Metrics for a renderer connection (extension, not part of OGraf spec).
Added to RendererInfo response to provide observability without requiring
a separate metrics endpoint.
Not part of the OGraf spec itself (the spec has no instance state
machine) — this is Core’s own bookkeeping, inferred from which
action last succeeded, purely so dashboards/UIs can show more than
“a graphic is loaded here” (see store::renderers::apply_result).