My dog isn't sapient at all. He's quite sentient, though. Judging by the paper we shouldn't be killing octopuses at all, let alone inhumanely.
Dogs are more than sentient. Part of their behavior is learned, they have knowledge, experience, understanding, common sense (with both dogs and humans). No idea if insight has been studied in dogs specifically, but it isn't a human exclusive either (https://pubmed.ncbi.nlm.nih.gov/23231629/).
Which, I mean, they are. Here's a litmus test: Is that creature so simple that you (or a suitably skilled technologist) could build one? If so then it's not sentient/sapient/a person/something we shouldn't be mean to. If not then maybe we should pay it a little more respect.
Sapience was probably defined hoping to make it a human exclusive, but recent science has eroded the idea of a qualitative singularity in humans. We are merely quantitatively different.
Even single cells can be conditioned using the Pavlovian paradigm, which is a basic form of learning.
I'd expect an entity with complex and immutable information processing ability (no writable memory) to be purely sentient.
You're bang on the money with sapience being originally intended to be a merit badge for being human.
I'm guessing your last line was just riffing on functional purity but if not, my definition of sentience (which is a superset of consciousness) includes perception of current and past self-states which means (by my definitions, at least) an immutable construct isn't sentient by itself. I guess if you always pass in a self-state-vector then the system of (construct, self-state) could be conscious?
It's especially ironic because the very dogs in question were engineered by humans over vast generations, with a genetic engineering technique called selective breeding.
Dogs aren't just built, they're designed.