Ah yes, thanks. I must have misread your comment.
In that case, it sounds like you're asking about whether a hard forking consensus change could be deployed through sentinels. It's a very interesting question, actually! I had considered deploying a fork through the method of sentinels to be safer in some ways, because it removes the risk of soft fork bugs creating problems for Core users. But I think that if a fork is deployed through sentinels, it's only possible to be a soft fork and couldn't possibly be a hard fork. I consider this to be a feature.
The more I consider it, the more I think it would be impossible to outright change the consensus methodology to something other than PoW via sentinels. The reason being that sentinels can only tell nodes which previously valid transactions are now invalid. There's no way to make Core accept previously invalid transactions that are now valid.
I would be interested in other places a soft fork method like this has been discussed, if you have any references (no pressure, I'm sure that's a very deep cut).
I'm sure that's a very deep cut
Yeah. Of the ones I distinctly remember, I recall some reddit posts by Greg Maxwell back during the segwit activation days, which I cannot find because because reddit search sucks and I neglected to favorite them at the time. So they might be lost to history. But Greg was discussing how miners could run some soft fork software next to Bitcoin Core, and it would use the soft fork software to validate incoming blocks, and use Bitcoin Core to validate outgoing blocks (to ensure that the blocks would be accepted by non-upgraded miners).
More recently, there was related discussion prompted by the CTV activation debate in 2021. That might be easier to find, and more diverse discussion since many people took part in it. Jeremy had proposed using an alt-client to activate CTV, which was controversial in and of itself, aside from the proposed Speedy Trial activation mechanism.
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