Function drive_draft 

pub async fn drive_draft(
    engine: &mut MissionEngine,
    repo: &Path,
    ticket: &Ticket,
    then_enqueue: bool,
) -> Result<DraftDrive>

Drive ticket through one non-interactive draft turn against an already-constructed engine (holding its backend): seed the orchestrator with the whole ticket, demand the plan, and resolve via draft_decision.

Backend-agnostic and side-effect-scoped to the ticket/queue filesystem state — no printing, no checkout restoration (the caller’s job). On a seed or plan-request error the ticket is rolled back to TicketState::New and the error is propagated.