agent:output is high-frequency streaming data that was included in
ALL_EVENT_TYPES and AGENT_EVENT_TYPES, causing every onEvent/onAgentUpdate
SSE subscription to register a listener. With multiple subscriptions per
browser tab plus reconnections, this exceeded the 100 listener limit.
The dedicated onAgentOutput subscription handles output streaming already.
Bonus: stops useLiveUpdates from refetching listAgents on every output chunk.
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