v0.6.0: strengthen backup integrity

USERGUIDE.md

@@ -20,6 +20,8 @@ It is especially useful when you want to:
 - Keep a manifest of already-exported assets.
 - Retry transient iCloud failures.
 - Verify that files referenced by a manifest exist on disk.
+- Detect missing, zero-byte, and size-mismatched manifest files.
+- Inspect or clear deduplicated failure records.
 - Script Photos exports with stable exit codes.
 
 It is not intended to replace Apple Photos, iCloud Photos, or Time Machine. Think of it as an additional file-based export and backup tool.
@@ -339,6 +341,8 @@ Failed exports are written to:
 failures.jsonl
 ```
 
+Failure records are deduplicated by asset ID. Repeated failures update the existing record and increment the attempt count.
+
 For transient failures, first use retries during normal export:
 
 ```bash
@@ -351,6 +355,19 @@ If failures remain, retry later:
 ./bin/photoscli retry-failed --out ./PhotosBackup
 ```
 
+Clear successful retry records automatically:
+
+```bash
+./bin/photoscli retry-failed --out ./PhotosBackup --clear-on-success
+```
+
+List or clear failure records:
+
+```bash
+./bin/photoscli failures list --out ./PhotosBackup
+./bin/photoscli failures clear --out ./PhotosBackup
+```
+
 Typical reasons for failures:
 
 - iCloud asset not currently downloadable.
@@ -374,7 +391,7 @@ Run verification after large backups:
 ./bin/photoscli verify --out ./PhotosBackup --manifest sqlite
 ```
 
-Verification checks that manifest entries point to files on disk.
+Verification checks that manifest entries point to files on disk. It also reports zero-byte files and size mismatches when the manifest has a recorded size.
 
 It exits with: