crates/console/prometeu-firmware/src/firmware/firmware.rs

@@ -289,16 +289,29 @@ mod tests {
         }
 
         fn add_game(&self, name: &str, with_program: bool) -> PathBuf {
+            self.add_game_with_identity(name, 42, "Stress", "1.0.0", with_program)
+        }
+
+        fn add_game_with_identity(
+            &self,
+            name: &str,
+            app_id: u32,
+            title: &str,
+            app_version: &str,
+            with_program: bool,
+        ) -> PathBuf {
             let cart = self.path.join(name);
             fs::create_dir_all(&cart).expect("test cartridge should be created");
-            let manifest = r#"{
-                "magic": "PMTU",
-                "cartridge_version": 1,
-                "app_id": 42,
-                "title": "Stress",
-                "app_version": "1.0.0",
-                "app_mode": "Game"
-            }"#;
+            let manifest = format!(
+                r#"{{
+                    "magic": "PMTU",
+                    "cartridge_version": 1,
+                    "app_id": {app_id},
+                    "title": "{title}",
+                    "app_version": "{app_version}",
+                    "app_mode": "Game"
+                }}"#
+            );
             fs::write(cart.join("manifest.json"), manifest)
                 .expect("test manifest should be written");
             if with_program {
@@ -728,6 +741,72 @@ mod tests {
         );
     }
 
+    #[test]
+    fn hub_home_clicking_different_game_terminates_previous_resident_session() {
+        let root = TestGameRoot::new();
+        root.add_game("stress", true);
+        root.add_game_with_identity("zzz-dummy", 43, "Zzz Dummy", "1.0.0", true);
+
+        let (mut firmware, mut platform) = hub_home_firmware();
+        firmware.hub.set_game_library(discover_games_root(&root.path));
+        firmware.tick(&InputSignals::default(), &mut platform);
+
+        let stress_click =
+            InputSignals { f_signal: true, x_pos: 72, y_pos: 90, ..Default::default() };
+        firmware.tick(&stress_click, &mut platform);
+        firmware.tick(&InputSignals::default(), &mut platform);
+
+        let first_game_task = match &firmware.state {
+            FirmwareState::GameRunning(step) => step.task_id,
+            other => panic!("expected first GameRunning state, got {:?}", other),
+        };
+
+        firmware.request_home_from_host();
+        firmware.tick(&InputSignals::default(), &mut platform);
+        assert_eq!(firmware.os.lifecycle().resident_game_task(), Some(first_game_task));
+
+        firmware.tick(&InputSignals::default(), &mut platform);
+        let dummy_click =
+            InputSignals { f_signal: true, x_pos: 72, y_pos: 118, ..Default::default() };
+        firmware.tick(&dummy_click, &mut platform);
+
+        assert_eq!(firmware.os.lifecycle().task_state(first_game_task), Some(TaskState::Closed));
+        assert_eq!(
+            firmware.os.lifecycle().process_state_for_task(first_game_task),
+            Ok(ProcessState::Stopped)
+        );
+        assert_eq!(
+            firmware
+                .os
+                .sessions()
+                .vm_session_for_task(first_game_task)
+                .map(|session| session.task_id),
+            None
+        );
+
+        let second_game_task = firmware
+            .os
+            .lifecycle()
+            .resident_game_task()
+            .expect("replacement game should be resident");
+        assert_ne!(second_game_task, first_game_task);
+        assert_eq!(
+            firmware
+                .os
+                .sessions()
+                .vm_session_for_task(second_game_task)
+                .map(|session| session.app_id),
+            Some(43)
+        );
+
+        firmware.tick(&InputSignals::default(), &mut platform);
+
+        match &firmware.state {
+            FirmwareState::GameRunning(step) => assert_eq!(step.task_id, second_game_task),
+            other => panic!("expected replacement GameRunning state, got {:?}", other),
+        }
+    }
+
     #[test]
     fn invalid_games_root_candidate_is_omitted_from_home_launch_boundary() {
         let root = TestGameRoot::new();

crates/console/prometeu-firmware/src/firmware/firmware_step_hub_home.rs

@@ -69,16 +69,18 @@ impl HubHomeStep {
                                 return Some(FirmwareState::ResumeResidentGame);
                             }
 
