05/06 Fix some notable and quality issues

app/routes/scheduled_reports.py

@@ -50,13 +50,20 @@ bp = Blueprint('scheduled_reports', __name__, url_prefix='/scheduled-reports')
 # ── Helpers ───────────────────────────────────────────────────────────────────
 
 def _compute_next_send(frequency: str, from_dt: datetime = None) -> datetime:
-    """Return the next send datetime for a given frequency."""
+    """Return the next send datetime for a given frequency.
+
+    Monthly cadence always targets the 1st of the next month at 07:00.
+    The December branch is required because datetime.replace(month=13)
+    raises ValueError — incrementing the month directly is not safe in
+    general, but targeting day=1 avoids the separate last-day-of-month
+    (28/29/30/31) edge case that would affect mid-month scheduling.
+    """
     now = from_dt or now_eastern()
     if frequency == 'daily':
         return (now + timedelta(days=1)).replace(hour=7, minute=0, second=0, microsecond=0)
     if frequency == 'weekly':
         return (now + timedelta(weeks=1)).replace(hour=7, minute=0, second=0, microsecond=0)
-    # monthly: first of next month
+    # monthly: first of next month — December rolls over to Jan of next year.
     if now.month == 12:
         return now.replace(year=now.year + 1, month=1, day=1, hour=7, minute=0, second=0, microsecond=0)
     return now.replace(month=now.month + 1, day=1, hour=7, minute=0, second=0, microsecond=0)