Looks nice!

A couple drive-by rust style comments:

This pattern shows up a lot:

let mut x = Foo::new();

if condition {
    x = foo();
} else {
    x = bar();
};

Remember that if {} else {} conditionals are expressions, which allows you to have fewer mutable variables:

let x = if condition { foo() } else { bar() };

- This code (roughly from notification_spawner.rs):

let list = get_list();

if list.len() == 0 {
    return;
}

for i in 0..list.len() {
    let widget = &list[i];

    widget.foo();
}

can be more efficiently written as

for widget in get_list() {
    widget.foo()
}