Coming from CounterStrikeSharp

using CounterStrikeSharp.API;
using CounterStrikeSharp.API.Core;
using CounterStrikeSharp.API.Core.Attributes.Registration;
using CounterStrikeSharp.API.Modules.Commands;
using CounterStrikeSharp.API.Modules.Cvars;

public class KillHeal : BasePlugin
{
    public override string ModuleName => "Kill Heal";
    public override string ModuleVersion => "1.0.0";
    public override string ModuleAuthor => "You";
    public override string ModuleDescription => "Heals the killer";

    public FakeConVar<int> HealAmount = new("killheal_amount", "HP given per kill", 10);

    [GameEventHandler]
    public HookResult OnPlayerDeath(EventPlayerDeath @event, GameEventInfo info)
    {
        var attacker = @event.Attacker;
        if (attacker == null || !attacker.IsValid || attacker == @event.Userid || !attacker.PawnIsAlive)
            return HookResult.Continue;

        var pawn = attacker.PlayerPawn.Value;
        if (pawn == null)
            return HookResult.Continue;

        pawn.Health = Math.Min(pawn.Health + HealAmount.Value, 100);
        Utilities.SetStateChanged(pawn, "CBaseEntity", "m_iHealth");
        return HookResult.Continue;
    }

    [ConsoleCommand("css_hp", "Shows your health")]
    public void OnHp(CCSPlayerController? player, CommandInfo command)
    {
        var pawn = player?.PlayerPawn.Value;
        if (pawn != null)
            player!.PrintToChat($"You have {pawn.Health} HP.");
    }
}

#include "source2mod/ISource2ModPlugin.h"
#include "source2mod/ISource2ModApi.h"
#include "source2mod/schema/entity/classes/CCSPlayerController.h"
#include "source2mod/schema/entity/classes/CCSPlayerPawn.h"

#include "igameevents.h"

#include <algorithm>
#include <string>

SOURCE2MOD_GLOBALVARS();

// FakeConVar<int> -> a CConVar at file scope, registered in Load().
CConVar<int> killheal_amount("killheal_amount", FCVAR_NONE, "HP given per kill", 10);

class KillHeal final : public ISource2ModPlugin
{
public:
    bool Load(PluginId id, ISource2ModAPI* api, char* error, size_t maxlen, bool late) override
    {
        SOURCE2MOD_SAVEVARS();

        g_pCVar = api->GetCVar();
        ConVar_Register(FCVAR_RELEASE | FCVAR_CLIENT_CAN_EXECUTE | FCVAR_GAMEDLL);

        // [GameEventHandler] -> HOOK_GAME_EVENT, post = true.
        HOOK_GAME_EVENT("player_death", [](IGameEvent* event, bool post, bool& dontBroadcast) -> Action
        {
            auto* pVictim   = static_cast<CCSPlayerController*>(event->GetPlayerController("userid"));
            auto* pAttacker = static_cast<CCSPlayerController*>(event->GetPlayerController("attacker"));

            if (!pAttacker || pAttacker == pVictim || !pAttacker->m_bPawnIsAlive())
                return Action::Ignore;

            CCSPlayerPawn* pPawn = pAttacker->GetPlayerPawn();
            if (!pPawn)
                return Action::Ignore;

            // Assigning the field is what sends it to clients -- no SetStateChanged.
            pPawn->m_iHealth = std::min(pPawn->m_iHealth() + killheal_amount.Get(), 100);
            return Action::Ignore;
        }, true);

        // [ConsoleCommand("css_hp")] -> "hp", reachable as !hp and /hp.
        REGISTER_CON_COMMAND("hp", [](const Source2ModCommandContext& context, const Source2ModCommandArgs& args, bool post)
        {
            CCSPlayerController* pPlayer = CCSPlayerController::FromSlot(context.GetPlayerSlot());
            if (!pPlayer)
                return; // the server console

            CCSPlayerPawn* pPawn = pPlayer->GetPlayerPawn();
            if (!pPawn)
                return;

            const std::string message = "You have " + std::to_string(pPawn->m_iHealth()) + " HP.";
            pPlayer->PrintToChat(message.c_str());
        });

        return true;
    }

    bool Unload(char* error, size_t maxlen) override
    {
        // The event hook and the command are removed by Source2Mod.
        // ConVars are the one thing every plugin unregisters itself.
        ConVar_Unregister();
        return true;
    }

    const char* GetName() override { return "Kill Heal"; }
    const char* GetVersion() override { return "1.0.0"; }
    const char* GetAuthor() override { return "You"; }
    const char* GetDescription() override { return "Heals the killer"; }
};

KillHeal g_Plugin;
SOURCE2MOD_EXPOSE(killheal, g_Plugin);