# How Headless Mode Restrictions in Pi-Computer-Use Prevent Window Activation and Cursor Movement

> Discover how pi-computer-use headless mode restrictions block window activation and cursor movement. Understand the headless boundary and foreground focus changes.

- Repository: [injaneity/pi-computer-use](https://github.com/injaneity/pi-computer-use)
- Tags: deep-dive
- Published: 2026-07-16

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**Pi-Computer-Use enforces a strict-headless boundary that blocks window activation, cursor movement, and foreground focus changes when running in headless mode.**

The `pi-computer-use` repository provides an automation framework designed to operate without interfering with the user's visible desktop state. When configured with `headless: true`, the system implements strict boundaries to prevent any UI changes, ensuring the agent can observe and reason about the interface without disrupting the user's workflow.

## Understanding the Strict-Headless Boundary

The headless mode in pi-computer-use establishes a **strict-headless boundary** that forbids any operation affecting the user's visible desktop state. According to the architecture documentation, this boundary ensures that "with `headless: true`, the background boundary is strict: Pi must never … **move the global cursor**, … or display the agent cursor" (source: [[`docs/architecture.md`](https://github.com/injaneity/pi-computer-use/blob/main/docs/architecture.md#L109)](https://github.com/injaneity/pi-computer-use/blob/main/docs/architecture.md#L109)).

This restriction applies to three critical areas: window activation, cursor movement, and raw input posting. The system checks these constraints before dispatching any UI action, rejecting operations that would violate the headless contract.

## Blocking Window Activation and Focus Changes

When running in headless mode, the engine **never brings background applications to the foreground** or changes which window has focus. This restriction is enforced by the bridge logic that evaluates whether an action can be safely executed without affecting the desktop state.

### The Foreground Guard in [`src/bridge.ts`](https://github.com/injaneity/pi-computer-use/blob/main/src/bridge.ts)

The central dispatcher checks action requirements before execution. As implemented in [`src/bridge.ts`](https://github.com/injaneity/pi-computer-use/blob/main/src/bridge.ts) at lines 1231-1240, the code validates whether an action requires foreground focus:

```typescript
if ((action.usesCurrentFocus || action.needsForeground) && !headless) { … }

```

If an action sets `usesCurrentFocus` or `needsForeground` to true while `headless` is enabled, the system rejects the operation. This guard ensures that **no window raising or activation** occurs when the user has configured headless mode. The `act_ui.headless` flag determines whether foreground execution is prohibited (source: [[`docs/architecture.md`](https://github.com/injaneity/pi-computer-use/blob/main/docs/architecture.md#L111)](https://github.com/injaneity/pi-computer-use/blob/main/docs/architecture.md#L111)).

## Preventing Global Cursor Movement

Headless mode explicitly **blocks global cursor movement** to prevent any visual disruption. On macOS, the system normally supports a cursor overlay feature, but this is suppressed when `headless: true` is set. The architecture documentation states that in headless mode, the system cannot "move the global cursor" or "display the agent cursor" (source: [[`docs/architecture.md`](https://github.com/injaneity/pi-computer-use/blob/main/docs/architecture.md#L109)](https://github.com/injaneity/pi-computer-use/blob/main/docs/architecture.md#L109)).

This means that synthetic mouse events are never emitted to the OS, and the agent cannot perform actions that would reposition the user's cursor. Low-level HID events—including mouse clicks and key presses—are blocked from being posted unless the action can complete without changing focus or cursor state.

## Configuration and Implementation

The headless restriction spans multiple files in the codebase:

- **[`src/config.ts`](https://github.com/injaneity/pi-computer-use/blob/main/src/config.ts)** (lines 7-76): Parses the `headless` flag from configuration and environment variables
- **[`src/actions.ts`](https://github.com/injaneity/pi-computer-use/blob/main/src/actions.ts)** (lines 95-98): Determines when an action `usesCurrentFocus` or `needsForeground`
- **[`src/bridge.ts`](https://github.com/injaneity/pi-computer-use/blob/main/src/bridge.ts)** (lines 1231-1240): Central dispatcher that blocks foreground-requiring actions when headless is true
- **[`docs/configuration.md`](https://github.com/injaneity/pi-computer-use/blob/main/docs/configuration.md)** (lines 50-60): Documents the `headless` option for users

When implementing headless mode, configure the flag through the configuration system:

```typescript
import { getComputerUseConfig, act } from "pi-computer-use";

// Enable headless mode via config
const cfg = getComputerUseConfig();
cfg.headless = true;

// Attempt a click that would normally activate a window
try {
  await act({ type: "click", selector: "#submit" });
} catch (e) {
  console.error("Action rejected in headless mode:", e);
}

// In headless mode the cursor overlay is suppressed
await act({
  type: "move",
  direction: "right",
  distance: 100,
  // This will be a no-op because the global cursor cannot move
});

```

## Summary

- **Strict-headless boundary**: Prevents any operation that affects visible desktop state when `headless: true` is configured.
- **Window activation blocked**: The bridge rejects actions with `usesCurrentFocus` or `needsForeground` flags to prevent bringing windows to the front.
- **Cursor movement restricted**: Global cursor positioning is disabled, and the macOS cursor overlay is suppressed to avoid visual disruption.
- **Low-level input blocked**: Raw HID events are prevented from posting to the OS when they would change focus or cursor state.

## Frequently Asked Questions

### What happens if an action requires foreground focus in headless mode?

The action is rejected by the bridge dispatcher. According to the logic in [`src/bridge.ts`](https://github.com/injaneity/pi-computer-use/blob/main/src/bridge.ts), if an action has `usesCurrentFocus` or `needsForeground` set to true while `headless` is enabled, the system prevents execution and typically throws an error or returns a rejection, ensuring no window activation occurs.

### Can the cursor overlay be enabled in headless mode on macOS?

No. The cursor overlay is explicitly suppressed when `headless: true`. The architecture documentation confirms that displaying the agent cursor is forbidden under the strict-headless boundary, even though the feature is available when running in non-headless mode.

### How does the bridge determine if an action needs foreground execution?

The bridge checks the action's metadata properties. In [`src/actions.ts`](https://github.com/injaneity/pi-computer-use/blob/main/src/actions.ts) (lines 95-98), actions are defined with boolean flags indicating whether they `useCurrentFocus` or `needForeground`. The bridge in [`src/bridge.ts`](https://github.com/injaneity/pi-computer-use/blob/main/src/bridge.ts) evaluates these flags against the `headless` configuration before dispatching.

### Where is the headless mode configured?

Headless mode is configured in [`src/config.ts`](https://github.com/injaneity/pi-computer-use/blob/main/src/config.ts) (lines 7-76), which parses the `headless` flag from configuration files or environment variables. The setting is also documented in [`docs/configuration.md`](https://github.com/injaneity/pi-computer-use/blob/main/docs/configuration.md) (lines 50-60) for user reference, and consumed by the bridge logic to enforce restrictions.