Function drive_loop 

pub async fn drive_loop(
    ctx: &mut RunCtx,
    agent: &Agent,
    input: &Value,
) -> Result<LoopOutcome, RuntimeError>

Runs the built-in agent loop over an already-begun run, returning the final output (a LoopOutcome::Completed) or a park — but not recording the terminal RunCompleted.

The second half of [drive], made public so an external driver can run an agent loop inside a run it opened itself. The graph engine uses exactly this: it opens the log with GraphRunStarted, records NodeEntered, calls drive_loop (whose model and tool events land in the same log), records NodeExited, and moves to the next node — recording the single terminal RunCompleted only after its last node. Leaving the terminal to the caller is the whole reason the completion moved out of the loop and into [drive].

input is the already-begun run’s input (what [begin] returned).

Errors

Whatever the RunCtx operations surface: RuntimeError::Replay on divergence, RuntimeError::Model on a live provider failure, RuntimeError::Store on a persistence failure.