Recipients build indexes after cloning, but the coordinator stays in the cloning  phase for that entire duration. Donor history is currently unpinned when the coordinator advances to applying, even though the retained history is only needed until all recipients finish cloning.

Long-running index builds can extend the time donor history remains pinned, increasing cache pressure and adding system pressure.

The coordinator needs a distinct building-index phase that begins once every recipient has finished cloning. This transition should advance the donors and trigger the existing history-unpinning behavior before index builds finish. A separate phase will also let the coordinator report index-build metrics independently from cloning metrics.