Demo350 — Graceful Degradation

public async Task<TriageResult> ClasserAsync(string request, ScenarioDemo scenario, CancellationToken cancellationToken)
{
    cancellationToken.ThrowIfCancellationRequested();
    if (scenario == ScenarioDemo.FallbackDirect)
        return fallback.Classer(request, "Explicit heuristic mode.");
    var pipeline = new ResiliencePipelineBuilder<TriageResult>().AddTimeout(
        scenario == ScenarioDemo.TimeoutSimule ? TimeSpan.FromSeconds(2) : timeout).Build();
    try
    {
        var result = await pipeline.ExecuteAsync(async token =>
        {
            if (scenario == ScenarioDemo.TimeoutSimule) await Task.Delay(Timeout.InfiniteTimeSpan, token);
            if (scenario == ScenarioDemo.OllamaIndisponibleSimule) throw new HttpRequestException("Simulated provider outage.");
            if (scenario == ScenarioDemo.SortieInvalideSimulee) throw new InvalidOperationException("Simulated invalid output.");
            var value = await model(request, token);
            if (value.Categorie is not ("Access" or "Billing" or "Incident" or "General")
                || string.IsNullOrWhiteSpace(value.Decision))
                throw new InvalidOperationException("Invalid triage output.");
            return value with { Origine = "Model", CauseBascule = null, Confiance = null,
                Explication = "Model classification; no calibrated confidence is available." };
        }, cancellationToken);
        cancellationToken.ThrowIfCancellationRequested();
        return result;
    }
    catch (OperationCanceledException) when (cancellationToken.IsCancellationRequested) { throw; }
    catch (Exception ex) when (ex is TimeoutRejectedException or OperationCanceledException
        or HttpRequestException or InvalidOperationException or System.Text.Json.JsonException)
    {
        cancellationToken.ThrowIfCancellationRequested();
        return fallback.Classer(request, ex.GetType().Name);