React to players and send messages

Use the session events, the player list, notices and messages. Side Hustle runs the Steam lobby, so you need no netcode of your own.

You need: a registered gamemode. See Add a gamemode.

Steps

Subscribe to the session events once, in the same class as your descriptor.
```
API.SessionStarted += ctx =>
{
    if (ctx.Descriptor.Id != "you.yourmode") return;   // fires for every gamemode
    Log.Msg($"started as {ctx.Role} with {API.Players.Count} player(s)");
};
API.SessionEnded += id => { if (id == "you.yourmode") Log.Msg("ended"); };
```
- SessionStarted fires after your launch callback returns. API.CurrentSession and API.Players are set by then.
- SessionEnded fires once, right after OnExitToHub. It also fires for a failed or aborted session.
- ctx.Role is Host, Client or Singleplayer.
Track players.
```
API.PlayerJoined += p => Log.Msg($"joined: {p}");
API.PlayerLeft += p => Log.Msg($"left: {p}");
```
- Players who are in the lobby at the start are in API.Players. They do not raise PlayerJoined.
- The list is polled about twice a second. In a World session, PlayerJoined fires before the character spawns.
- PlayerLeft does not fire for the remaining players when the session ends.
- SessionPlayer has SteamId, DisplayName, IsHost and IsLocal.
Show a notice to the local player.
```
API.ShowNotice("Round 2 starts in 10 seconds.", 5f);
```
In the world this is the game’s notification popup. In the menu it is the hub’s toast, with a fixed duration.
Send messages to the other players.
```
API.SendToAll("you.yourmode", "score", "red:3,blue:1");
API.SendTo(steamId, "you.yourmode", "role", "seeker");
```
- Messages go to the other players only, never to yourself.
- Delivery is reliable. A payload is at most API.MaxMessageBytes bytes.
- false means no session lobby or a refused message. The reason is in the log.
Receive messages.
```
API.OnMessage("you.yourmode", msg =>
{
    if (msg.Channel == "score") ApplyScore(msg.Text);
});
```
Handlers run on the main thread. Only members of the session lobby can send to you. SenderSteamId comes from Steam, not from the payload.
Optional, host only: remove a player.
```
API.KickPlayer(steamId, "Too many players");
```
It never kicks the host. On a client it does nothing.

All calls are safe from any thread. Calls off the main thread run on the next frame.

Check it works

Host your gamemode and join with a second instance.
The host log shows joined: with the client’s name.
Send a message from the client. The host’s handler runs with the client’s SenderSteamId.

Run on Side Hustle 2.x too

These members need Side Hustle 3.0. On an older Side Hustle they are missing, and a call fails. Ask for each feature by name before you use it:

if (SideHustleLink.Has("session-events") && SideHustleLink.Has("messages"))
    SideHustleLink.TryCall(() => Gamemode.Subscribe(), "lifecycle events", LoggerInstance);

The names are the constants on ApiFeatures, for example players, notices and messages.

React to players and send messages

Steps

Check it works

Run on Side Hustle 2.x too

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