Select a block and ask for it cleaner, faster, or in a different pattern. The rewrite arrives as a diff against the selection, with the surrounding code left alone.
Because the index knows the call sites, a signature change offers to update them in the same pass rather than leaving you to find them. A rename that breaks a public export is reported instead of applied.
The common case is small and undramatic: a nested conditional flattened, a loop turned into a comprehension, a duplicated block extracted into the helper it should always have been.