Again, a product that facilitates the taking of notes, even notes that entail the killing of human beings, is fundamentally different from a product that exists to suggest which human beings to kill (or at least which places to destroy, regardless of whether human beings happen to be there or not).

If MS Word had some kind of systematic bias that made it likely to corrupt the notes taken in it such that they tend to be more bloody battle plans, then that would indeed lead to some responsibility on the MS engineer's part for any mistakes that result from this bug. Similarly for Ford engineers if their vehicles had some bug that made them more likely to lead soldiers riding in them to the wrong destination.

If your system is designed to help choose targets, and it chooses the wrong target, especially with such tragic consequences, then your system is likely not fit for purpose and you should be held responsible for selling it to the army. And that is assuming it didn't actually have some bias + misalignment problem where it intentionally tried to kill children, and selected this school specifically because it gave some plausible deniability. For all we know, it's even possible that some bias like this was known about inside Amthropic and hidden from the public - unless an external investigation is made, that can't be ruled out.

How intelligent and autonomous does a murderbot have to become before you stop absolving its creator and seller from any responsibility?

If the US military purchased camera guided smart munitions with a miscalibrated camera, such that it ignored adult targets and instead specifically targeted children, would that also be a simple mistake per your argument?