`HttpClientImpl::send` transforms thrown exceptions to `IOException`'s, as documented in its spec:

     * @throws IOException if an I/O error occurs when sending or receiving, or
     * the client has {@linkplain ##closing shut down}

`sendAsync()` has a similar spec:

     * <p> The returned completable future completes exceptionally with:
     * <ul>
     * <li>{@link IOException} - if an I/O error occurs when sending or receiving,
     * or the client has {@linkplain ##closing shut down}.</li>

Yet it doesn't have this exception translation logic and propagates unchecked exceptions as is[1], which is against the spec.

[1] https://github.com/openjdk/jdk/pull/26155#discussion_r2235104122