Fixed
- The transcript sweeper no longer errors when two sweeps run concurrently on
the same session._write_sweep_statenow writes to a unique per-process
temp file, so runningtranscript-sweep runback to back no longer races on
a shared temp path and raises a spuriousFileNotFoundError(surfaced as
files_failed). No data was lost — content is staged before the state write —
but the errors were alarming on a first run. (#165)