PR: Issue with IfcSystem export when using 'Export only elements visible in view'

### Problem Description

Dear IFC Exporter Development Team,

We have identified an issue in Revit 2024/2025/2026 (IFC Exporter 2024.3.x) related to the option:

“Export only elements visible in view”.

When this option is enabled, Electrical Circuits (exported as IfcDistributionSystem / IfcDistributionCircuit in IFC4 and IfcElectricalCircuit in IFC2x3) are not written to the IFC file, even though:
- The circuits exist in the Revit model
- The circuits contain valid elements
- The elements themselves are exported

Observed behavior:
If the export is limited to visible elements, the exporter does not write the corresponding IfcSystem / IfcDistributionCircuit objects and their IfcRelAssignsToGroup relationships. As a result, system relationships are lost in the IFC.

When the visibility restriction is disabled (full model export), the systems and their relationships are correctly written.

Impact:
This breaks the integrity of system relationships in coordination workflows. In downstream tools (e.g. Solibri), the elements no longer show “Assigned to Group” relationships, even though they are part of a circuit in Revit.

Requested improvement:
We would like the exporter to preserve IfcSystem / IfcDistributionCircuit objects and their IfcRelAssignsToGroup relationships for all exported elements, even when “Export only elements visible in view” is enabled.
If an element is exported, its system relationship should remain intact.

In other words:
Visibility filtering should not break relational integrity of systems.

Please let us know if this behavior is intentional or if it can be addressed in a future exporter update.

Kind regards,
Dennis Ruck
BIM Maximaal

### Revit Version

2024.3.x

### IFC for Revit Addon Version

24.3.40

### Windows Version

11 25H2

Start by reproducing the Revit 2024.3.x export with “Export only elements visible in view” enabled and compare it with a full-model IFC export. Trace the visibility filtering and the creation of IfcSystem/IfcDistributionCircuit objects and IfcRelAssignsToGroup relationships; done means exported circuit elements retain those systems and relationships.

Written by the indexing model from the issue text.