I think you're right that the loss of an SSBN or a carrier group leads to escalation. As you say, both of those are counterforce strikes that directly harm the nation's ability to prosecute a war as well as harming the deterrent capacity. The assets are just too important. That said, I think an SSN/hunter-killer submarine could be lost without necessarily escalating in the same way.Is it really just tactical to use a nuclear ASM or depth bomb to destroy a CV or SSBN? CVBGs were so important to NATO that I think they’d rather have lost a quarter of Bavaria than the Nimitz. Destroying an SSBN is a counterforce strike. Maybe a nuclear ASROC fired in self-defence against an SSN shadowing a carrier would be okay. But nukes at sea causing unacceptable losses of high-value assets could cause escalation as a sort of ‘firebreak’: too much has been lost, so desperate measures must be taken to preserve what’s left, before it’s too late.
So maybe 1 kt-range battlefield tacnukes are less likely to cause escalation. They’re devastating in built up areas, but in natural terrain the area denial, morale-reducing and C3I-disrupting effects might’ve been greater than the actual destruction of troops and vehicles.
On the subkect of small yield tactical weapons, I can see them being used as glorified demolition charges to block strategic passes or destroy critical infrastructure, like bridges, road junctions, and maybe hardened military facilities that would be useful to an invading force as an army retreats. You could also use them to destroy dams or levees to flood the area you're leaving if you really want to reck it. But in all of these cases the nukes are just a way of saving time and effort on something you could achieve with normal tools and weapons. I don't think escalation is locked in, maybe not even likely, until you start destroying significant and important military and civilian assets because it forces your opponent to escalate to protect their remaining assets and use them before they lose the ability.