Smart installer watchdog

[fdotcico]

Summary

Hi, loved you program!
This PR adds an optional smart installer and safety watchdog on top of the existing display_disable binary.

The goal is to improve the setup experience and reduce the risk of being left without an active built-in display when using a MacBook with an external monitor.

What changed

• Added scripts/install_smart.sh

  • installs display_disable if missing
  • detects the built-in display ID automatically
  • creates configurable shell aliases, defaulting to s-off and s-on
  • installs an optional LaunchAgent watchdog
  • creates a user-level watchdog configuration file

• Added scripts/auto_enable_builtin_on_external_disconnect.sh

  • checks display state periodically
  • re-enables the built-in display if it is disabled and no trusted external display is detected
  • handles generic or fallback display names such as Display and Unknown Display
  • supports lightweight logging, optional debug logging, and log rotation

• Added scripts/trust_current_external_displays.sh

  • lets users add currently connected external monitors to the trusted display list
  • useful for users who move between home, office, docks, or multiple monitor setups

• Added scripts/uninstall_smart.sh

  • removes the LaunchAgent, helper scripts, config, aliases, logs, and display_disable
  • also cleans up older LaunchAgent/script names from previous versions of this setup

• Updated README

  • preserves the original documentation
  • adds a section for the smart installer, watchdog, trusted displays, logs/retention, and uninstall behavior

Behavior

The smart setup is optional. The existing display_disable binary behavior is not changed.

The watchdog is conservative by default:

• check interval: 10 seconds
• unsafe confirmations: 2
• logging disabled by default
• debug logging disabled by default
• log rotation enabled when logging is used

If the built-in display is already active, the watchdog does nothing.

If the built-in display is disabled and a trusted external display is present, the watchdog does nothing.

If the built-in display is disabled and no trusted external display is detected, the watchdog waits for the configured number of confirmations before re-enabling the built-in display.

Why

When the built-in display is disabled and the external display is disconnected, macOS may still report a stale or generic external display entry. In that case, the user may be left without the built-in display enabled.

The watchdog provides a safety mechanism for this scenario.

Testing

Tested on macOS with Apple Silicon and an external monitor.

Verified:

• display_disable list detects the built-in display ID
• s-off disables the built-in display
• s-on re-enables the built-in display
• watchdog stays idle when a trusted external display is connected
• watchdog re-enables the built-in display when the external monitor is disconnected and macOS reports a generic fallback display
• trust-displays updates ~/.displaydisabler-watchdog.conf
• uninstall removes smart setup files, aliases, LaunchAgent, config, and binary