Storybook Manager UI and React preview iframe args merge semantics

Goal is to define predictable interoperability between Storybook CSF 3 story definitions and React component rendering when args, defaultProps and control overrides intersect.

The integration boundary is between the Manager UI that stores and edits args and the preview iframe that renders the component. Merge strategy for nested objects, functions and refs is implementation defined and varies by framework preset. Autodocs inference and display name resolution are not standardized across presets. Storybook UI provides no built-in pagination for the stories list, so large collections rely on search, grouping and sidebar virtualization with unspecified performance trade-offs.

What merge order is applied for nested object props between defaultProps, story args and control overrides? Is deep merge behavior stable across Storybook major versions and React preset releases? How does args state synchronization between Manager UI and preview iframe behave under async updates in large story sets?