A financial services company has implemented Google Analytics 4 across its main marketing website and a separate, secure client portal hosted on a different domain. The marketing team observes that when a user clicks 'Login' on the marketing site, their session ends, and a new session begins on the client portal, inflating user counts and breaking the user journey analysis. The primary goal is to see the entire user path from initial ad click to a specific action within the client portal as a single, continuous journey. The current setup uses the same GA4 measurement ID on both domains. The marketing team has confirmed the tracking code is firing correctly on all pages. However, referral reports show the main marketing domain as a top traffic source to the client portal, confirming the session break. The company's compliance department requires that no personally identifiable information (PII) is captured in GA4. Which configuration change should the analytics consultant recommend to resolve the session fragmentation issue while respecting all constraints?