User request: sample of more complex mutation validation

[aboodman]

See original request here: https://github.com/rocicorp/replicache-todo/issues/2.

This could make sense in Replidraw, for example, some upper limit on number of objects on page or something?

[aboodman]

Not exactly "validation", but this new createTodo mutator ensures that there are not duplicate sort fields by assigning the next highest value from all current values:

https://github.com/rocicorp/replicache-todo/blob/main/frontend/todo.ts#L44