Mwenenzi, do you have any authority (law, regulation, staff policy statement, etc.) for the proposition that US law and regulation does not apply to a ticket bought elsewhere for travel to/from/via the US? I believe you're mistaken. I see no such statement anywhere in applicable DOT rules. Indeed, I see statements precisely the opposite.

Often1 and Moa999, thanks the thoughts. I agree that it's time to contact CX, which is why I did so yesterday. Often1, you're right that I haven't said much in this thread about what I want for a result, but I feel that's my prerogative. Clearly my discussions with CX will be different, as I need to tell them exactly what outcome I seek (and I have done exactly that). Meanwhile, anyone similarly situated, in case of future cancellation or significant schedule change, can look to this thread for insights into passengers' rights in this situation. What I ultimately choose to do is of lesser interest to others, I would think. But clearly I'm thinking about refund rights, not just reroute rights, and I'm thinking about that because it's a potentially-desirable outcome under these circumstances -- albeit of course more desirable if the refund is substantial and less so if the refund is zero or tiny; hence the need to try to figure out how the refund would be, and should be, calculated.