TaskMonitorViewModel gains IsInteractiveLive + ComposerDraft + SubmitComposer
(optimistic LogKind.User echo, then SendInteractiveMessageAsync) + StopInteractive,
driven by the InteractiveSessionStarted/Ended events. Since DetailsIslandViewModel
embeds this monitor, both task detail and Mission Control get the composer. Mission
Control auto-creates a monitor on InteractiveSessionStarted. Adds LogKind.User.
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