> For the complete documentation index, see [llms.txt](https://carec.gitbook.io/carec-docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://carec.gitbook.io/carec-docs/documentation/architecture/mode-and-command-arbitration.md).

# Mode and Command Arbitration

CAREC supports multiple ways to request movement, but only one bounded command path may reach the wheelchair drive interface.

| Source                        | Purpose                             | Priority principle      |
| ----------------------------- | ----------------------------------- | ----------------------- |
| Emergency stop                | Request the defined no-motion state | Highest                 |
| Manual or alternative control | Direct user mobility                | Higher than autonomy    |
| Caregiver takeover            | Supervised intervention             | Higher than autonomy    |
| Assisted functions            | Modify unsafe manual commands       | Safety-limited          |
| Autonomous planner            | Propose a trajectory                | Lowest motion authority |

```mermaid
flowchart TD
    E["Emergency stop"] --> A["Command arbitrator"]
    M["Manual input"] --> A
    C["Caregiver takeover"] --> A
    N["Autonomous planner"] --> A
    A --> S["Safety supervisor"]
    S --> D["Bounded drive command"]
```

Mode must be explicit and visible. Stale, repeated, or invalid commands are rejected. Manual takeover cancels autonomy. A restart never resumes prior motion automatically, and ambiguous command authority produces a safe-state transition.


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