Bound the empty-upstream suspension read by --wait-timeout

Trail finding 01M1VQ779H5B: the probe read the raw ctx, so it could hang past a deadline the caller had set — and past the doc comment this branch added, which promises opts.timeout covers the whole operation on both routes. Every other call in createAndAwaitMirror already uses waitCtx.

The branch is only reachable through the deprecated empty flag the server no longer sets, so the test hand-builds that response; it hangs for 5s against the old code and returns in 50ms against the fixed one.

Also reflows the applyAsyncSuspension comment paragraph whose ragged wrap Copilot flagged.