Gaudi-XIX/dsbot-session-create

Adds four tools to a Session. create_session opens a new Session in a named workspace or in any existing folder and delivers one prompt into it; session_message adds one more message to a Session that is still running — the host is asked to splice it into that turn at once, instead of queueing it until the turn ends; a Session that has gone idle is refused, pointing back to create_session; read_session_transcript reads back what a Session said and whether its current turn has finished; list_dispatched_sessions lists what this plugin dispatched and each one's state right now. Host-half plugin, no UI — it calls the host's own session primitives rather than reimplementing them. Restart DSH after installing.