🧰 Task

Currently, #5869 #5852 #5871 have to type layer.mode as str, because fo some complexity.

• Layer base need to refer the a "self.mode",
• Each subclass has self.mode be a different type.
• The base class need to handle common logic.
• The runtime value of the Mode type is held in _modeclass

But all those does not help with type checking.

[I believe] we can solve that with generics, but this seem a bit hard to do that in the above mentioned PRs, so opening an issue to track this.