support locally downloading attachments

js/src/electron.d.ts

@@ -44,6 +44,9 @@ declare global {
       fetchMetadata: (url: string) => Promise<LinkMetadata | null>;
       openExternal: (url: string) => Promise<void>;
     };
+    electronAttachment: {
+      download: (url: string, filename?: string) => void;
+    };
     electronApp: {
       setDockBadge: (count: number) => void;
     };

js/src/features/attachments/attachment-lightbox.tsx

@@ -49,15 +49,6 @@ function formatSize(bytes?: number): string | null {
   return `${(bytes / (1024 * 1024)).toFixed(1)} MB`;
 }
 
-function downloadFromUrl(url: string, filename: string) {
-  const a = document.createElement("a");
-  a.href = url;
-  a.download = filename;
-  document.body.appendChild(a);
-  a.click();
-  document.body.removeChild(a);
-}
-
 export function AttachmentLightbox({
   items,
   openIndex,
@@ -104,7 +95,7 @@ export function AttachmentLightbox({
 
   const handleDownload = () => {
     if (!current || !url || current.source.kind !== "remote") return;
-    downloadFromUrl(url, current.filename);
+    window.electronAttachment.download(url, current.filename);
   };
 
   const handleRemove = () => {

js/src/features/particles/particle-attachments.tsx

@@ -65,12 +65,7 @@ function ImageAttachment({
 
   const handleDownload = (e: React.MouseEvent) => {
     e.stopPropagation();
-    const a = document.createElement("a");
-    a.href = url;
-    a.download = particle.properties.filename;
-    document.body.appendChild(a);
-    a.click();
-    document.body.removeChild(a);
+    window.electronAttachment.download(url, particle.properties.filename);
   };
 
   return (
@@ -118,12 +113,7 @@ function FileAttachment({
   const handleDownload = (e: React.MouseEvent) => {
     e.stopPropagation();
     if (!url) return;
-    const a = document.createElement("a");
-    a.href = url;
-    a.download = particle.properties.filename;
-    document.body.appendChild(a);
-    a.click();
-    document.body.removeChild(a);
+    window.electronAttachment.download(url, particle.properties.filename);
   };
 
   return (

js/src/main.ts

@@ -454,6 +454,28 @@ ipcMain.handle('link:open-external', async (_event, url: string) => {
   await shell.openExternal(url);
 });
 
+// --- Attachment download ---
+// Triggers a native download with save-as dialog. Cross-origin safe — unlike
+// the web `<a download>` hack, which is ignored for cross-origin URLs.
+ipcMain.on(
+  'attachment:download',
+  (event, payload: { url: string; filename?: string }) => {
+    const win = BrowserWindow.fromWebContents(event.sender);
+    if (!win) return;
+    const { url, filename } = payload ?? {};
+    if (typeof url !== 'string') return;
+    if (!url.startsWith('http://') && !url.startsWith('https://')) return;
+
+    const dlSession = win.webContents.session;
+    const onWillDownload = (_e: Electron.Event, item: Electron.DownloadItem) => {
+      if (filename) item.setSaveDialogOptions({ defaultPath: filename });
+      dlSession.removeListener('will-download', onWillDownload);
+    };
+    dlSession.on('will-download', onWillDownload);
+    win.webContents.downloadURL(url);
+  },
+);
+
 // This method will be called when Electron has finished
 // initialization and is ready to create browser windows.
 // Some APIs can only be used after this event occurs.

js/src/preload.ts

@@ -66,6 +66,11 @@ contextBridge.exposeInMainWorld('electronLink', {
   openExternal: (url: string) => ipcRenderer.invoke('link:open-external', url),
 });
 
+contextBridge.exposeInMainWorld('electronAttachment', {
+  download: (url: string, filename?: string) =>
+    ipcRenderer.send('attachment:download', { url, filename }),
+});
+
 contextBridge.exposeInMainWorld('electronApp', {
   setDockBadge: (count: number) => ipcRenderer.send('app:set-dock-badge', count),
 });