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/preload.ts

@@ -11,6 +11,7 @@ const AUTO_UPDATE_STATE_CHANGED_CHANNEL = 'auto-update-state-changed';
 const DEEP_LINK_RECEIVED_CHANNEL = 'deep-link-received';
 const WINDOW_STATE_CHANGED_CHANNEL = 'window-state-changed';
 const IDLE_STATE_CHANGED_CHANNEL = 'idle-state-changed';
+const HIGH_MEMORY_ALERT_PENDING_CHANNEL = 'high-memory-alert-pending';
 
 export interface LinuxScreenShareAudioRoutingInfo {
   available: boolean;
@@ -264,8 +265,23 @@ export interface ElectronAPI {
     detectedAt: number;
     peakWorkingSetKb: number;
     sessionId: string;
+    reason?: 'manual' | 'threshold';
   } | null>;
   acknowledgeHighMemoryAlert: () => Promise<boolean>;
+  exportHighMemoryDiagnostics: () => Promise<{
+    logFilePath: string;
+    detectedAt: number;
+    peakWorkingSetKb: number;
+    sessionId: string;
+    reason?: 'manual' | 'threshold';
+  }>;
+  onHighMemoryAlertPending: (listener: (alert: {
+    logFilePath: string;
+    detectedAt: number;
+    peakWorkingSetKb: number;
+    sessionId: string;
+    reason?: 'manual' | 'threshold';
+  }) => void) => () => void;
   showLogFileInFolder: (filePath: string) => Promise<{ shown: boolean; reason?: string }>;
   getAppDataPath: () => Promise<string>;
   openCurrentDataFolder: () => Promise<boolean>;
@@ -335,6 +351,7 @@ export interface ElectronAPI {
   grantPluginReadRoot: (rootPath: string) => Promise<boolean>;
   writeFile: (filePath: string, data: string) => Promise<boolean>;
   appendFile: (filePath: string, data: string) => Promise<boolean>;
+  appendFileBytes: (filePath: string, data: Uint8Array) => Promise<boolean>;
   saveFileAs: (defaultFileName: string, data: string) => Promise<{ saved: boolean; cancelled: boolean }>;
   saveExistingFileAs: (sourceFilePath: string, defaultFileName: string) => Promise<{ saved: boolean; cancelled: boolean }>;
   openFilePath: (filePath: string) => Promise<{ opened: boolean; reason?: string }>;
@@ -410,6 +427,23 @@ const electronAPI: ElectronAPI = {
   reportPerfDiagSample: (entry) => ipcRenderer.invoke('perf-diag-report', entry),
   getPendingHighMemoryAlert: () => ipcRenderer.invoke('get-pending-high-memory-alert'),
   acknowledgeHighMemoryAlert: () => ipcRenderer.invoke('acknowledge-high-memory-alert'),
+  exportHighMemoryDiagnostics: () => ipcRenderer.invoke('export-high-memory-diagnostics'),
+  onHighMemoryAlertPending: (listener) => {
+    const wrappedListener = (_event: Electron.IpcRendererEvent, alert: {
+      logFilePath: string;
+      detectedAt: number;
+      peakWorkingSetKb: number;
+      sessionId: string;
+    }) => {
+      listener(alert);
+    };
+
+    ipcRenderer.on(HIGH_MEMORY_ALERT_PENDING_CHANNEL, wrappedListener);
+
+    return () => {
+      ipcRenderer.removeListener(HIGH_MEMORY_ALERT_PENDING_CHANNEL, wrappedListener);
+    };
+  },
   showLogFileInFolder: (filePath) => ipcRenderer.invoke('show-log-file-in-folder', filePath),
   getAppDataPath: () => ipcRenderer.invoke('get-app-data-path'),
   openCurrentDataFolder: () => ipcRenderer.invoke('open-current-data-folder'),
@@ -478,6 +512,7 @@ const electronAPI: ElectronAPI = {
   grantPluginReadRoot: (rootPath) => ipcRenderer.invoke('grant-plugin-read-root', rootPath),
   writeFile: (filePath, data) => ipcRenderer.invoke('write-file', filePath, data),
   appendFile: (filePath, data) => ipcRenderer.invoke('append-file', filePath, data),
+  appendFileBytes: (filePath, data) => ipcRenderer.invoke('append-file-bytes', filePath, data),
   saveFileAs: (defaultFileName, data) => ipcRenderer.invoke('save-file-as', defaultFileName, data),
   saveExistingFileAs: (sourceFilePath, defaultFileName) => ipcRenderer.invoke('save-existing-file-as', sourceFilePath, defaultFileName),
   openFilePath: (filePath) => ipcRenderer.invoke('open-file-path', filePath),