How to fetch system data inside a solution extension (property editor dropdown / runtime)

[talwind]

I'm building a toolbar solution extension and need to fetch data from the VI system in two scenarios:

1. In Page Builder (property editor): I want to show the admin a dropdown list populated from the system (e.g. list of workflow definitions) instead of a free-text input.
2. At runtime (on the page): I want to display data from the system inside the control itself (e.g. reference data hierarchy).

What is the recommended approach? Should I use the VI REST APIs directly via fetch? Is there a built-in mechanism through controlApi or window.sas.vi?

Specifically for scenario 1 — when using registerCustomEditor, how does the custom element write the selected value back to the control's typeAttributes?

Sonnet 4.6

Adaptive