Phase 1a: focus spoofing + hook observability

Two problems surfaced in testing: (1) no way to tell whether the injected
hook was actually the input source, and (2) the final design needs the tool
window focused for Steam RPT capture, which would pause/silence games that
react to focus loss. Both are addressed here.

- Focus spoofing (hook/focus_spoof): find the game's main window, subclass it
  to rewrite/swallow WM_ACTIVATE/ACTIVATEAPP/NCACTIVATE/KILLFOCUS, and inline-
  hook GetForegroundWindow/GetActiveWindow/GetFocus to always report the game
  as active. The game keeps running and polling while unfocused.
- Status back-channel (protocol v2): the DLL reports attached/focus-spoof
  flags, game pid/hwnd, a heartbeat, and a cumulative XInputGetState counter.
  The host overlay turns the counter into a live poll rate, so "is the hook
  working" is directly observable.
- Synthetic test-input toggle in the host: forwards a known automated pattern
  (stick circle + periodic A) to prove forwarding independent of the physical
  pad.
- hook_selftest extended to assert the status channel; passes.

Documented the windowed/borderless requirement and the new observable test
flow in the README.

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

host/src/injection_panel.cpp

@@ -1,5 +1,7 @@
 #include "injection_panel.hpp"
 
+#include <cmath>
+
 #include <windows.h>
 
 #include "inject/injector.hpp"
@@ -108,6 +110,75 @@ void InjectionPanel::inject_selected()
 	}
 }
 
+void InjectionPanel::publish(const std::array<PadInfo, kMaxPads>& pads)
+{
+	if (!test_input_)
+	{
+		server_.publish(pads);
+		return;
+	}
+
+	// Synthetic, unmistakably non-human pattern: left stick sweeps a circle and
+	// A is pressed every other second. If the game moves on its own to this, the
+	// forwarding pipeline is proven end-to-end.
+	const unsigned long long ms = GetTickCount64();
+	const double t = static_cast<double>(ms) / 1000.0;
+
+	std::array<PadInfo, kMaxPads> synthetic{};
+	PadInfo& pad = synthetic[0];
+	pad.connected = true;
+	pad.source = "synthetic test";
+	pad.state.connected = 1;
+	pad.state.packet = static_cast<std::uint32_t>(ms);
+	pad.state.thumb_lx = static_cast<std::int16_t>(std::cos(t) * 30000.0);
+	pad.state.thumb_ly = static_cast<std::int16_t>(std::sin(t) * 30000.0);
+	if ((ms / 1000) % 2 == 0)
+	{
+		pad.state.buttons |= 0x1000; // XINPUT_GAMEPAD_A
+	}
+	server_.publish(synthetic);
+}
+
+void InjectionPanel::draw_hook_status()
+{
+	if (!server_.running())
+	{
+		return;
+	}
+
+	const HookStatusView status = server_.hook_status();
+
+	// Convert the cumulative query counter into a rate every half second.
+	const double now = ImGui::GetTime();
+	if (now - last_sample_time_ >= 0.5)
+	{
+		const double dt = now - last_sample_time_;
+		const unsigned long long delta =
+		    status.xinput_queries >= last_query_count_ ? status.xinput_queries - last_query_count_ : 0;
+		query_rate_ = dt > 0.0 ? static_cast<double>(delta) / dt : 0.0;
+		last_query_count_ = status.xinput_queries;
+		last_sample_time_ = now;
+	}
+
+	ImGui::SeparatorText("Hook status");
+	if (!status.attached)
+	{
+		ImGui::TextColored(kGrey, "Waiting for hook to attach in the game...");
+		return;
+	}
+
+	ImGui::TextColored(kGreen, "Attached (game pid %u, hwnd 0x%llX)", status.game_pid,
+	                   static_cast<unsigned long long>(status.game_hwnd));
+	ImGui::Text("XInput polled: %.0f/s (last slot %u)", query_rate_, status.last_user_index);
+	if (query_rate_ > 0.0)
+	{
+		ImGui::SameLine();
+		ImGui::TextColored(kGreen, " <- game is reading our input");
+	}
+	ImGui::TextColored(status.focus_spoof ? kGreen : kGrey, "Focus spoof: %s",
+	                   status.focus_spoof ? "active" : "inactive");
+}
+
 void InjectionPanel::draw()
 {
 	ImGui::SetNextWindowPos(ImVec2(24, 360), ImGuiCond_FirstUseEver);
@@ -168,6 +239,15 @@ void InjectionPanel::draw()
 		ImGui::TextColored(status_color_, "%s", status_.c_str());
 	}
 
+	ImGui::Checkbox("Forward synthetic test input", &test_input_);
+	if (test_input_)
+	{
+		ImGui::SameLine();
+		ImGui::TextDisabled("(ignores your controller)");
+	}
+
+	draw_hook_status();
+
 	ImGui::End();
 }