Function accumulateAllowedAgents

UNION-accumulates realtime.allowedAgents across cascade layers (base first) plus optional dynamic additions. Deduped by agentId (case/whitespace-insensitive); later sources win per field (a later layer that only sets disclosure keeps an earlier layer's label).

This is the deliberate exception to the array-replace merge rule — the lead co-agent should accumulate colleagues as layers add them, not have the top layer clobber the set.