Notes

• Parameter mapping. Each key in parameterMap is a parameter name on the child sub-report. Each value is either a literal ("USA") or an expression (=Variables.selectedOrder.id) evaluated in the parent context before being passed in.
• Drill writes the whole row. A TableComponentProps.onDrillThrough writes the entire clicked row into the variable. Use Variables.foo.field in downstream expressions to extract what you need — or use a cell-item drill action with drillValueExpr to write a specific value.
• Sub-report discovery. The parent builder's sub-report picker reads availableSubReports — the schema (id, label, parameter list). The viewer gets subReportDefinitions — the full definitions needed to render. On this page, both are derived from the same shared store.
• Gating a sub-report on state. The parent's Order Details sub-report is hidden via styles.visible: "=!IsEmpty(Variables.selectedOrder)" so it only appears once a row has been drilled.
• Own datasources. Each sub-report declares its own datasources and fetches them independently — there is no shared pool. If both parent and child need the same dataset, declare it on both.