-                            ctx.os.log(
-                                LogLevel::Warn,
-                                LogSource::Hub,
-                                0,
-                                format!(
-                                    "Cannot launch Home game {} while resident game app_id {} is active",
-                                    cartridge.title, resident_app_id
-                                ),
-                            );
-                            return None;
+                            if let Err(error) = ctx.os.lifecycle().terminate_resident_game() {
+                                ctx.os.log(
+                                    LogLevel::Error,
+                                    LogSource::Hub,
+                                    0,
+                                    format!(
+                                        "Failed to terminate resident game app_id {} before launching {}: {:?}",
+                                        resident_app_id, cartridge.title, error
+                                    ),
+                                );
+                                return None;
+                            }
                         }
 
                         return Some(FirmwareState::LoadCartridge(LoadCartridgeStep::new(

crates/console/prometeu-system/src/os/facades/lifecycle.rs

@@ -222,6 +222,28 @@ impl<'a> LifecycleFacade<'a> {
         Ok(())
     }
 
+    pub fn terminate_resident_game(&mut self) -> Result<Option<TaskId>, LifecycleError> {
+        let Some(task_id) = self.os.foreground_stack.resident_game_task() else {
+            return Ok(None);
+        };
+
+        let process_id = process_id_for_task(self.os, task_id)?;
+
+        self.os.task_manager.close_task(task_id);
+        self.os.process_manager.mark_stopped(process_id);
+        self.os.foreground_stack.clear_resident_game(task_id);
+        self.os.vm_sessions.remove_for_task(task_id);
+        self.os.game_lifecycle_events.retain(|event| event.task_id != task_id);
+
+        if matches!(self.os.foreground_stack.owner(), ForegroundOwner::Game(owner) if owner == task_id)
+        {
+            self.os.foreground_stack.return_to_hub();
+            self.os.task_manager.clear_foreground();
+        }
+
+        Ok(Some(task_id))
+    }
+
     pub fn crash_task(
         &mut self,
         task_id: TaskId,

crates/console/prometeu-system/src/os/system_os.rs

@@ -218,6 +218,42 @@ mod tests {
         );
     }
 
+    #[test]
+    fn terminate_resident_game_closes_task_and_removes_vm_session() {
+        let mut os = SystemOS::new(None);
+        let game = os.sessions().create_vm_game_task(42, "Sector Crawl");
+
+        os.lifecycle().request_home_from_game(game).expect("home request should succeed");
+        assert_eq!(os.lifecycle().pending_game_lifecycle_events().len(), 1);
+
+        assert_eq!(os.lifecycle().terminate_resident_game(), Ok(Some(game)));
+
+        assert_eq!(os.lifecycle().resident_game(), None);
+        assert_eq!(os.lifecycle().foreground_owner(), ForegroundOwner::Hub);
+        assert_eq!(os.lifecycle().task_state(game), Some(TaskState::Closed));
+        assert_eq!(process_state_for_task(&os, game), ProcessState::Stopped);
+        assert_eq!(os.sessions().vm_session_for_task(game).map(|session| session.task_id), None);
+        assert!(os.lifecycle().pending_game_lifecycle_events().is_empty());
+    }
+
+    #[test]
+    fn terminate_resident_game_preserves_foreground_shell() {
+        let mut os = SystemOS::new(None);
+        let game = os.sessions().create_vm_game_task(42, "Sector Crawl");
+        os.lifecycle().request_home_from_game(game).expect("home request should succeed");
+        os.lifecycle().advance_game_pause_budget(game).expect("budget should expire");
+        let shell = os.sessions().create_vm_shell_task(7, "Settings");
+
+        assert_eq!(os.lifecycle().terminate_resident_game(), Ok(Some(game)));
+
+        assert_eq!(os.lifecycle().foreground_owner(), ForegroundOwner::Shell(shell));
+        assert_eq!(os.lifecycle().resident_game(), None);
+        assert_eq!(os.lifecycle().task_state(game), Some(TaskState::Closed));
+        assert_eq!(process_state_for_task(&os, game), ProcessState::Stopped);
+        assert_eq!(os.sessions().vm_session_for_task(game).map(|session| session.task_id), None);
+        assert_eq!(os.lifecycle().task_state(shell), Some(TaskState::Foreground));
+    }
+
     #[test]
     fn vm_game_task_creates_vm_session() {
         let mut os = SystemOS::new(None);

crates/console/prometeu-system/src/services/vm_session.rs

@@ -121,6 +121,10 @@ impl VmSessionRegistry {
         self.get_mut(VmSessionId(task_id))
     }
 
