There's \Symfony\Component\HttpFoundation\Session\SessionInterface::isStarted() in every request (even in tests) now
There is isStarted(), but it does not really tell if the session is lazy started.
change was commited to 8.6
https://git.drupalcode.org/project/drupal/-/commit/c811241f69bf75379b19d...
This is a link to the same revert commit I mentioned in #5 that reverts the change mentioned in #4, back ported to the 8.6 branch.
I believe #5 is still valid and relevant, so I replied for clarity. But I won't reopen, since I don't really know if anyone needs this.
Pretty cool that Vue.js author wrote comment on this issue (#45).
Overall, I feel that the situation with Drupal is very much similar to that of Wordrpess: the team already has investment in React
Or is it?
I don't know that Drupal has made a large investment in React, but large companies such as Acquia might have a large investment. Just look at the latest blog post of Dries:
https://dri.es/the-evolution-of-acquia-product-strategy
Specifically the picture at the bottom is worth a thousand words:
Β―\_(γ)_/Β―