How do you avoid this? It's a particular kind of institutional trickery that may not even be intentional but is very frustrating.
So there is some room for negotiation, although some things aren't negotiable for them. I've often had a non-compete clause of some sort in my contract, and I've always been able to get its scope reduced, but mever been able to get it dropped entirely. But if you ask up front about it, it's also to their benefit to be honest about it, because hiring you and then having you quit at the last moment because of their lie is not good for them either
The other option is to get the contract signed, or at least seen, before you quit your previous job. If it's a job for which you need to move and dramatically change your life, then you should definitely get some hard commitments from them before you do anything drastic.
And yes you can move on, but you're still in an unnecessary position (looking for work while not employed) through no fault of your own.
Then I got radio silence, could see all the checks passed on their end. Didn't end up signing, kept my current job.
Glad I refused. I don't want to work for any company that tries this bullshit.
And even with such an agreement, they might still ask you to sign something on day one. If you don't sign it, they may very well decided to "terminate the agreement" on day one.