Reloading the open file (a peer's restore, the fallback of a rollback)
runs initialize-workspace again without leaving the workspace. The
streams the first run started kept running next to the new ones, so a
commit added one undo entry per reload and each notification was
handled twice. The old subscription also sent its unsubscribe after the
new subscribe, which ended the new one on the server.
A new initialize-workspace, text reflow, shape layout or notification
subscription stops the one before it, and a subscription replaced by
one to the same file sends no unsubscribe.
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