+    pub fn remove_for_task(&mut self, task_id: TaskId) -> Option<VmSession> {
+        self.sessions.remove(&VmSessionId(task_id))
+    }
+
     pub fn resident_game(&self) -> Option<&VmSession> {
         self.sessions.values().find(|session| session.app_mode == AppMode::Game)
     }
@@ -231,6 +235,31 @@ mod tests {
         assert_eq!(registry.resident_game_for_app(43).map(|session| session.task_id), None);
     }
 
+    #[test]
+    fn remove_for_task_removes_only_matching_session() {
+        let game_process = Process::new(ProcessId(1), 42, "Stress", ProcessKind::VmGame);
+        let game_task = Task::new(TaskId(7), game_process.id, 42, "Stress", TaskKind::Game);
+        let shell_process = Process::new(ProcessId(2), 9, "Shell", ProcessKind::VmShell);
+        let shell_task = Task::new(TaskId(8), shell_process.id, 9, "Shell", TaskKind::Shell);
+        let mut registry = VmSessionRegistry::new();
+
+        registry
+            .create_for_task(&game_task, &game_process, "", None, Arc::new(AtomicU32::new(0)))
+            .expect("game session should create");
+        registry
+            .create_for_task(&shell_task, &shell_process, "", None, Arc::new(AtomicU32::new(0)))
+            .expect("shell session should create");
+
+        let removed = registry.remove_for_task(game_task.id).expect("game session should remove");
+
+        assert_eq!(removed.task_id, game_task.id);
+        assert_eq!(registry.for_task(game_task.id).map(|session| session.task_id), None);
+        assert_eq!(
+            registry.for_task(shell_task.id).map(|session| session.task_id),
+            Some(shell_task.id)
+        );
+    }
+
     #[test]
     fn session_runtime_state_is_independent_per_session() {
         let game_process = Process::new(ProcessId(1), 42, "Stress", ProcessKind::VmGame);

