fix: restore Mailu SQLite database in place

restore_sqlite.py

@@ -0,0 +1,22 @@
+#!/usr/bin/env python3
+"""Restore Mailu's SQLite snapshot without replacing the live database inode."""
+
+import sqlite3
+from pathlib import Path
+
+backup_path = Path("/data/backup/main.db")
+live_path = Path("/data/main.db")
+
+# The source and destination must already exist. A missing snapshot or live
+# database is a restore failure, not a reason to create an empty database.
+with sqlite3.connect(
+    f"{backup_path.as_uri()}?mode=ro", uri=True, timeout=60
+) as source:
+    if source.execute("PRAGMA integrity_check").fetchall() != [("ok",)]:
+        raise RuntimeError(f"Invalid SQLite snapshot: {backup_path}")
+    with sqlite3.connect(
+        f"{live_path.as_uri()}?mode=rw", uri=True, timeout=60
+    ) as destination:
+        source.backup(destination, pages=256, sleep=0.1)
+
+print(f"SQLite restore complete: {live_path}", flush=True)