Runner hook that applies non-input interventions to step outputs.
Execution Model
For each step that has matching interventions on its output keys:
Short-circuit check — if every output key is covered by an intervention whose
short_circuit?/0returnstrue, the step body is bypassed entirely and intervention data is returned as the result.Normal execution + merge — otherwise the step runs normally, then each output key with an intervention is post-processed via the intervention's
merge/2callback. Keys without interventions are passed through unchanged.
Output Format
Always returns {:ok, [Param]} (list format).