sim_scenario

Run a seeded what-if scenario against a stored model: marking overrides, rate overrides, piecewise rate schedules, and params assignments to the model's declared structural parameters (arc weights, capacities — batch sizes and shelf sizes). Pure read — asking cannot change the model. Returns trajectory, final marking, metrics, contention, caveats and assumptions. "samples" (default 60) is the trajectory's resolution: the number of evenly spaced points from 0 to hours inclusive at which times and every place's series (mean and std_dev per point) are reported — it sizes the answer, not the run, since metrics (throughput, mean, p95, utilization, inFlight) are time-weighted over every firing and do not change with the grid. "summary": true omits the times and series arrays entirely (the keys are absent, not null) and returns just final, metrics, depleted, contended, caveats and assumptions — the verdict without the chart data, and the right form when nothing will be plotted. Transitions declaring stages (phase-type durations) run with the declared lower spread — the engine expands them structurally and reports in the model's own vocabulary. A model-declared schedule (the day shape on a transition) is honored by every run; the scenario's own schedule or rate override still wins for that transition. "engine" picks the reading: "ssa" (default, discrete Gillespie — the right choice whenever counts are small enough that variance is the answer, or a schedule is in play) or "ode" (continuous mass-action; refuses a schedule, and refuses outright rather than silently misread a model carrying a read arc, inhibitor, reached capacity, guard or non-kinetic arc — Forecast's caveats name which). See docs/engine-selection.md for the full decision rule, including why an arc weight above 1 gets a genuinely different rate law from each engine, and sim_crosscheck to run both readings side by side.