Clipboard API Ctrl+V double-paste repro (SVRN-1769)

Each target below registers a Ctrl+V keydown handler that calls preventDefault() on the keydown and then reads the clipboard via navigator.clipboard.readText(), appending the result to the target with the prefix [readText]. This mirrors how xterm.js handles paste in the VS Code Web / Codespaces integrated terminal.

The three targets differ only in their paste event handler:

• none: no paste handler.
• noPreventDefault: paste handler appends clipboardData.getData('text/plain') with prefix [paste]; does NOT call preventDefault.
• preventDefault: same handler, but calls preventDefault on the paste event.

Expected post-fix behavior, after a single Ctrl+V on each target with the source text PASTE_ME on the clipboard:

• none: target contains exactly [readText] PASTE_ME.
• noPreventDefault: same.
• preventDefault: same.

Pre-fix, the surrogate also synthesizes a paste event after the clipboard permission is granted. That synthesized event runs the page's paste handler and, unless the page calls preventDefault on it, also performs the browser's default paste action (inserting the text into the focused contenteditable). So pre-fix you'd see PASTE_ME appearing twice or three times depending on which target.

Source to copy from: Focus source

Focus none Focus noPreventDefault Focus preventDefault Clear all Report Results