Detect terminated / hung target and reflect it in the UI

The Injection panel kept showing "Attached" after the game exited. Now it tracks
target liveness each frame (InjectionPanel::tick from the main loop, independent of
panel visibility):
- a SYNCHRONIZE|QUERY process handle taken at inject time -> WaitForSingleObject
  detects the process exiting (Terminated);
- the hook heartbeat stalling for ~2 s while the process still exists flags a
  distinct Hung state (games here can freeze without exiting).

The panel shows a clear colored banner per state and disables the subsystem
hook/unhook controls and the synthetic-input toggle when the target isn't alive.
game_hwnd() returns null once Terminated, so the Video and Audio panels drop to
idle instead of chasing a dead window.

Verified: x64 build + ctest 7/7 green; host launches and renders the panels without
regression (screenshot smoke test). The interactive terminated/hung visual against a
real game is best confirmed in a live session (ImGui injection can't be GUI-scripted).

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

README.md

@@ -75,18 +75,6 @@ is removed from this list once done — so the top item is always next. The
 self-verifiable tooling / UI / input items come first; the game-pipeline items that
 need a real game (and Remote Play) to fully validate come last.
 
-- **Detect a terminated target and reflect it in the UI.** The Injection panel keeps
-  showing "Attached" after the game exits. Add a **Terminated** state: the host
-  already knows the target pid and tracks a DLL heartbeat (`InjectionPanel`); on top
-  of that, hold the `OpenProcess` handle from injection (or re-open with
-  `PROCESS_QUERY_LIMITED_INFORMATION`) and poll `GetExitCodeProcess` /
-  `WaitForSingleObject(h, 0)` each tick. When the process is gone, switch to
-  Terminated, gray out / disable the per-subsystem controls and mirror toggles, and
-  show a clear banner; the Video and Audio panels should drop to idle (their hook
-  channels are stale) rather than freezing on the last live frame/state. Note a live
-  process isn't proof it's running — also flag a **stalled heartbeat** (no advance
-  for ~2 s while the process still exists) as a distinct "hung / not responding"
-  state, since games here can freeze without exiting.
 - **Re-attach to a relaunched target.** A killed-and-relaunched game gets a new pid,
   but the UI still holds the stale one. In the Terminated state, remember the
   target's image name (the panel already keeps the selected exe name) and offer a

host/src/injection_panel.cpp

@@ -69,6 +69,64 @@ InjectionPanel::InjectionPanel()
 	refresh_processes();
 }
 
+InjectionPanel::~InjectionPanel()
+{
+	close_target_handle();
+}
+
+void InjectionPanel::close_target_handle()
+{
+	if (target_process_ != nullptr)
+	{
+		CloseHandle(target_process_);
+		target_process_ = nullptr;
+	}
+	target_state_ = TargetState::NotInjected;
+	dll_alive_ = false;
+	last_heartbeat_ = 0;
+	last_heartbeat_time_ = 0.0;
+}
+
+void InjectionPanel::tick()
+{
+	update_liveness();
+}
+
+void InjectionPanel::update_liveness()
+{
+	if (!injected_)
+	{
+		target_state_ = TargetState::NotInjected;
+		return;
+	}
+
+	// Process gone? The handle was opened with SYNCHRONIZE at inject time, so a
+	// signaled wait means it exited. This is authoritative even if the heartbeat
+	// happened to look alive a moment ago.
+	if (target_process_ != nullptr && WaitForSingleObject(target_process_, 0) == WAIT_OBJECT_0)
+	{
+		target_state_ = TargetState::Terminated;
+		dll_alive_ = false;
+		return;
+	}
+
+	// Still running: alive vs hung from the hook heartbeat (advances ~4x/s). A live
+	// process whose heartbeat stalled for ~2 s is frozen, not gone -- a distinct state.
+	const std::uint32_t hb = server_.hook_status().heartbeat;
+	const double now = ImGui::GetTime();
+	if (hb != last_heartbeat_)
+	{
+		last_heartbeat_ = hb;
+		last_heartbeat_time_ = now;
+		dll_alive_ = true;
+	}
+	else if (now - last_heartbeat_time_ > 2.0)
+	{
+		dll_alive_ = false;
+	}
+	target_state_ = dll_alive_ ? TargetState::Alive : TargetState::Hung;
+}
+
 void InjectionPanel::refresh_processes()
 {
 	processes_ = list_processes();
@@ -102,6 +160,14 @@ void InjectionPanel::inject_selected()
 	if (result.status == InjectStatus::Ok)
 	{
 		injected_ = true;
+		// Track liveness: a SYNCHRONIZE|QUERY handle lets us notice the game exiting,
+		// and seeding the heartbeat clock avoids a spurious "hung" before the first beat.
+		close_target_handle(); // drop any handle from a previous target
+		target_process_ = OpenProcess(SYNCHRONIZE | PROCESS_QUERY_LIMITED_INFORMATION, FALSE, selected_pid_);
+		target_state_ = TargetState::Alive;
+		last_heartbeat_ = 0;
+		last_heartbeat_time_ = ImGui::GetTime();
+		dll_alive_ = true;
 		status_ = "Injected into " + narrow(selected_name_) + " (pid " + std::to_string(selected_pid_) + ").";
 		status_color_ = kGreen;
 	}
@@ -273,19 +339,6 @@ void InjectionPanel::draw_hook_status(bool debug_details)
 
