There are a few instances where it can be ambiguous whether an async function has completed:

1. Error handling — the example uses errdefer if (!awaited_download_frame) { but this can be converted to be errdefer if (!@frameState(download_frame).awaited) {
2. Generators — liveness is an indicator of completion, but there's currently not a way for the execution context to check

It'd be nice if we could check the "state" of the async function. Braindump:

const FrameState = struct {
    running: bool, // not sure if we should expose "suspended" as it sounds like a concurrent problem
    awaited: bool,
};

@frameState(f: anyframe) FrameState