I exclusively move in a jj repo with `jj new` and `jj squash` or `jj squash --to <rev>` as appropriate. I've been using it 8+ hours daily for months and have never, ever even thought of having this issue.
And now people are saying it for jj.
Endless cycle it seems, with every new tool.
Thus, if you're worried about mutating existing commits, don't use it.
What exactly is so hard to understand here? You're not making the gotcha point you seem to think you are - it's not like it's some common command that is hyper-overloaded and has to be used specially.
Just another example of the usual HN skepticism that isn't even skepticism, it's just smug ignorance. It's so exhausting. But sure, the countless people that keep claiming its the single biggest tool improvement in some time are just idiots? suckers? hype-beasts? making it up? or what?
Like, the irony of you assuming that it must be as convoluted and hard to use as git is just... awesome. I love the Git defenders that literally can't fathom that there is actually a better mental model or simpler tool, and can't even be arsed to try it and see.
For example, I've configured it for me to make any commit by anyone else mutable regardless of branch:
[revset-aliases]
# To always consider changes by others immutable:
"immutable_heads()" = "builtin_immutable_heads() | (trunk().. & ~mine())"