Closes the one coverage gap from the final review: the spec's
'one async call per session' efficiency claim is now directly
verified via the reviewer call count, not just implied. Also drops a
stale CarryForward-preview mention from the Review projection in the
design spec to match the shipped (cleaner) behaviour.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
felixm