---
id: PLN-0130
ticket: system-run-cart
title: Remove Runtime Run Cart Stub Dispatch
status: done
created: 2026-07-03
ref_decisions: [DEC-0035]
tags: []
---

## Briefing

`DEC-0035` forbids a callable userland `system.run_cart` stub. This plan covers
runtime and VM dispatch cleanup so obsolete calls cannot silently succeed.
Public ABI removal is handled by `PLN-0129`; direct boot preservation is handled
by `PLN-0131`.

## Objective

Remove the runtime no-op dispatch path for `SystemRunCart` and ensure stale or
obsolete userland attempts fail explicitly rather than returning success.

## Dependencies

- Source decision: `DEC-0035`.
- Depends on the ABI direction in `PLN-0129`, but can be implemented in the same
  PR if the public enum/registry removal and dispatch cleanup move together.

## Scope

- Remove the `Syscall::SystemRunCart => return Ok(())` path from
  `crates/console/prometeu-system/src/services/vm_runtime/dispatch.rs`.
- Update any match arms made unreachable or obsolete by removing
  `SystemRunCart`.
- Ensure stale numeric syscall ids or stale bytecode declarations fail with the
  repository's existing unknown/invalid syscall behavior.
- Add negative coverage for userland attempts to invoke the removed operation,
  using the closest existing VM runtime syscall tests.

## Non-Goals

- Do not implement a replacement navigation operation.
- Do not implement the `Home -> another Game` orchestrator.
- Do not alter direct host/CLI/debug cartridge boot paths.
- Do not change `system.has_cart` behavior unless required by compile fallout.

## Execution Method

1. Inspect `dispatch.rs` for all `SystemRunCart` match arms.
2. Remove the no-op success path and any unreachable arms tied only to
   `SystemRunCart`.
3. If the public enum variant is removed by `PLN-0129`, update exhaustiveness
   and registry mapping accordingly.
4. Add or update VM runtime tests that demonstrate `system.run_cart` is not
   callable from guest/userland.
5. Run targeted runtime tests and compile checks.

## Acceptance Criteria

- There is no runtime path where a guest `system.run_cart` call returns `Ok(())`.
- Stale/obsolete attempts fail explicitly through existing invalid syscall or
  declaration validation behavior.
- `system.has_cart` and unrelated system syscalls keep their current behavior.
- Runtime dispatch remains exhaustive and clear after removing `SystemRunCart`.

## Tests

- Add a negative test in `crates/console/prometeu-system/src/services/vm_runtime`
  for stale userland `run_cart` attempts, if the test harness can express it.
- Run `cargo test` for `prometeu-system` and any impacted syscall crates.
- Run a workspace compile/test command if targeted tests reveal cross-crate enum
  fallout.

## Affected Artifacts

- `crates/console/prometeu-system/src/services/vm_runtime/dispatch.rs`
- `crates/console/prometeu-system/src/services/vm_runtime/tests.rs`
- `crates/console/prometeu-hal/src/syscalls.rs`
- `crates/console/prometeu-hal/src/syscalls/registry.rs`