Agents in `active` state without a current taskId had no SSE to attach
to, but the card still rendered "Connecting..." — implying a network
state that never resolves. Branch on taskId first: idle agents show
"Idle — no task assigned"; running-without-task shows "Starting...".
Also fix a related SSE multiplexer race: subscribers joining a channel
that had already opened never got an onOpen callback (EventSource only
fires `open` once), so they sat at isConnected=false forever whenever
another component was already streaming the same URL. Fire onOpen on a
microtask for late-joiners.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
