changeContent breaks links

[massette]

Describe the bug Concurrent calls to <content-element>.changeContent permanently remove all event handlers from the element.

To Reproduce Add the following passage to a story and click the cycling link.

[JavaScript]
const body = document.querySelector("body-content");

window.addEventListener("click", () => {
    body.changeContent(() => {});
});

[continue]
{cycling link, choices: ["A", "B", "C"]}

[[This link will break->Other Passage]]

Expected behavior Event handlers are consistently restored after changeContent triggers a transition, regardless of the state of the page when it is called.

Stories and screenshots changeContent-issue.zip

Environment Problem observed on Windows 11 version 23H2 in Microsoft Edge version 128.0.2739.79.

[david-donachie]

As described on the Twine Discord, this looks like a race condition between two instances of changeContent(), one triggered by the cycling link, one by the user-added listener.

The sequence seems to be:

• The user clicks the link
• The cycling-link triggers changeContent() moving the live elements off-screen and replacing them with a static copy without event handlers
• The user-added event listener calls changeContent() moving the static HTML elements (without listeners) off-screen to it's own buffer
• The first changeContent() resolves, moving the original elements back on-screen
• The second changeContent() resolves, moving the handler-less copy back on-screen
• Now event handlers on elements are broken

It feels like either changeContent() needs a queue, or multiple instances called on the same element need a way to share the off-screen buffer rather than recreating it.