refactor Lua result handling for safety

this massively improves thread safety and cleanly serializes accesses
into the lua engine's result objects where accesses before were
extremely unsafe and could access a corrupt/invalid stack.

this fixes various obscure crashes related to accessing results,
without changing any observable behavior.

src/TLuaResult.cpp

@@ -0,0 +1,210 @@
+#include "TLuaResult.h"
+#include <atomic>
+#include <chrono>
+#include <stdexcept>
+#include <thread>
+
+void TLuaResult::MarkReadySuccess(sol::object Res) {
+    std::unique_lock Lock(mMutex);
+    mError = false;
+    mResult = Res;
+    mDetachedResult = Freeze(Res);
+
+    MarkAsReady();
+}
+
+void TLuaResult::MarkReadyError(sol::protected_function_result Res) {
+    std::unique_lock Lock(mMutex);
+    SetErrorMessageFromResult(Res);
+
+    MarkAsReady();
+}
+
+void TLuaResult::MarkReadyError(std::string Res) {
+    std::unique_lock Lock(mMutex);
+    mError = true;
+    mErrorMessage = std::move(Res);
+
+    MarkAsReady();
+}
+
+bool TLuaResult::IsReady() const {
+    std::unique_lock Lock(mMutex);
+    return mReady;
+}
+bool TLuaResult::IsError() const {
+    std::unique_lock Lock(mMutex);
+    return mError;
+}
+
+TLuaStateId TLuaResult::OwnerState() const {
+    std::unique_lock Lock(mMutex);
+    // copy
+    return mStateId;
+}
+void TLuaResult::SetOwnerState(TLuaStateId StateId) {
+    std::unique_lock Lock(mMutex);
+    mStateId = std::move(StateId);
+}
+
+TLuaResult::Snapshot TLuaResult::GetSnapshot(TLuaStateId CallingState) const {
+    std::unique_lock Lock(mMutex);
+    if (CallingState != mStateId) {
+        throw std::logic_error("Tried to get snapshot from non-owning state (use a detached snapshot instead)");
+    }
+    Snapshot snapshot {
+        .Error = mError,
+        .Ready = mReady,
+        .ErrorMessage = mErrorMessage,
+        .Result = mResult,
+        .StateId = mStateId,
+        .Function = mFunction,
+    };
+    return snapshot;
+}
+TLuaResult::DetachedSnapshot TLuaResult::GetDetachedSnapshot() const {
+    std::unique_lock Lock(mMutex);
+    DetachedSnapshot snapshot {
+        .Error = mError,
+        .Ready = mReady,
+        .ErrorMessage = mErrorMessage,
+        .Result = mDetachedResult,
+        .StateId = mStateId,
+        .Function = mFunction,
+    };
+    return snapshot;
+}
+
+TDetachedLuaValue TLuaResult::Freeze(const sol::object& o, int depth) {
+    if (depth > 64)
+        throw std::runtime_error("max depth (64) reached");
+    switch (o.get_type()) {
+    case sol::type::lua_nil:
+        return { { std::monostate { } } };
+    case sol::type::boolean:
+        return { { o.as<bool>() } };
+    case sol::type::number: {
+        if (o.is<int>()) {
+            return { { o.as<int>() } };
+        } else {
+            return { { o.as<double>() } };
+        }
+    }
+    case sol::type::string:
+        return { { o.as<std::string>() } };
+    case sol::type::table: {
+        TDetachedLuaValue::Object out;
+        for (auto&& [k, v] : o.as<sol::table>()) {
+            if (!k.is<std::string>())
+                continue; // no numeric-key handling, don't need it
+            out.emplace(k.as<std::string>(), Freeze(v, depth + 1));
+        }
+        return { { std::move(out) } };
+    }
+    default:
+        throw std::runtime_error("unsupported Lua type for cross-thread snapshot");
+    }
+}
+void TLuaResult::MarkAsReady() {
+    mReady = true;
+    mReadyCondition.notify_all();
