if target_os = "emscripten" ClipboardContext is not defined and not set to NopClipboardContext;

I would be fine for it getting set to Nop, getting the clipboard works very differently in wasm/emscripten and very much out of this scope having to cross the JS/FFI boundary without web-sys available and getting navigator.clipboard.

But, it doesnt get defined at all and that makes the compiler unhappy.

#[cfg(not(any(
unix,
windows,
target_os = "macos",
target_os = "android",
target_os = "ios",
target_os = "emscripten"
)))]
pub type ClipboardContext = nop_clipboard::NopClipboardContext;

I think the condition is mixed up here.

Add this before please (under the TODOs for android and ios)
#[cfg(target_os = "emscripten")]
pub type ClipboardContext = nop_clipboard::NopClipboardContext;