Phase 1a: input forwarding via DLL injection + XInput hook

The host can now inject coop_hook.dll into a running game and forward
controller state to it over shared memory, so the game reads the host's
(eventually the guest's) input and nothing else.

- hook/: coop_hook.dll. DllMain spawns a worker that opens the shared-memory
  channel (named by the game's pid) and installs SafetyHook inline hooks on
  XInputGetState/GetStateEx/GetCapabilities/SetState. Detours synthesize state
  from shared memory; unmanaged slots report disconnected, hiding physical pads.
- host/: process picker (Toolhelp32), CreateRemoteThread(LoadLibraryW) injector
  with an IsWow64Process2 bitness guard, IPC server publishing pads each frame,
  and an ImGui Injection panel wiring it together.
- tests/: hook_selftest exercises the IPC seqlock + hook detours in-process
  (no game/controller needed); passes.

Build: SafetyHook wired in (COOP_BUILD_HOOK=ON), Zydis via FetchContent.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

hook/src/xinput_hook.cpp

@@ -0,0 +1,192 @@
+#include "xinput_hook.hpp"
+
+#include <array>
+#include <atomic>
+#include <vector>
+
+#include <windows.h>
+#include <xinput.h>
+
+#include <safetyhook.hpp>
+
+namespace coop::hook
+{
+
+namespace
+{
+
+// XInput guide-button bit, reported only by the undocumented ordinal-100
+// XInputGetStateEx that many games use. Mirrors how Steam/x360ce expose it.
+constexpr std::uint16_t kGuideButton = 0x0400;
+
+const IpcClient* g_ipc = nullptr;
+std::vector<safetyhook::InlineHook> g_hooks;
+
+// Last good snapshot, so a momentary failed IPC read (host mid-write) doesn't
+// flicker the controller as disconnected inside the game.
+std::array<CoopPadState, kMaxPads> g_cache;
+
+void refresh_cache()
+{
+	if (g_ipc == nullptr)
+	{
+		return;
+	}
+	CoopPadState pads[kMaxPads];
+	std::uint32_t count = 0;
+	if (g_ipc->snapshot(pads, count))
+	{
+		for (std::uint32_t i = 0; i < kMaxPads; ++i)
+		{
+			g_cache[i] = pads[i];
+		}
+	}
+}
+
+void fill_gamepad(const CoopPadState& pad, XINPUT_GAMEPAD& out)
+{
+	out.wButtons = pad.buttons;
+	out.bLeftTrigger = pad.left_trigger;
+	out.bRightTrigger = pad.right_trigger;
+	out.sThumbLX = pad.thumb_lx;
+	out.sThumbLY = pad.thumb_ly;
+	out.sThumbRX = pad.thumb_rx;
+	out.sThumbRY = pad.thumb_ry;
+}
+
+// Core of every state query. `keep_guide` drops the guide bit for the plain
+// (documented) XInputGetState, which must not report it.
+DWORD query_state(DWORD user_index, XINPUT_STATE* state, bool keep_guide)
+{
+	if (state == nullptr || user_index >= kMaxPads)
+	{
+		return ERROR_DEVICE_NOT_CONNECTED;
+	}
+	refresh_cache();
+	const CoopPadState& pad = g_cache[user_index];
+	if (!pad.connected)
+	{
+		return ERROR_DEVICE_NOT_CONNECTED;
+	}
+
+	XINPUT_STATE result = {};
+	result.dwPacketNumber = pad.packet;
+	fill_gamepad(pad, result.Gamepad);
+	if (!keep_guide)
+	{
+		result.Gamepad.wButtons &= ~kGuideButton;
+	}
+	*state = result;
+	return ERROR_SUCCESS;
+}
+
+DWORD WINAPI hk_XInputGetState(DWORD user_index, XINPUT_STATE* state)
+{
+	return query_state(user_index, state, /*keep_guide=*/false);
+}
+
