Scope docs checkpoint tracker to checklist items after the Checkpoint heading

[Copilot]

The docs progress tracker currently counts every task-list item on a page, including non-checkpoint lists. This change narrows tracking to checklist items that appear after the page’s Checkpoint heading, so progress reflects checkpoint completion only.

• Tracker scope

  • Added a getCheckpointItems(page) selector that:
    • finds the first heading matching Checkpoint (with optional ✅ prefix)
    • returns only li.task-list-item nodes that follow that heading in document order
  • initPage now initializes state from this scoped list instead of all task-list items on the page.

• Behavioral impact

  • Progress bar, completion state, and “all checkpoints complete” banner now ignore pre-checkpoint checklists.
  • Pages without a Checkpoint heading are intentionally skipped by the tracker.

function getCheckpointItems(page) {
  var checkpointTitle = null;
  var headings = page.querySelectorAll('h1, h2, h3, h4, h5, h6');
  Array.prototype.some.call(headings, function (heading) {
    if (/^✅?\s*checkpoint$/i.test(heading.textContent.trim())) {
      checkpointTitle = heading;
      return true;
    }
    return false;
  });
  if (!checkpointTitle) return [];

  return Array.from(page.querySelectorAll('li.task-list-item')).filter(function (li) {
    return checkpointTitle.compareDocumentPosition(li) & Node.DOCUMENT_POSITION_FOLLOWING;
  });
}