Round up scheduled_at to next minute for Cronicle one-shot timing

If scheduled_at has sub-minute seconds (e.g. retry = now+30s), the
Cronicle event would fire at the start of that minute before the message
is due and find nothing. Round up so it always fires after the due time.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

utils/cronicle.py

@@ -1,6 +1,6 @@
 import logging
 import os
-from datetime import datetime, timezone
+from datetime import datetime, timedelta, timezone
 
 import httpx
 
@@ -70,6 +70,10 @@ def _build_timing(scheduled_at: datetime, recurrence: str) -> dict:
     - monthly: fires every month on the same day-of-month and hour/minute
     """
     utc = scheduled_at.astimezone(timezone.utc)
+    # Round up to the next minute if there are sub-minute seconds so Cronicle
+    # fires after the message is due, not before.
+    if utc.second or utc.microsecond:
+        utc = (utc + timedelta(minutes=1)).replace(second=0, microsecond=0)
     h, m = utc.hour, utc.minute
 
     if recurrence == "daily":