+DWORD WINAPI hk_XInputGetStateEx(DWORD user_index, XINPUT_STATE* state)
+{
+	return query_state(user_index, state, /*keep_guide=*/true);
+}
+
+DWORD WINAPI hk_XInputGetCapabilities(DWORD user_index, DWORD /*flags*/, XINPUT_CAPABILITIES* caps)
+{
+	if (caps == nullptr || user_index >= kMaxPads)
+	{
+		return ERROR_DEVICE_NOT_CONNECTED;
+	}
+	refresh_cache();
+	if (!g_cache[user_index].connected)
+	{
+		return ERROR_DEVICE_NOT_CONNECTED;
+	}
+
+	// Advertise a standard wired Xbox-style gamepad with all controls present.
+	XINPUT_CAPABILITIES result = {};
+	result.Type = XINPUT_DEVTYPE_GAMEPAD;
+	result.SubType = XINPUT_DEVSUBTYPE_GAMEPAD;
+	result.Flags = 0;
+	result.Gamepad.wButtons = 0xF3FF; // all standard buttons reachable
+	result.Gamepad.bLeftTrigger = 0xFF;
+	result.Gamepad.bRightTrigger = 0xFF;
+	result.Gamepad.sThumbLX = static_cast<SHORT>(0x7FFF);
+	result.Gamepad.sThumbLY = static_cast<SHORT>(0x7FFF);
+	result.Gamepad.sThumbRX = static_cast<SHORT>(0x7FFF);
+	result.Gamepad.sThumbRY = static_cast<SHORT>(0x7FFF);
+	*caps = result;
+	return ERROR_SUCCESS;
+}
+
+// Swallow rumble: it would otherwise be sent to whatever physical device sits at
+// this index on the host machine. Forwarding it back to the guest is a later
+// phase; for now report success so the game's logic is happy.
+DWORD WINAPI hk_XInputSetState(DWORD user_index, XINPUT_VIBRATION* /*vibration*/)
+{
+	if (user_index >= kMaxPads || !g_cache[user_index].connected)
+	{
+		return ERROR_DEVICE_NOT_CONNECTED;
+	}
+	return ERROR_SUCCESS;
+}
+
+void hook_export(HMODULE module, const char* name, void* detour)
+{
+	if (module == nullptr)
+	{
+		return;
+	}
+	if (void* target = reinterpret_cast<void*>(GetProcAddress(module, name)))
+	{
+		g_hooks.emplace_back(safetyhook::create_inline(target, detour));
+	}
+}
+
+void hook_ordinal(HMODULE module, WORD ordinal, void* detour)
+{
+	if (module == nullptr)
+	{
+		return;
+	}
+	if (void* target = reinterpret_cast<void*>(GetProcAddress(module, MAKEINTRESOURCEA(ordinal))))
+	{
+		g_hooks.emplace_back(safetyhook::create_inline(target, detour));
+	}
+}
+
+} // namespace
+
+bool install_xinput_hooks(const IpcClient& ipc)
+{
+	if (!g_hooks.empty())
+	{
+		return true; // already installed
+	}
+	g_ipc = &ipc;
+	refresh_cache();
+
+	// A process generally loads exactly one of these, but hook every one that is
+	// present so we don't miss the one the game actually calls.
+	const wchar_t* modules[] = {L"xinput1_4.dll", L"xinput1_3.dll", L"xinput9_1_0.dll", L"xinputuap.dll"};
+	for (const wchar_t* name : modules)
+	{
+		HMODULE module = GetModuleHandleW(name);
+		if (module == nullptr)
+		{
+			continue;
+		}
+		hook_export(module, "XInputGetState", reinterpret_cast<void*>(&hk_XInputGetState));
+		hook_ordinal(module, 100, reinterpret_cast<void*>(&hk_XInputGetStateEx));
+		hook_export(module, "XInputGetCapabilities", reinterpret_cast<void*>(&hk_XInputGetCapabilities));
+		hook_export(module, "XInputSetState", reinterpret_cast<void*>(&hk_XInputSetState));
+	}
+	return !g_hooks.empty();
+}
+
+void remove_xinput_hooks()
+{
+	g_hooks.clear(); // InlineHook destructor restores the original bytes
+	g_ipc = nullptr;
+}
+
+} // namespace coop::hook