See PHI1808. Currently, "arc land <some bookmark>" does not destroy the bookmark in Mercurial. There are three issues here:
- "hg rebase --keep --collapse" moves bookmarks to the rewritten commits;
- "hg strip" moves bookmarks backwards;
- "hg prune" moves bookmarks backwards.
To get around "hg rebase", save and restore bookmark state.
To get around "hg strip" and "hg prune", explicitly destroy bookmarks pointing at commits before we strip/prune those commits.