If the Context is unsupported (satisfies either AsyncContext or Context), a descriptive error is either thrown (sync) or returned via on-error callback (async).
This is important for core.async users, which is not supported oob in the future. Without this, the caller would never get any response if the core.async support was not enabled.
Don't pass the on-complete and on-error via the context, just not needed.
AsyncContextorContext), a descriptive error is either thrown (sync) or returned viaon-errorcallback (async).core.asyncusers, which is not supported oob in the future. Without this, the caller would never get any response if thecore.asyncsupport was not enabled.on-completeandon-errorvia the context, just not needed.