I don't see how buildkit could possibly build the correct dependency tree because the Dockerfile language doesn't let you express nonlinear dependencies.

If you have a command `do_foo` that depends on do_bar and do_baz (but do_bar and do_baz are independent) and you do something like:

    RUN do_bar # line 1
    RUN do_baz # line 2
    RUN do_foo # line 3

I'm guessing the buildkit dep graph will look like `line_3 -> line_2 -> line_1` (linear). Unless there is some new way of expressing to Docker that do_foo depends on do_bar and do_baz but that the latter two are independent.

EDIT: clarified example.