refactor: use singleton pattern for screenshot service

- Export screenshotService singleton instance instead of class
- Remove redundant instantiation in IPC handlers
- Align with project patterns (mcpService, searchService, etc.)
- Simplify IPC handler code

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/main/ipc.ts

@@ -54,7 +54,7 @@ import powerMonitorService from './services/PowerMonitorService'
 import { proxyManager } from './services/ProxyManager'
 import { pythonService } from './services/PythonService'
 import { FileServiceManager } from './services/remotefile/FileServiceManager'
-import { Screenshot } from './services/ScreenshotService'
+import { screenshotService } from './services/ScreenshotService'
 import { searchService } from './services/SearchService'
 import { SelectionService } from './services/SelectionService'
 import { registerShortcuts, unregisterAllShortcuts } from './services/ShortcutService'
@@ -612,34 +612,24 @@ export function registerIpc(mainWindow: BrowserWindow, app: Electron.App) {
     }
   })
 
-  // Screenshot service singleton for selection flow
-  let screenshotService: Screenshot | null = null
-
+  // Screenshot
   ipcMain.handle(IpcChannel.Screenshot_Capture, async (_event, fileName: string) => {
-    const service = new Screenshot()
-    return await service.capture(fileName)
+    return await screenshotService.capture(fileName)
   })
 
   ipcMain.handle(IpcChannel.Screenshot_CaptureWithSelection, async (_event, fileName: string) => {
-    if (!screenshotService) {
-      screenshotService = new Screenshot()
-    }
     return await screenshotService.captureWithSelection(fileName)
   })
 
   ipcMain.handle(
     IpcChannel.Screenshot_SelectionConfirm,
     async (_event, selection: { x: number; y: number; width: number; height: number }) => {
-      if (screenshotService) {
-        screenshotService.confirmSelection(selection)
-      }
+      screenshotService.confirmSelection(selection)
     }
   )
 
   ipcMain.handle(IpcChannel.Screenshot_SelectionCancel, async () => {
-    if (screenshotService) {
-      screenshotService.cancelSelection()
-    }
+    screenshotService.cancelSelection()
   })
 
   ipcMain.handle(IpcChannel.File_BinaryImage, fileManager.binaryImage.bind(fileManager))

src/main/services/ScreenshotService.ts

@@ -29,7 +29,7 @@ interface Rectangle {
   height: number
 }
 
-export class ScreenshotService {
+class ScreenshotService {
   private selectionWindow: BrowserWindow | null = null
   private screenshotBuffer: Buffer | null = null
   private screenshotData: string | null = null
@@ -176,7 +176,7 @@ export class ScreenshotService {
     }
   }
 
-  public confirmSelection(selection: Rectangle): void {
+  public async confirmSelection(selection: Rectangle): Promise<void> {
     if (!this.selectionPromise) {
       logger.warn('No active selection to confirm')
       return
@@ -189,7 +189,7 @@ export class ScreenshotService {
         status: 'error',
         message: 'Selection too small (minimum 10×10 pixels)'
       })
-      void this.cleanupSelection()
+      await this.cleanupSelection()
       return
     }
 
@@ -197,7 +197,7 @@ export class ScreenshotService {
     this.processSelection(selection)
   }
 
-  public cancelSelection(): void {
+  public async cancelSelection(): Promise<void> {
     if (!this.selectionPromise) {
       logger.warn('No active selection to cancel')
       return
@@ -208,7 +208,7 @@ export class ScreenshotService {
       status: 'cancelled',
       message: 'User cancelled selection'
     })
-    void this.cleanupSelection()
+    await this.cleanupSelection()
   }
 
   private async processSelection(selection: Rectangle): Promise<void> {
@@ -349,3 +349,5 @@ export class ScreenshotService {
     }
   }
 }
+
+export const screenshotService = new ScreenshotService()