There are always unique exceptions, even under the safe third country agreement. We always do a case-by-case assessment. We try not to have blanketed decision-making in an omnibus way.
The principles underlying the safe third country agreement promote the outcome you've just described, which is to say that, if you're safe in the country where you first arrived, we would prefer to have you make the asylum claim in that country, including people who first arrive in Canada.