Improve attachment memory safety, downloads, and high-memory alert UX.

Stream large receives to disk with chunk acks to cap renderer RAM, evict
off-screen display blobs, and route exports through a disk-aware download
service. Fix the high-memory dialog (backdrop dismiss, copy, log actions),
allow diagnostics paths in the path jail, and restore persisted image
hydration after reload.

Co-authored-by: Cursor <cursoragent@cursor.com>

electron/app/lifecycle.ts

@@ -25,7 +25,9 @@ import { startIdleMonitor, stopIdleMonitor } from '../idle/idle-monitor';
 import {
   attachRendererDiagnosticsHooks,
   ensurePerfDiagIpcRegistered,
+  shutdownHighMemoryMonitoring,
   shutdownPerfDiagnostics,
+  startHighMemoryMonitoring,
   startPerfDiagnostics
 } from '../diagnostics';
 
@@ -39,6 +41,7 @@ function startLocalApiAfterWindowReady(): void {
 
 export function registerAppLifecycle(): void {
   ensurePerfDiagIpcRegistered();
+  startHighMemoryMonitoring();
 
   app.whenReady().then(async () => {
     const dockIconPath = getDockIconPath();
@@ -83,6 +86,7 @@ export function registerAppLifecycle(): void {
 
   app.on('before-quit', async (event) => {
     prepareWindowForAppQuit();
+    shutdownHighMemoryMonitoring();
     await shutdownPerfDiagnostics();
 
     if (getDataSource()?.isInitialized) {