Resolve a substitutive level's role from its parent group's live state.
Unknown (no state yet) → undefined, so rows aren't mis-marked before
the first provider poll. Shared by the initial render and the monitor's
incremental level-row patcher so both derive the role identically.
Resolve a substitutive level's role from its parent group's live state. Unknown (no state yet) →
undefined, so rows aren't mis-marked before the first provider poll. Shared by the initial render and the monitor's incremental level-row patcher so both derive the role identically.