COVID can be asymptotic for long periods. This is the whole point for such systems to exist in the first place.

Yes, and you reveal your keys for the past when you are diagnosed, and then you go inside, stay inside, and do not reveal any further keys.

This is not useful for stalking.

Sure it is, you just need imagination. Say that you are a stalker, you (or someone delegated by you) passed near your target and got h(daykey, time), your target happens to go to the hospital for covid a while after, so you have the daykey of your target for multiple days and all of their h(day, time). You detect that it was your target that went into the hospital because one of their h(daykey, time) matches with the one that you have stored, in addition you know if your target passed nearby you/one of your friends/one of the locations where you have put some cheap bluetooth phones and the exact day and time that this happened. Intentionally infecting the target will covid will help this whole thing but it is not necessary.

This is just in no way a realistic attack scenario. It gains you nearly nothing for a massive amount of work.

You said that it can't be used for stalking. I said that it can and that it is difficult rather than impossible.

Instead of wasting everyone's time arguing pointless semantics, have you considered actually engaging in constructive discussion?

You really should stop blaming others for your own failure to properly convey what you mean.