Add clipboard utility to copy text temporarily

Co-authored-by: trevor-signal <131492920+trevor-signal@users.noreply.github.com>

ts/background.preload.ts

@@ -760,6 +760,8 @@ export async function startApp(): Promise<void> {
 
         flushMessageCounter();
 
+        window.SignalClipboard.clearIfNeeded();
+
         // Hangup active calls
         calling.hangupAllCalls({
           excludeRinging: true,

ts/components/PreferencesLocalBackups.dom.tsx

@@ -35,6 +35,7 @@ import type {
 } from '../util/os/promptOSAuthMain.main.js';
 import { ConfirmationDialog } from './ConfirmationDialog.dom.js';
 import { AxoButton } from '../axo/AxoButton.dom.js';
+import { SECOND } from '../util/durations/constants.std.js';
 
 const { noop } = lodash;
 
@@ -275,7 +276,7 @@ function LocalBackupsBackupKeyViewer({
   const onCopyBackupKey = useCallback(
     async function handleCopyBackupKey(e: React.MouseEvent) {
       e.preventDefault();
-      await window.navigator.clipboard.writeText(backupKey);
+      await window.SignalClipboard.copyTextTemporarily(backupKey, 45 * SECOND);
       showToast({ toastType: ToastType.CopiedBackupKey });
     },
     [backupKey, showToast]

ts/window.d.ts

@@ -192,6 +192,12 @@ declare global {
     // TODO DESKTOP-4801
     SignalContext: SignalContextType;
 
+    SignalClipboard: {
+      clear: () => void;
+      clearIfNeeded: () => void;
+      copyTextTemporarily: (text: string, clearAfterMs: number) => void;
+    };
+
     // Used only in preload to calculate load time
     preloadCompileStartTime: number;
     preloadStartTime: number;

ts/windows/clipboard.dom.ts

@@ -0,0 +1,36 @@
+// Copyright 2025 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import { clipboard } from 'electron';
+
+let doesClipboardNeedClearing = false;
+
+function clearClipboard(): void {
+  clipboard.clear('clipboard');
+
+  // clipboard.clear is not reliable on Linux, so we actually have to overwrite it
+  if (window.Signal.OS.isLinux()) {
+    clipboard.writeText(' ');
+  }
+
+  doesClipboardNeedClearing = false;
+}
+
+function clearClipboardIfNeeded(): void {
+  if (doesClipboardNeedClearing) {
+    clearClipboard();
+  }
+}
+
+function copyTextTemporarily(text: string, clearAfterMs: number): void {
+  clipboard.writeText(text);
+  doesClipboardNeedClearing = true;
+
+  setTimeout(() => clearClipboard(), clearAfterMs);
+}
+
+window.SignalClipboard = {
+  clearIfNeeded: clearClipboardIfNeeded,
+  clear: clearClipboard,
+  copyTextTemporarily,
+};

ts/windows/main/phase2-dependencies.preload.ts

@@ -15,6 +15,7 @@ import {
   DRAFT_PATH,
 } from '../../util/basePaths.preload.js';
 import { SignalContext } from '../context.preload.js';
+import '../clipboard.dom.js';
 
 initializeLogging();