This was a mistake while adapting this code from the old state.LocalState.
Since the lock is held on the output file (s.path) the metadata should
live adjacent to that rather than being built from the read path
(s.readPath) that is used only as the initial snapshot on first
instantiation.
This also includes more logging, continuing the trend of other recent
commits in these files. The local state behavior is sufficiently complex
that these trace logs are a great help in debugging issues such as this
one with the wrong files being used or actions being taken in the wrong
order.
6cb3b0f4cf