Harden local runtime safety and error handling

bible-local/06-backup.md

@@ -5,8 +5,7 @@
 Automatic rotating ZIP backup system for local data.
 
 **What is included in each archive:**
-- SQLite DB (`qfs.db`)
-- SQLite sidecars (`qfs.db-wal`, `qfs.db-shm`) if present
+- Consistent SQLite snapshot stored as `qfs.db`
 - `config.yaml` if present
 
 **Archive name format:** `qfs-backp-YYYY-MM-DD.zip`
@@ -78,6 +77,7 @@ type BackupConfig struct {
 ## Implementation Notes
 
 - `backup.time` is in **local time** without timezone offset parsing
+- Backup captures a consistent SQLite snapshot via `VACUUM INTO` before zipping; it does not archive live `-wal` / `-shm` sidecars directly
 - `.period.json` is the marker that prevents duplicate backups within the same period
 - Archive filenames contain only the date; uniqueness is ensured by per-period directories + the period marker
 - When changing naming or retention: update both the filename logic and the prune logic together