 	const HookStatusView status = server_.hook_status();
 
-	// DLL liveness from the heartbeat (advances ~4x/s while the worker runs).
-	const double now = ImGui::GetTime();
-	if (status.heartbeat != last_heartbeat_)
-	{
-		last_heartbeat_ = status.heartbeat;
-		last_heartbeat_time_ = now;
-		dll_alive_ = true;
-	}
-	else if (now - last_heartbeat_time_ > 1.5)
-	{
-		dll_alive_ = false;
-	}
-
 	ImGui::SeparatorText("Hook status");
 	if (!injected_)
 	{
@@ -293,17 +346,26 @@ void InjectionPanel::draw_hook_status(bool debug_details)
 		return;
 	}
 
-	if (dll_alive_)
+	switch (target_state_)
 	{
+	case TargetState::Alive:
 		ImGui::TextColored(kGreen, "Hook DLL loaded in pid %lu (heartbeat %u)", server_.target_pid(),
 		                   status.heartbeat);
-	}
-	else
-	{
-		ImGui::TextColored(kRed, "Hook DLL not responding (no heartbeat).");
+		break;
+	case TargetState::Hung:
+		ImGui::TextColored(kRed, "Target not responding -- heartbeat stalled (frozen?).");
+		break;
+	case TargetState::Terminated:
+		ImGui::TextColored(kRed, "Target process has exited.");
+		break;
+	case TargetState::NotInjected:
+		break;
 	}
 
+	// The game is gone or frozen -> its hooks can't act on toggles, so lock them.
+	ImGui::BeginDisabled(target_state_ != TargetState::Alive);
 	draw_subsystem_controls(status);
+	ImGui::EndDisabled();
 	ImGui::TextDisabled("Controller poll rates are in the Controllers panel.");
 
 	draw_hook_list(status);
@@ -348,11 +410,23 @@ void InjectionPanel::draw(bool debug_details)
 
 	if (server_.running())
 	{
-		ImGui::TextColored(kGreen, "Connected to pid %lu", server_.target_pid());
+		if (target_state_ == TargetState::Terminated)
+		{
+			ImGui::TextColored(kRed, "Target (pid %lu) has terminated.", server_.target_pid());
+		}
+		else if (target_state_ == TargetState::Hung)
+		{
+			ImGui::TextColored(kRed, "Target (pid %lu) is not responding.", server_.target_pid());
+		}
+		else
+		{
+			ImGui::TextColored(kGreen, "Connected to pid %lu", server_.target_pid());
+		}
 		if (ImGui::Button("Disconnect"))
 		{
 			server_.stop();
 			injected_ = false;
+			close_target_handle();
 			status_ = "Stopped.";
 			status_color_ = kGrey;
 		}
@@ -401,8 +475,9 @@ void InjectionPanel::draw(bool debug_details)
 		ImGui::TextColored(status_color_, "%s", status_.c_str());
 	}
 
