* fix(cli): an update never replaces the CLI's files while a hyperframes command is running
* fix(cli): a killed command's leftover pid file cannot hold updates back
* fix(cli): judge a stale pid file by the installer's own clock, so sleep cannot drop a live command
* fix(cli): after a sleep the installer watches every command's file afresh
* docs(cli): shorten the installer script comment
* docs(cli): keep the new files within their comment share
* refactor(cli): split the upgrade eligibility check out of the installer scheduler
* docs(cli): keep the scheduler's doc on the scheduler