Hand the lead of a one-to-one LinkedIn thread over to a teammate. LinkedIn adds nobody to a one-to-one, so the thread's sender profile opens a LinkedIn group with the lead and the teammate, and message is its first message. Name the teammate: to_sender_profile_sid for a sender profile here (the task goes to its user), to_target for anyone else (a link, slug or URN).

It leaves behind result.group (the new thread), result.message (the queued introduction; a failed one is sent again with retry_messages) and result.task (who goes on). The one-to-one thread (item) is closed; both get a handed_over pill naming the other; the AI SDR is off on every live thread of the lead (plans superseded, runs, drafts and queued sends canceled). A message in result.group goes out as the handing sender profile. Hand back: reopen the thread and clear agent_mode_override (update_conversation).

Refusals write nothing: 409 already_a_group (add_conversation_participants instead), stoplisted, no_linkedin_channel, lead_not_on_linkedin, lead_unresolvable, already_handed_over (context.group_conversation_sid), sender_profile_unknown, sender_unavailable; 422 on the field that named the teammate (teammate_is_lead, teammate_is_sender, teammate_has_no_linkedin, teammate_unresolvable, not_a_linkedin_profile, profile_unresolvable) or gtm_connection_not_active; 403 account_not_allowed, gtm_scope_missing; 429 gtm_busy or bucket_saturated, 503 gtm_unavailable or playtables_unavailable: try later.

Contract:

• MCP tool hand_over_conversation, registry package mcp.unibox/conversations, mount unibox.inbox.
• Operation action, response envelope action.
• Flags: dangerous: the MCP layer gates it behind a preview/commit token, and the effect cannot be undone through this API.