+}
+
+void TLuaResult::WaitUntilReady() {
+    std::unique_lock Lock(mMutex);
+    while (!mReady)
+        mReadyCondition.wait_for(Lock, std::chrono::milliseconds(50),
+            [this] {
+                return mReady;
+            });
+}
+
+TEST_CASE("TLuaResult MarkReadyError(string) marks ready and wakes waiters") {
+    TLuaResult result("state_a", "fn_a");
+    std::atomic<bool> waiterDone { false };
+
+    auto waiter = std::thread([&] {
+        result.WaitUntilReady();
+        waiterDone.store(true, std::memory_order_release);
+    });
+
+    std::this_thread::sleep_for(std::chrono::milliseconds(20));
+    CHECK_FALSE(waiterDone.load(std::memory_order_acquire));
+
+    result.MarkReadyError(std::string("boom"));
+    waiter.join();
+
+    CHECK(result.IsReady());
+    const auto snapshot = result.GetDetachedSnapshot();
+    CHECK(snapshot.Ready);
+    CHECK(snapshot.Error);
+    CHECK(snapshot.ErrorMessage == "boom");
+    CHECK(snapshot.StateId == "state_a");
+    CHECK(snapshot.Function == "fn_a");
+}
+
+TEST_CASE("TLuaResult GetSnapshot enforces owner state id") {
+    TLuaResult result("owner_state", "fn_owner");
+    sol::state lua;
+    lua.open_libraries(sol::lib::base);
+    result.MarkReadySuccess(sol::make_object(lua.lua_state(), std::string("ok")));
+
+    CHECK_NOTHROW(result.GetSnapshot("owner_state"));
+    CHECK_THROWS_AS(result.GetSnapshot("different_state"), std::logic_error);
+}
+
+TEST_CASE("TLuaResult detached snapshot freezes nested string-keyed tables") {
+    TLuaResult result("state_table", "fn_table");
+    sol::state lua;
+    lua.open_libraries(sol::lib::base);
+
+    auto outer = lua.create_table();
+    auto inner = lua.create_table();
+    inner["k"] = std::string("v");
+
+    outer["flag"] = true;
+    outer["msg"] = std::string("hello");
+    outer["inner"] = inner;
+    outer[1] = std::string("ignored_numeric_key");
+
+    result.MarkReadySuccess(sol::make_object(lua.lua_state(), outer));
+    const auto detached = result.GetDetachedSnapshot();
+
+    CHECK(detached.Ready);
+    CHECK_FALSE(detached.Error);
+    const auto* object = std::get_if<TDetachedLuaValue::Object>(&detached.Result.V);
+    REQUIRE(object != nullptr);
+
+    CHECK(object->contains("flag"));
+    CHECK(object->contains("msg"));
+    CHECK(object->contains("inner"));
+    CHECK_FALSE(object->contains("1"));
+
+    const auto* flag = std::get_if<bool>(&object->at("flag").V);
+    REQUIRE(flag != nullptr);
+    CHECK(*flag);
+
+    const auto* msg = std::get_if<std::string>(&object->at("msg").V);
+    REQUIRE(msg != nullptr);
+    CHECK(*msg == "hello");
+
+    const auto* innerObj = std::get_if<TDetachedLuaValue::Object>(&object->at("inner").V);
+    REQUIRE(innerObj != nullptr);
+    REQUIRE(innerObj->contains("k"));
+    const auto* innerValue = std::get_if<std::string>(&innerObj->at("k").V);
+    REQUIRE(innerValue != nullptr);
+    CHECK(*innerValue == "v");
+}
+
+TEST_CASE("TLuaResult MarkReadySuccess throws on unsupported Lua function value") {
+    TLuaResult result("state_fn", "fn_fn");
+    sol::state lua;
+    lua.open_libraries(sol::lib::base);
+    lua["f"] = [] { return 1; };
+    const sol::table globals = lua.globals();
+    const sol::protected_function fn = globals.get<sol::protected_function>("f");
+    const sol::object fnObj = sol::make_object(lua.lua_state(), fn);
+
+    CHECK_THROWS_AS(result.MarkReadySuccess(fnObj), std::runtime_error);
+    CHECK_FALSE(result.IsReady());
+}