v0.8.4

Changed

• Poll only the lightweight Drive revision for unchanged Google Sheets
  pairings, fetching Sheets metadata and tab values only after a local or
  remote change.
• Classify sync failures as temporary connectivity or needing attention.
  Preserve active failure and sent-email markers across service restarts,
  group changing timeout and DNS messages into the same incident, and wait at
  least 30 minutes before emailing about temporary connectivity failures.
• Include the failed spreadsheet operation, elapsed time, and available error
  code in daemon diagnostics.

Fixed

• Serialize same-file JSON writes and use collision-safe temporary filenames
  so overlapping runtime-state or pairing-index writes cannot race for the same
  temporary file and terminate the daemon.