Merge train: how does it handle hotfixes

I’ve read the docs. It gives “happy path” examples.

Here’s a scenario that comes up often:

  1. MR1 and MR2 are now in the queue
  2. MR3 is a hotfix and needs to go in ASAP
  3. MR3 is behind both 1 and 2
  4. MR3 has pass review but 1 and 2 are still ongoing
  5. MR3 needs to move into source now

How would merge train solve this.
And if MR3 does get in, would MR1 AND MR2 re-merge and restart its pipeline?

This would be the same for scenario where MR1 and MR2 are in the queue.

If MR2 is behind MR1 but if MR2 passed review quicker than MR1 how can MR2 jump the queue?