But that dependency order is usually just one big blob of ”COPY src/ . + RUN make”, within that block you have none of the benefits. Bazel/Buck has much finer awareness down to every individual file.

Out of curiosity, would it be feasible to take a big cmake project and generate thousands of compile rules into dagger and use it as a substitute for make with sandboxing? I’ve never seen builkit used with such many nodes, how would it fare?

Yes, but that does not help you build declaratively in dagger, does it? I would like to see an example of how to do so, if you have one.