Problem with Scenario 1:

1. Given we can be pretty sure Chinese authorities would have already done the above testing, it’s a reasonable assumption we would know the results if it turned up anything that cleared WIV.

This is an excellent point and one I hadn't considered. Indeed, if they had the evidence that absolved them from all responsibility, they would share it.

2. Why was there no outbreak at the site of the infection? It’s possible that the infected humans living in the immediate vicinity of the cave may have already developed an immunity (which could be easily checked through an antibody test) but there still should have been some sign of contagion in more populous areas of Yunnan.

Another excellent point. Again, if locals had developed this immunity, that would be easy to prove and it would also be shared.

Conclusion

It's unlikely, but it's not impossible. If there was a 'patient-zero' and that person travelled directly from the cave site to Wuhan, 1000km away, probably by car, thereby not infecting anyone else, then stayed in Wuhan for two weeks or more ... it's theoretically doable.
On the positive side, being a small probability field, it's easy to prove one way or the other: trace the shit out of it.
If you're a totalitarian regime that's big on surveillance, you're tooled up - it's not like you're gonna have privacy rights qualms.
The first reported case is mid-Nov. We know it's highly contagious - the 'lying dormant for years' theory doesn't make sense - this virus hit the ground running. There'd have been a period where people wouldn't have twigged - it's similar to the flu - so you'd expect that - but it's explosive by nature - so maybe a month before that?
So go ahead - use your high-tech-totalitarianism to trace it back to those first cases - let's say it is mid-October (though i'd bow to the CCP's intel on that)- now you've got to the origin window within a week or two.

Cross reference that with those in close contact with bats at the Mojiang mine who travelled to Wuhan in that timeframe - bingo - you've got your origin. Case solved

Of course, we'll never see this logic used in any reporting.