PMP Practice: Break down situation to identify the root cause of a misunderstanding

River Tanaka is managing a pharmaceutical compliance system upgrade at Swift Horizon Labs. During a requirements review meeting, the quality assurance lead insists that 'full validation' means testing every possible user path, while the IT director states that 'full validation' only requires testing critical business processes. Both are referencing the approved project charter, which states the system must undergo 'full validation' before go-live. The two stakeholders are now debating what this means, and the meeting has stalled. River has not previously clarified this terminology with either stakeholder. What should River do?