US07-04: Prove Concurrency and Crash Recovery (#86)

photo_pipeline/services/rename_journal.py

@@ -81,7 +81,17 @@ ALLOWED_TRANSITIONS = {
 
 TERMINAL_STATES = frozenset({JournalState.COMPLETE, JournalState.ROLLED_BACK})
 # States where the disk may already have been touched by this operation.
-UNSAFE_STATES = frozenset({JournalState.MOVING, JournalState.MOVED, JournalState.DATABASE_UPDATED})
+# ``rollback_required`` belongs here too (US07-04): the move happened and someone
+# has to decide what to do about it, so the library is not in a state another
+# mutation may build on.
+UNSAFE_STATES = frozenset(
+    {
+        JournalState.MOVING,
+        JournalState.MOVED,
+        JournalState.DATABASE_UPDATED,
+        JournalState.ROLLBACK_REQUIRED,
+    }
+)
 
 RESUMABLE = "resumable"
 ROLLBACK_SAFE = "rollback_safe"