Planning from a mapping of a clone of the locked descriptor shared its
flock: a process forked by another thread meanwhile (any Command) kept the
lock alive for a moment after the editor was dropped, and a test that
reopened the file at once saw Error::Locked (once in a full run). On Linux
plan through /proc/self/fd (a new open file description of the same
file, which still follows a rename); elsewhere keep the clone.
Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>