Answer posted by Dan Letecky [DayPilot] 1 years ago.
The missing TypeScript definitions have been added now in the latest sandbox build (2025.3.6529).
The only exception is DayPilot.GanttBeforeCellRenderArgs.cell.areas - this is already available but it needs to be accessed as DayPilot.GanttBeforeCellRenderArgs.cell.properties.areas.
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