Declares that one logical Baton.Flow.Step expands to one Baton node per item
in a collection drawn from the build subject.
gate controls scheduling within the expansion:
:parallel— every expanded node carries the step's declared deps, so they all run concurrently once those deps settle.:sequential— every expanded node carries the declared deps, and each is additionally sequenced after the previous one, chaining the expansion. Choose this when the expanded nodes share a cacheable prompt prefix (or you are smoothing a rate limit): the first call primes it and the rest read. Formerly named:warm_first, still accepted as a legacy alias.
The chaining edge orders, it does not depend: no data flows from one
expansion to the next, so a branch that fails permanently releases the gate
rather than cancelling everything behind it. Only the declared deps can fail
an expansion. See Baton.Check.