So: direct experimentation by animals is part of Skinnerian learning

Very few animals engage in anything that can be described as experimentation in any systematic fashion nor do they actually learn from the results in any fashion other than simple operant conditioning. Thus for example, if cats are placed in a box with a trick latch where they are given food after they get out, they gradually learn to hit the latch to the point where they can do so routinely. But, if one graphs the time it takes them on average to do so, they have a slow decline rather than a steep decline as one would expect if they were actually learning. If by experiment you mean "try lots of random things and not even understand which one actually helped" then yes they experiment. If one means experiment in a more useful fashion then very few species (great apes, corvids, keas, possibly elephants, possibly dolphins) do so.

Not one of the replies I expected - denying that animal trial-and-error learning is methodical enough to count as being "experimentation". That is probably true of some trial-and-error learning, but - as you seem to agree - some animal learning can be more methodical. I am still inclined to count experimentation as a "millions-of-years-old" phenomenon and part of conventional evolution - and not something to do with more recent developments involving engineering.

Imitating the strategies of others is hardly a new development either - animals have been imitating each other since around our LCA with songbirds - that too is an ordinary part of evolution.

This is a much more limited form of imitation, where evolution has simply given them an instinct to imitate sounds around them. In some cases this can be quite impressive (e.g. the lyrebird can imitate other birds, as well as camera clicks, car alarms and chainsaws) but they are essentially just imitating noises around them. The set of species that can look at another entity solve a problem and then learn from that to solve the problem is much tinier (humans, some other great apes, corvids, keas, African Grey Parrots dolphins, and not much else). There's a real difference in the type of imitation going on here.

I'd argue that even "local enhancement" - a very undemanding form of social learning - can result in incorporating the "solutions of other optimizing agents". Anyhow, again you seem to agree that animals have been doing such things for millions of years. So, this is still the domain of pretty conventional evolution.