feat(v2): complete v2 reimplementation

tests/fault/test_schedule_delivery.py

@@ -0,0 +1,20 @@
+from __future__ import annotations
+
+from datetime import UTC, datetime, timedelta
+
+import pytest
+from backup_tool.scheduler import next_nominal
+
+
+def test_misfire_window_is_deterministic_for_delivery() -> None:
+    nominal = datetime.now(UTC) - timedelta(seconds=901)
+    next_run = next_nominal("* * * * *", "UTC", nominal)
+
+    assert next_run > nominal
+    assert (datetime.now(UTC) - nominal).total_seconds() > 900
+
+
+@pytest.mark.parametrize("cron", ["* * * * * *", "invalid"])
+def test_delivery_rejects_invalid_cron_before_enqueue(cron: str) -> None:
+    with pytest.raises(ValueError):
+        next_nominal(cron, "UTC")