Does this break cabotage?
 

I'm doing a US-Asia round trip in 3 days without going landside, just to enjoy the flights. Not by choice, but work obligations forcing me to otherwise waste the tickets.

Ticket 1: USA - YVR
Ticket 2: YVR - HAN (Cx)
Ticket 3: HAN - USA (JAL)

Am I safe if ticket 1 is a US carrier? Do I need to exit immigration at any point? Thanks.

I see no domestic flights by a foreign carrier. (I see no domestic flights at all).

And wouldn't it be an airline that's in trouble for violating cabotage regulations by selling a specific ticket, not a passenger?

Is there a different definition?

This is not what is generically referred to as cabotage and is covered by US law and DOT rules. You are flying round-trip to HAN.

While it is true that the violation is by the carrier, not the individual, it is the individual who would suffer as well were there a violation as the ticket(s) would be cancelled.and refunded.

the city pair points and length of journey can be a factor in determining cabotage if it's all foreign carriers transporting you

One common example is flying solely AC for USA-canada-different USA airport

One extreme example that keeps coming up is USA-ICN-Guam. Looks like the Korean airlines have good computers to detect such transits, even for separately purchased itineraries
See https://www.flyertalk.com/forum/30704622-post24.html

as for OP's question, I doubt he'll have a problem.
There's no cost benefit (and a huge time waster) to do a transpacific trip versus a 6hour domestic flight (eg EWR-LAX), compared to a potential cheaper but Canadian cabotage of 8hour (EWR-YUL-LAX on AC)

To be clear, if it were in OP's interests, he could purchase this routing on these carriers on a single ticket and not encounter any issues. Depending on whether the origination and termiantion "USA" are the same, this will be viewed as either a round-trip to HAN or an open jaw.

All of this presumes that by "USA" OP does not mean LAX on the outbound and GUM on the return.

Would be most helpful if OP would provide the "USA" locations for 100% certainty.

That's a modified sixth freedom issue, no? While it could be debated whether this falls under the definition of cabotage, I see nothing of that type in OP's plans - none of the flights begin and end in the same country.

Nothing is certain until OP provides the origin & destination airports. But, to be frank, it is almost certain as is. In fact, this routing could be booked on a single ticket (not that single vs. multiple tickets are dispositive).

Does CUN-ATL-MEX with Delta and Aeromexico on the same PNR break cabotage?

Would seem to depend on Mexico law, and the "freedoms" permitted, no?

No. Since one of the segments is on AM, there is no cabotage under the laws of any nation.

Why would this be enjoyable - even in business or first? I would spend a few days in HAN or change/cancel.

Cabotage Rules
 

I have a round trip ticket:
Kansas City-Seoul-Kansas City (UA)
* staying in Seoul for 3 months

Doing a side trip (round trip):
Seoul-Guam-Seoul (KE)
*staying in Guam 2 1/2 months

Is this considered cabotage?

No. Cabotage is when a foreign carrier flies passengers between a domestic origin and destination (O & D).

Each segment alone is not a domestic O & D.

And considering the MCI-ICN-GUM itinerary as a single trip, it is not a foreign carrier, KE, flying all of it. UA Is an American carrier, so no cabotage.