Function run_lesson 

pub async fn run_lesson(
    lesson: &Lesson,
    submission: &Submission,
    provider: ProviderChoice,
    base_url_override: Option<&str>,
) -> Result<RunReport, RunError>

Run submission against lesson and produce a RunReport.

The orchestrator (§2.4): it selects the lesson’s runner, executes the submission on its own to capture the output the report carries and the prompt shows, grades the lesson’s checks, builds the feedback prompt, and asks provider for a verdict — composing each layer through its public type and adding no domain logic of its own. base_url_override points the provider at a stub in tests (the request_feedback seam) and is None in production. Short and linear: the only branch is error propagation.

The output-capturing run is separate from grading: when the lesson has checks, run_checks runs the submission again as its own gate (see grade), so a submission with side-effecting or nondeterministic output could in principle diverge between the captured output and what the checks graded against. This is benign under v0’s trusted-local, deterministic-submission model, and the common LLM-only lesson has no checks — so the submission runs exactly once. Folding the gate’s output back into grading (to run once even with checks) is a grade-layer change left to a later slice.