Broadcast engineering, from cable to code.

// HARD START: wait until exact start moment
var now = DateTime.Now;
if (current.StartType == MediaStartTimeTypes.Hard
    && now < current.StartTime)
    await Task.Delay(current.StartTime - now, hostCt)
        .ConfigureAwait(false);

var (offset, hardStopUtc) = ComputeTiming(current);

// FOLLOW end: preempt when next normal item has HARD start
DateTime? followPreemptLocal = null;
if (current.EndType == MediaEndTimeTypes.Follow)
    followPreemptLocal = PeekNextNormalHardStartTimeLocal();

// Run playback with its own CTS so we can preempt it
using var playCts =
    CancellationTokenSource.CreateLinkedTokenSource(hostCt);
var playTask = Task.Run(() => _engine.PlayAsync(
    current, offset, hardStopUtc, playCts.Token), playCts.Token);

public async Task RouteAsync(int output, int input, CancellationToken ct)
{
    await _out.WriteAsync($"VIDEO OUTPUT ROUTING:\n{output} {input}\n\n");

    List<string> reply;   // other clients' updates may arrive first
    do reply = await ReadBlockAsync(ct);
    while (reply is not (["ACK"] or ["NAK"]));

    if (reply is ["NAK"])
        throw new VideohubException($"Hub refused {input} -> {output}");
}

public async Task<(int Status, object Body)> HandleControlAsync(
    HttpRequest request)
{
    var config = _model.Settings.Web;
    if (!config.AllowControl)
        return Unpack(Fail(403, "HTTP control is switched off."));

    if (!Authorised(request, config.ApiKey))
        return Unpack(Fail(401, "Missing or wrong API key."));

    var args = request.Segments.Skip(1).Select(s => s.Trim()).ToList();

    // Same methods as the buttons, on the UI thread: a press from
    // Companion and a press on a tile can never disagree.
    var result = await _model.Dispatcher.InvokeAsync(
        () => Dispatch(args, request));
    return Unpack(result);
}

/// Writes are serialised through a semaphore so a preview frame
/// can never interleave with a control message.
private async Task WriteRawAsync(byte[] payload, CancellationToken ct)
{
    await _writeLock.WaitAsync(ct).ConfigureAwait(false);
    try
    {
        var prefix = new byte[4];
        BinaryPrimitives.WriteInt32BigEndian(prefix, payload.Length);
        await _stream.WriteAsync(prefix, ct).ConfigureAwait(false);
        await _stream.WriteAsync(payload, ct).ConfigureAwait(false);
        await _stream.FlushAsync(ct).ConfigureAwait(false);
    }
    finally
    {
        _writeLock.Release();
    }
}

const posts: WpPost[] = await res.json();

return posts
  .map((p): Slide => {
    const body = stripHtml(p.content.rendered);
    return {
      id: p.id,
      title: decodeEntities(p.title.rendered),
      body,
      seconds: clamp(body.length / cfg.cps, cfg.min, cfg.max),
      breaking: p.tags.includes(cfg.tagBreaking),
    };
  })
  // stable sort: breaking news first, otherwise newest first
  .sort((a, b) => Number(b.breaking) - Number(a.breaking));