ADR-0138: Operational settings gain an on/off kind

• Status: accepted
• Date: 2026-09-30
• Deciders: Mahdi Amirabdollahi

Context

Operational settings (ADR-0047) had three kinds: duration, integer and cron. The code said a fourth would be a design decision, because each kind is an input on the settings screen. The installation-wide MCP read-only mode (ADR-0137) is a switch, and a switch encoded as an integer (0/1) or a duration misleads whoever edits it.

Decision

We will add SettingDef.Kind.BOOLEAN, whose values are exactly true or false, read with SettingsService.bool(key). Operational configuration renders it as a switch that saves when flipped, with a Reset while overridden. SettingDef is plugin API, so plugins can declare one too.

Consequences

• Adding an enum constant is binary compatible. A plugin's exhaustive switch over Kind would need a new branch when rebuilt.
• The settings screen now has four inputs.

Alternatives considered

• An integer setting with min = 0 and max = 1. It reads as a number, and a wrong value is a typo rather than impossible.