PutPlayerInVehicle

// Global array to track which vehicle belongs to each player.
// INVALID_VEHICLE_ID is used as a placeholder for players without a vehicle.
static s_PlayerVehicle[MAX_PLAYERS] = { INVALID_VEHICLE_ID, ... };

public OnPlayerSpawn(playerid)
{
    // Check if the player already has a valid vehicle.
    if (!IsValidVehicle(s_PlayerVehicle[playerid]))
    {
        // If not, create a new vehicle for the player and store its ID.
        s_PlayerVehicle[playerid] = CreateVehicle(411, 0.0, 0.0, 3.5, 0.0, -1, -1, -1);
    }

    // Mark that the player should be placed in their vehicle once it is fully loaded.
    // This avoids issues where the vehicle might not yet be loaded on the client's side.
    SetPVarInt(playerid, "PutPlayerInVehicle", 1);

    return 1;
}

public OnVehicleStreamIn(vehicleid, forplayerid)
{
    // This callback is triggered when a vehicle streams in for the player (i.e. when it is loaded into memory).
    // Check if the streamed-in vehicle is the player's and if they need to be placed in it.
    if (vehicleid == s_PlayerVehicle[forplayerid] && GetPVarInt(forplayerid, "PutPlayerInVehicle"))
    {
        // Put the player into the vehicle.
        PutPlayerInVehicle(forplayerid, vehicleid, 0);

        // Clear the marker to prevent repeatedly putting the player into the vehicle
        // (e.g., if the player leaves the vehicle and it streams in again later).
        DeletePVar(forplayerid, "PutPlayerInVehicle");
    }

    return 1;
}