Define the outcome before collecting the metric
An execution is a technical event. An outcome is the useful result the business accepts. For an invoice workflow, the outcome might be a reviewed record ready for the next authorized step. For a reporting workflow, it might be a report accepted by its owner with no unresolved required fields.
Write the acceptance rule in operational language. Identify who decides, what evidence they inspect, and which defects require rework. Without that rule, the team can improve its success rate simply by changing what “success” means.
Track separate states for completed processing, accepted output, rejected output, and unresolved cases. A timeout should not disappear from the denominator because it never reached the final node. A rejected draft should not count as an accepted outcome because the model returned valid JSON.
I would keep the acceptance rule versioned. If the business changes its standard during a pilot, the report should identify which cases were judged under each version.