Report Controller

Each report has a ReportController.

Member	Purpose
id	Stable report id.
kind	Report kind.
config	Normalized report config.
state	Current report state.
descriptor	Renderer descriptor or null.
subscribe(listener)	Listen to report state changes.

ReportStateSnapshot contains:

Field	Meaning
payload	Raw payload selected for the report.
error	Report-local error message, if resolution failed.
status	idle, ready, or error.

Use source on report config when a backend key differs from the report id.