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

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)).

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

The central dispatcher checks action requirements before execution. As implemented in src/bridge.ts at lines 1231-1240, the code validates whether an action requires foreground focus:

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)).

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)).

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 (lines 7-76): Parses the headless flag from configuration and environment variables
• src/actions.ts (lines 95-98): Determines when an action usesCurrentFocus or needsForeground
• src/bridge.ts (lines 1231-1240): Central dispatcher that blocks foreground-requiring actions when headless is true
• docs/configuration.md (lines 50-60): Documents the headless option for users

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

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, 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 (lines 95-98), actions are defined with boolean flags indicating whether they useCurrentFocus or needForeground. The bridge in 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 (lines 7-76), which parses the headless flag from configuration files or environment variables. The setting is also documented in docs/configuration.md (lines 50-60) for user reference, and consumed by the bridge logic to enforce restrictions.

{
  "mcpServers": {
    "instagit": {
      "command": "npx",
      "args": ["-y", "instagit@latest"]
    }
  }
}