-	// Synthetic input only reaches the game if the XInput hook is installed.
-	ImGui::BeginDisabled(injected_ && !want_input_);
+	// Synthetic input only reaches the game if the XInput hook is installed and the
+	// target is actually alive to receive it.
+	ImGui::BeginDisabled(injected_ && (!want_input_ || target_state_ != TargetState::Alive));
 	ImGui::Checkbox("Forward synthetic test input", &test_input_);
 	ImGui::EndDisabled();
 	if (test_input_)

host/src/injection_panel.hpp

@@ -16,10 +16,28 @@
 namespace coop
 {
 
+// Liveness of the injected target, surfaced in the UI so a dead/hung game is obvious.
+enum class TargetState
+{
+	NotInjected, // no hook loaded
+	Alive,       // process running and the hook heartbeat is advancing
+	Hung,        // process still exists but the heartbeat stalled (not responding)
+	Terminated,  // process has exited
+};
+
 class InjectionPanel
 {
 public:
 	InjectionPanel();
+	~InjectionPanel();
+
+	InjectionPanel(const InjectionPanel&) = delete;
+	InjectionPanel& operator=(const InjectionPanel&) = delete;
+
+	// Recompute target liveness (terminated / hung / alive). Call once per frame from
+	// the main loop, independent of panel visibility, so game_hwnd() and the mirror
+	// panels react to a dead target even while the Injection panel is hidden.
+	void tick();
 
 	// `debug_details` shows the verbose hook diagnostics (per-slot poll table,
 	// focus-API counts, input-path detection); off shows a general summary.
@@ -29,12 +47,24 @@ public:
 	// test-input mode is on, a synthetic pattern is sent instead of `pads`.
 	void publish(const std::array<PadInfo, kMaxPads>& pads);
 
-	// The injected game's main window, as reported by the hook (null if none).
+	// The injected game's main window, as reported by the hook (null if none). A
+	// terminated target's HWND is stale/invalid, so report none -- the capture and
+	// audio panels then drop to idle instead of chasing a dead window.
 	[[nodiscard]] HWND game_hwnd() const
 	{
+		if (target_state_ == TargetState::Terminated)
+		{
+			return nullptr;
+		}
 		return reinterpret_cast<HWND>(server_.hook_status().game_hwnd);
 	}
 
+	// Current liveness of the injected target (for other panels / status).
+	[[nodiscard]] TargetState target_state() const
+	{
+		return target_state_;
+	}
+
 	// The hook's full diagnostics back-channel (other panels read the audio
 	// render-stream counts from here).
 	[[nodiscard]] HookStatusView hook_status() const
@@ -78,6 +108,8 @@ public:
 private:
 	void refresh_processes();
 	void inject_selected();
+	void update_liveness();      // recompute target_state_ from process + heartbeat
+	void close_target_handle();  // close target_process_ and reset liveness state
 	void draw_subsystem_controls(const HookStatusView& status);
 	void draw_hook_list(const HookStatusView& status);
 	void draw_hook_status(bool debug_details);
@@ -105,6 +137,12 @@ private:
 	std::uint32_t last_heartbeat_ = 0;
 	double last_heartbeat_time_ = 0.0;
 	bool dll_alive_ = false;
+
+	// Target-process liveness: a SYNCHRONIZE|QUERY handle taken at inject time lets
+	// us notice the game exiting (WaitForSingleObject) vs merely hanging (heartbeat
+	// stalled while the process still exists).
+	HANDLE target_process_ = nullptr;
+	TargetState target_state_ = TargetState::NotInjected;
 };
 
 } // namespace coop

host/src/main.cpp

@@ -145,6 +145,7 @@ int run()
 #endif
 		input->poll();
 		injection.publish(input->pads());
+		injection.tick(); // refresh target liveness before the mirror panels read game_hwnd()
 		const HWND game = injection.game_hwnd();
 		capture.set_target(game);
 		audio.set_target(game);