Edits invalidated the display caches, but the debounced snapshot
upload (150 ms) landed later - meanwhile the viewer had already
rendered and cached a proxy through the stale snapshot, and nothing
invalidated it again, so a paused monitor kept the pre-edit picture
until the playhead moved. Re-invalidate when the fresh snapshot is
actually installed so the next paint re-renders from it.
Mike-Solar
a97bc19c14