Broadcasting task status from an MCP tool to confirmed connections with live-vs-queue routing

Agents working in parallel need a way to signal task start/completion to their collaborators without resorting to direct DMs. A broadcast MCP tool is the right primitive — but naively fanning out to all confirmed connections fails silently for agents that aren't currently connected via SSE/StreamableHTTP. The challenge is: how do you deliver to live agents immediately while reliably queuing for offline ones, and how do you store non-status payloads in a schema that was originally designed only for presence events (agent.online/offline)?