javascript:(function(){

  /* -------------------------------------------------
     STEP 1 — USER CLICKS PARENT CHAT CONTAINER
  ------------------------------------------------- */

  alert("Click the chat container you want to start from.");

  function handler(ev) {
    ev.preventDefault();
    ev.stopPropagation();

    const start = ev.target;
    document.removeEventListener('click', handler, true);

    /* -------------------------------------------------
       STEP 2 — FIX OVERFLOW FROM CLICKED ELEMENT UPWARD
    ------------------------------------------------- */

    let el = start;
    while (el && el !== document.documentElement) {
      el.style.setProperty('overflow','visible','important');
      el.style.setProperty('overflow-y','visible','important');
      el.style.setProperty('overflow-x','visible','important');
      el.style.setProperty('max-height','none','important');
      el.style.setProperty('height','auto','important');
      el.style.setProperty('max-width','none','important');
      el.style.setProperty('width','auto','important');
      el = el.parentElement;
    }

    /* -------------------------------------------------
       STEP 3 — ASK WHICH MESSAGE NUMBER TO KEEP
    ------------------------------------------------- */

    let n = prompt("Which message number (1-indexed) should remain?");
    if (!n) return;

    n = parseInt(n, 10);
    if (!n) return;

    const msgs = Array.from(document.querySelectorAll('[data-message-id]'));

    if (n < 1 || n > msgs.length) {
      alert("Invalid index");
      return;
    }

    /* -------------------------------------------------
       STEP 4 — REMOVE ALL OTHER MESSAGES
    ------------------------------------------------- */

    msgs.forEach((msg, i) => {
      if (i !== (n - 1)) msg.remove();
    });

    msgs[n - 1].classList.add("target-element-e");

    const targets = document.querySelectorAll('.target-element-e');
    if (!targets.length) return;

    /* -------------------------------------------------
       STEP 5 — MARK TARGET DESCENDANTS & ANCESTORS
    ------------------------------------------------- */

    targets.forEach(target => {

      // mark descendants
      target.querySelectorAll('*').forEach(child =>
        child.classList.add('target-element-e')
      );

      // mark ancestors
      let el2 = target;
      while (el2) {
        el2.classList.add('target-element-e');
        el2 = el2.parentElement;
      }
    });

    /* -------------------------------------------------
       STEP 6 — HIDE EVERYTHING NOT MARKED
    ------------------------------------------------- */

    document.querySelectorAll('*').forEach(el3 => {
      if (!el3.classList.contains('target-element-e')) {
        el3.style.display = 'none';
      }
    });

  }

  // Capture NEXT click
  document.addEventListener('click', handler, true);

})();