I mentioned "relevant caselaw" to head off comments exactly like yours.

There was a few clear SCOTUS decisions on what limits there exist on 1st amendment, and movement limits weren't in there

There are more than a few decisions that would appear to bear at least indirectly on this situation which can help us guess what the outcome would be. In particular, the "clear and present danger" standard would probably apply; since one could tie assembly to disease transmission, a highly infectious disease would seem to qualify.

Another area that speech has been restricted has been around espionage and wartime; it's clear that during wartime, our ability to speak becomes much more restricted, at least partially for security reasons. Again, the practical reason for this is that war can be an existential risk for a country, and generally, people are more than willing to give up their rights temporarily to avoid the risk of their entire nation being wiped out.

So, while I agree (to my limited knowledge; I'm just a speculating engineer) that there is no direct case law that bears on this, I do feel that my predictions on which side the SC would fall (unless the court was packed with Scalias) are reasonable.

There is little more for me to add so I think I will terminate my participation in this subthread.

>A conditional right is no right at all.

This is what you stated, and now you are agreeing that there are conditions. If you now agree that there are conditions that these rights can be applied, I believe an actual pandemic would be reasonable as a condition to the first amendment.