- install and Reset retire the channels they replace: a retired daily
writer appends a late record and closes the file again, so no record is
lost and no descriptor stays open; diary.Close keeps reopening the
installed writers on the next record
- ApplyGlobals holds the setup lock for its whole run (lock-free
installLocked and setVerbosityLocked), so concurrent calls rebuild the
channels once (WR-06)
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