When a peer restores a version, the file reloads to it. Edits made on
the replaced version stayed queued: their save failed for good and
locked the workspace, and a rollback or a rebase replayed them on the
restored data.
Loading another version forgets the queued, buffered and saved commits
made on the old one. A save of such a commit, in flight or answered, is
dropped instead of failing or being rolled back, and one save carries
the edits of one version only.
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