Widening the settle window to tens of seconds (previous commit) made a
real gap much more likely to bite: apply() gated every source,
including 'optimistic', on _is_settling. /course/vs/0 backs several
independent washer selects (cycle, detergent quantity, softener
quantity, ...), so picking a second one while the first write's window
was still open -- routine within a ~43s window -- had its own
optimistic value silently dropped from the cache instead of shown,
recreating the exact "write doesn't seem to apply" symptom the guard
exists to prevent, just for whichever write lost the race.
Let source='optimistic' always bypass the gate; poll/sweep/observe
stay gated as before. mark_write_pending still re-arms the window
right after, so the newer write is protected going forward.
Marc Billow
85cca70b6b