A delete removes the leaf's metadata, so the KV number restarts at 1. A login
made right after a delete, before the next poll, was version 1 again and
looked no newer than the recorded 1, so it never installed. The version file
now records the store's write time next to the number and a later write
installs whatever its number. A record from before the time was kept falls
back to the number and gets its time when the same number is read again.
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