Filters a dashboard section’s default widget layout. Each entry matches the dashboard’s widget instance shape: `uuid`, `type`, optional `attributes`, optional `placement`. Runs for every section, so a callback adding an instance to one switches on `$section_id`.
Parameters
- $layout
array The section's declared default widget instances.
- $section_id
string Namespaced section identifier, e.g. `analytics/traffic`.
- $section
Dashboard_Section The section.
