Under the hood
Setting a renamed settings key's old alias to null can now explicitly reset it instead of just being dropped
What
Some settings keys have both a current name and an older alias. Previously, setting the alias to null had one behavior. Now, when a special mode called loneNullAlias === 'rename' applies and the current (canonical) key has no value set, setting the alias to null is treated as an explicit reset: Claude Code writes null onto the canonical key before removing the alias. In other cases, the alias is just dropped as before.
Why
This lets a null on an old setting name still express 'clear this setting' after it has been renamed, instead of that intent getting lost.