discussion/index.ndjson

@@ -1,5 +1,5 @@
 {"type":"meta","next_id":{"DSC":44,"AGD":47,"DEC":40,"PLN":163,"LSN":53,"CLSN":1}}
-{"type":"discussion","id":"DSC-0043","status":"in_progress","ticket":"system-os-cartridge-switch-orchestrator","title":"SystemOS Cartridge Switch Orchestrator","created_at":"2026-07-03","updated_at":"2026-07-05","tags":["runtime","os","lifecycle","game","cartridge","architecture"],"agendas":[{"id":"AGD-0044","file":"AGD-0044-systemos-cartridge-switch-orchestrator.md","status":"accepted","created_at":"2026-07-03","updated_at":"2026-07-05"}],"decisions":[{"id":"DEC-0039","file":"DEC-0039-systemos-game-cartridge-switch-orchestrator.md","status":"accepted","created_at":"2026-07-05","updated_at":"2026-07-05","ref_agenda":"AGD-0044"}],"plans":[{"id":"PLN-0157","file":"PLN-0157-introduce-systemos-game-switch-target-contract.md","status":"done","created_at":"2026-07-05","updated_at":"2026-07-05","ref_decisions":["DEC-0039"]},{"id":"PLN-0158","file":"PLN-0158-terminate-resident-game-before-switching-cartridges.md","status":"open","created_at":"2026-07-05","updated_at":"2026-07-05","ref_decisions":["DEC-0039"]},{"id":"PLN-0159","file":"PLN-0159-recover-failed-game-switches-back-to-home.md","status":"open","created_at":"2026-07-05","updated_at":"2026-07-05","ref_decisions":["DEC-0039"]},{"id":"PLN-0160","file":"PLN-0160-add-dummy-boy-visual-switch-test-cartridge.md","status":"open","created_at":"2026-07-05","updated_at":"2026-07-05","ref_decisions":["DEC-0039"]},{"id":"PLN-0161","file":"PLN-0161-validate-stress-to-dummy-boy-game-switch-end-to-end.md","status":"open","created_at":"2026-07-05","updated_at":"2026-07-05","ref_decisions":["DEC-0039"]},{"id":"PLN-0162","file":"PLN-0162-specify-game-switch-contract-and-direct-boot-separation.md","status":"open","created_at":"2026-07-05","updated_at":"2026-07-05","ref_decisions":["DEC-0039"]}],"lessons":[]}
+{"type":"discussion","id":"DSC-0043","status":"in_progress","ticket":"system-os-cartridge-switch-orchestrator","title":"SystemOS Cartridge Switch Orchestrator","created_at":"2026-07-03","updated_at":"2026-07-05","tags":["runtime","os","lifecycle","game","cartridge","architecture"],"agendas":[{"id":"AGD-0044","file":"AGD-0044-systemos-cartridge-switch-orchestrator.md","status":"accepted","created_at":"2026-07-03","updated_at":"2026-07-05"}],"decisions":[{"id":"DEC-0039","file":"DEC-0039-systemos-game-cartridge-switch-orchestrator.md","status":"accepted","created_at":"2026-07-05","updated_at":"2026-07-05","ref_agenda":"AGD-0044"}],"plans":[{"id":"PLN-0157","file":"PLN-0157-introduce-systemos-game-switch-target-contract.md","status":"done","created_at":"2026-07-05","updated_at":"2026-07-05","ref_decisions":["DEC-0039"]},{"id":"PLN-0158","file":"PLN-0158-terminate-resident-game-before-switching-cartridges.md","status":"done","created_at":"2026-07-05","updated_at":"2026-07-05","ref_decisions":["DEC-0039"]},{"id":"PLN-0159","file":"PLN-0159-recover-failed-game-switches-back-to-home.md","status":"open","created_at":"2026-07-05","updated_at":"2026-07-05","ref_decisions":["DEC-0039"]},{"id":"PLN-0160","file":"PLN-0160-add-dummy-boy-visual-switch-test-cartridge.md","status":"open","created_at":"2026-07-05","updated_at":"2026-07-05","ref_decisions":["DEC-0039"]},{"id":"PLN-0161","file":"PLN-0161-validate-stress-to-dummy-boy-game-switch-end-to-end.md","status":"open","created_at":"2026-07-05","updated_at":"2026-07-05","ref_decisions":["DEC-0039"]},{"id":"PLN-0162","file":"PLN-0162-specify-game-switch-contract-and-direct-boot-separation.md","status":"open","created_at":"2026-07-05","updated_at":"2026-07-05","ref_decisions":["DEC-0039"]}],"lessons":[]}
 {"type":"discussion","id":"DSC-0039","status":"abandoned","ticket":"render-pipeline-family-and-future-3d","title":"Render Pipeline Family and Future 3D","created_at":"2026-06-04","updated_at":"2026-06-04","tags":["gfx","renderer","runtime","architecture","pipeline"],"agendas":[{"id":"AGD-0039","file":"AGD-0039-render-pipeline-family-and-future-3d.md","status":"abandoned","created_at":"2026-06-04","updated_at":"2026-06-04","_override_reason":"User explicitly chose to close this agenda without a new decision because DSC-0038 already established enough architecture for future extension, and 3D is intentionally deferred."}],"decisions":[],"plans":[],"lessons":[],"_override_reason":"User explicitly chose to close this agenda without a new decision because DSC-0038 already established enough architecture for future extension, and 3D is intentionally deferred."}
 {"type":"discussion","id":"DSC-0040","status":"done","ticket":"vm-render-parallel-execution-boundary","title":"VM and Render Parallel Execution Boundary","created_at":"2026-06-04","updated_at":"2026-06-06","tags":["runtime","renderer","vm","concurrency","architecture","perf"],"agendas":[],"decisions":[],"plans":[],"lessons":[{"id":"LSN-0048","file":"discussion/lessons/DSC-0040-vm-render-parallel-execution-boundary/LSN-0048-render-workers-need-a-closed-packet-contract.md","status":"done","created_at":"2026-06-06","updated_at":"2026-06-06"}]}
 {"type":"discussion","id":"DSC-0041","status":"done","ticket":"foreground-stack-game-pause-shell-vm-backed","title":"Foreground Stack, Game Pause, and VM-Backed Shell Coexistence","created_at":"2026-06-05","updated_at":"2026-07-05","tags":["runtime","os","lifecycle","shell","game","vm","foreground","architecture"],"agendas":[],"decisions":[],"plans":[],"lessons":[{"id":"LSN-0052","file":"discussion/lessons/DSC-0041-foreground-stack-game-pause-shell-vm-backed/LSN-0052-foreground-ownership-and-vm-session-ownership-are-separate.md","status":"done","created_at":"2026-07-05","updated_at":"2026-07-05"}]}

discussion/workflow/plans/PLN-0158-terminate-resident-game-before-switching-cartridges.md

@@ -2,7 +2,7 @@
 id: PLN-0158
 ticket: system-os-cartridge-switch-orchestrator
 title: Terminate Resident Game Before Switching Cartridges
-status: open
+status: done
 created: 2026-07-05
 ref_decisions: [DEC-0039]
 tags: [runtime, os, lifecycle, game, cartridge, architecture]