Failed to update template:", error)
         return null
@@ -174,8 +221,9 @@ export async function updateTemplate(
 export async function deleteTemplate(id: string): Promise<boolean> {
     if (!isIndexedDBAvailable()) return false
     try {
-        const db = await getDB()
-        await db.delete(STORE_NAME, id)
+        await withDB(async (db) => {
+            await db.delete(STORE_NAME, id)
+        })
         return true
     } catch (error) {
         console.error("Failed to delete template:", error)
@@ -189,24 +237,25 @@ export async function duplicateTemplate(
 ): Promise<Template | null> {
     if (!isIndexedDBAvailable()) return null
     try {
-        const db = await getDB()
-        const existing = await db.get(STORE_NAME, id)
-        if (!existing) return null
+        return await withDB(async (db) => {
+            const existing = await db.get(STORE_NAME, id)
+            if (!existing) return null
 
-        const now = Date.now()
-        const duplicate: Template = {
-            ...existing,
-            id: nanoid(),
-            title: `${existing.title} ${copySuffix}`,
-            createdAt: now,
-            updatedAt: now,
-            clickCount: 0,
-            runCount: 0,
-            lastUsedAt: 0,
-            pinned: false,
-        }
-        await db.put(STORE_NAME, duplicate)
-        return duplicate
+            const now = Date.now()
+            const duplicate: Template = {
+                ...existing,
+                id: nanoid(),
+                title: `${existing.title} ${copySuffix}`,
+                createdAt: now,
+                updatedAt: now,
+                clickCount: 0,
+                runCount: 0,
+                lastUsedAt: 0,
+                pinned: false,
+            }
+            await db.put(STORE_NAME, duplicate)
+            return duplicate
+        })
     } catch (error) {
         console.error("Failed to duplicate template:", error)
         return null
@@ -218,12 +267,13 @@ export async function duplicateTemplate(
 export async function incrementClickCount(id: string): Promise<void> {
     if (!isIndexedDBAvailable()) return
     try {
-        const db = await getDB()
-        const template = await db.get(STORE_NAME, id)
-        if (!template) return
-        template.clickCount += 1
-        template.updatedAt = Date.now()
-        await db.put(STORE_NAME, template)
+        await withDB(async (db) => {
+            const template = await db.get(STORE_NAME, id)
+            if (!template) return
+            template.clickCount += 1
+            template.updatedAt = Date.now()
+            await db.put(STORE_NAME, template)
+        })
     } catch (error) {
         console.error("Failed to increment click count:", error)
     }
@@ -232,14 +282,15 @@ export async function incrementClickCount(id: string): Promise<void> {
 export async function incrementRunCount(id: string): Promise<void> {
     if (!isIndexedDBAvailable()) return
     try {
-        const db = await getDB()
-        const template = await db.get(STORE_NAME, id)
-        if (!template) return
-        const now = Date.now()
-        template.runCount += 1
-        template.lastUsedAt = now
-        template.updatedAt = now
-        await db.put(STORE_NAME, template)
+        await withDB(async (db) => {
+            const template = await db.get(STORE_NAME, id)
+            if (!template) return
+            const now = Date.now()
+            template.runCount += 1
+            template.lastUsedAt = now
+            template.updatedAt = now
+            await db.put(STORE_NAME, template)
+        })
     } catch (error) {
         console.error("Failed to increment run count:", error)
     }
@@ -372,8 +423,9 @@ export async function importTemplates(
             pinned: typeof t.pinned === "boolean" ? t.pinned : false,
         }
         try {
-            const db = await getDB()
-            await db.put(STORE_NAME, newTemplate)
+            await withDB(async (db) => {
+                await db.put(STORE_NAME, newTemplate)
+            })
             existingKeys.add(key)
             imported++
         } catch (error) {