The last registration wins, and a handle only removes its own

Registering a name already in use replaces the earlier registration, with no error and no warning. Re-registering a namespace replaces it whole. Every registration returns a handle, and unregister() removes the entry only if it is still the one that handle created.

The identity check is what makes silent overwrites safe. A hot-reloaded feature registers /brush.grow again, then the old copy disconnects and calls unregister(). Without the check that call would delete the live command.

Built-ins follow the same rule, as ui's built-in metrics and icons do (ui ADR-0016). /clear, /help and the host's theme are registered through the public API, and a host or editor can overwrite any of them.

Considered Options

• Throwing on a duplicate name. Hot reload would throw on every save, and the order in which hosts and editors register would become part of the API.
• Warning on a duplicate name. Every reload would log noise that nobody acts on.

Consequences

A running command's ctx.signal aborts when its registration is removed or replaced while the run is pending, so a command can stop work that belongs to code that is gone.