GTM API / Mass-action metrics

Where a run is right now, in one round-trip, without paging items. Typical call: filter {sid:{eq}}. Returns items_by_status (the outcome split), items_by_current_step, items_by_wait_reason, in_flight (0 means the run is caught up), the next / last scheduled item, created_objects and the top error prefixes. No group_by: the shape is fixed. Use this instead of listing a run's items to answer 'how is it going'. Contract: - MCP tool get_mass_actions_metrics, registry package mcp.orchestration/mass_actions, mount orchestration.mass_actions. - Operation metrics, response envelope metrics. - Flags: read only.