A classified event (chokidar).
The source finished its initial set for root.
One whole parcel batch for a root, sorted by path (D149).
The source re-created root's subscription after an error (D131).
root is reachable again (D109).
root became unreachable (D109), or is reachable but cannot be
watched (reachable, D156: it is still reconciled); code is the
error code.
Where a change source delivers events and signals. Implemented by
FileSystemWatcher, which owns classification, stability waits, pairing, renewals and every reconcile trigger (D120).