prometeu-runtime/discussion/workflow/plans/PLN-0144-suspend-resident-game-when-shell-takes-foreground.md

id	ticket	title	status	created	ref_decisions	tags
PLN-0144	foreground-stack-game-pause-shell-vm-backed	Suspend Resident Game When Shell Takes Foreground	open	2026-07-04	DEC-0037	runtime os lifecycle shell game vm foreground architecture

Briefing

DEC-0037 says a suspended resident Game must not receive normal gameplay ticks, normal Game input, or frame pacing while Hub/Shell owns foreground. The current set_shell_foreground path can mark the resident Game as PausedSuspended in the foreground stack while TaskManager::set_foreground only demotes the previous foreground Game task to Background. This creates a state mismatch if a Shell is opened while the Game has not already gone through the Home suspension path.

Objective

Make Shell foreground acquisition either require an already suspended resident Game or perform the necessary OS-owned suspension consistently across foreground stack, task manager, and process manager.

Dependencies

• Source decision: DEC-0037.
• Can be implemented independently of PLN-0142 and PLN-0143, but tests should be rerun with those fixes if they are executed first.

Scope

Included:

• Close the mismatch between ResidentGameState::PausedSuspended and TaskState::Background.
• Ensure Shell foreground cannot leave a resident Game running or backgrounded.
• Cover both create_vm_shell_task and create_native_shell_task paths.
• Preserve the rule that only one foreground Shell may exist.
• Keep the normal Home -> Shell flow working.

Excluded:

• No direct Shell -> Game return behavior; v1 still returns Shell close to Hub.
• No background Game execution.
• No multiple resident Games.
• No Shell persistence policy changes.

Non-Goals

• Do not broaden Shell lifecycle semantics.
• Do not implement Game-to-Game switching.
• Do not add UI controls for resume.

Execution Method

1. Define the legal Shell foreground precondition.

   • What changes: decide in code whether Shell foreground requires the resident Game to already be PausedSuspended, or whether set_shell_foreground_task is responsible for suspending it.
   • How it changes: prefer centralizing the invariant in LifecycleFacade::set_shell_foreground_task, because it owns task/process transitions.
   • File(s): crates/console/prometeu-system/src/os/facades/lifecycle.rs, crates/console/prometeu-system/src/services/foreground.rs.

2. Synchronize task/process state when Shell takes foreground.

   • What changes: if a resident Game exists and is not already suspended, mark the Game task and process Suspended before or during Shell foreground transition.
   • How it changes: use process_id_for_task for the resident Game and call task_manager.mark_suspended and process_manager.mark_suspended in the same lifecycle operation that sets Shell foreground.
   • File(s): crates/console/prometeu-system/src/os/facades/lifecycle.rs.

3. Tighten foreground stack behavior.

   • What changes: ForegroundStack::set_shell_foreground must not silently hide invalid state transitions.
   • How it changes: either reject Shell foreground when the resident Game is still Foreground/PauseRequested, or return enough information for the lifecycle facade to suspend the resident Game explicitly.
   • File(s): crates/console/prometeu-system/src/services/foreground.rs.

4. Add regression tests for reachable session paths.

   • What changes: create tests that call create_vm_shell_task and create_native_shell_task while a Game task is foreground.
   • How it changes: assert foreground owner is Shell, resident Game remains recorded, Game task state is Suspended, and Game process state is Suspended.
   • File(s): crates/console/prometeu-system/src/os/system_os.rs, crates/console/prometeu-firmware/src/firmware/firmware.rs if the firmware Home/Shell path needs coverage.

Acceptance Criteria

• A Shell foreground transition cannot leave the resident Game in TaskState::Background.
• Foreground stack state, task state, and process state agree that the resident Game is suspended while Shell is foreground.
• create_vm_shell_task and create_native_shell_task both preserve the invariant.
• Opening a second foreground Shell remains rejected.
• Closing Shell still returns to Hub/Home, not directly to Game.

Tests

• Unit tests in prometeu-system for set_shell_foreground_task with a resident foreground Game.
• Session facade tests for VM Shell and native Shell creation while a Game is resident.
• Existing firmware Shell close tests must continue to pass.
• Run cargo test -p prometeu-system foreground lifecycle shell.
• Run cargo test -p prometeu-firmware shell.
• Run discussion validate.

Affected Artifacts

• crates/console/prometeu-system/src/services/foreground.rs
• crates/console/prometeu-system/src/os/facades/lifecycle.rs
• crates/console/prometeu-system/src/os/facades/sessions.rs
• crates/console/prometeu-system/src/os/system_os.rs
• crates/console/prometeu-firmware/src/firmware/firmware.rs