Automatic subtree watching only reacted to `CREATE`, so a directory
moved in from elsewhere stayed unwatched. It is now handled like a
created one. Items that already exist in such a directory never
produce kernel events; they are reported with the same event kind
and `synthesized` set to `true`, so consumers can treat them as
newly appeared.
`IN_Q_OVERFLOW` arrives with watch descriptor -1, so the path lookup
failed and the event was silently discarded. It is now delivered
with an empty path so consumers can rescan after the kernel dropped
events.