ADR-013: Single mutation authority

Context

The shell-era adapters combine calculation, application and reloads. ADR-004 and ADR-005 remain the compatibility contract, not authority for plugins to apply files.

Decision

Only core owns production writes, backups, recovery, registration, package installs and process signals. Plugins calculate proposals and write only staged artifacts. No plugin remains running during core commit. Effects are typed requests, never shell strings. Unimplemented effects fail closed. A plugin's validation is advisory.

The restricted hello profile proves this boundary with one exact sync:managed-root:required effect. The plugin may request it, but only core interprets and executes it after a durable commit. The request contains no command, path, PID or arbitrary argument. This narrow driver does not authorize production terminal reloads or callbacks into a plugin.

The first implementation is an opt-in hello profile in a newly created private directory, separate from dot theme and all existing workstation commands. Its two non-secret text outputs demonstrate the boundary without migrating user files.

Consequences and acceptance

The default command surface is unchanged. The prototype is not production-ready or an OS sandbox. Tests must show plugin failure cannot reach commit, and recovery works with the plugin deleted. Migration requires full ownership inventories, production containment, equivalence tests and separately reviewed platform drivers.