fix: pace failed calendar refresh retries

backend/calendar_refresh.py

@@ -10,7 +10,7 @@ from sqlalchemy import or_, select
 from sqlalchemy.ext.asyncio import AsyncSession
 
 from . import calendar as calendar_service
-from .models import CalendarSubscription, utcnow
+from .models import CalendarSubscription
 
 logger = logging.getLogger(__name__)
 DEFAULT_REFRESH_INTERVAL = timedelta(minutes=15)
@@ -22,7 +22,9 @@ async def refresh_subscription_cache(
     row: CalendarSubscription,
     *,
     fail_without_cache: bool = True,
+    attempted_at: datetime | None = None,
 ) -> bool:
+    attempt_time = attempted_at or datetime.now(UTC)
     requested_url = row.url
     requested_version = getattr(row, "updated_at", None)
     try:
@@ -51,7 +53,8 @@ async def refresh_subscription_cache(
             row.ics_cache = result.content.decode("utf-8-sig")
             row.etag = result.etag
             row.last_modified = result.last_modified
-        row.refreshed_at = utcnow()
+        row.refreshed_at = attempt_time
+        row.updated_at = attempt_time
         row.last_error = None
         await db.commit()
         return True
@@ -61,6 +64,7 @@ async def refresh_subscription_cache(
             await db.rollback()
             raise HTTPException(502, error) from exc
         row.last_error = error
+        row.updated_at = attempt_time
         await db.commit()
         return False
 
@@ -76,13 +80,15 @@ async def refresh_due_subscriptions(
     rows = (await db.scalars(select(CalendarSubscription).where(
         CalendarSubscription.enabled.is_(True),
         or_(
-            CalendarSubscription.refreshed_at.is_(None),
-            CalendarSubscription.refreshed_at <= cutoff,
+            CalendarSubscription.updated_at.is_(None),
+            CalendarSubscription.updated_at <= cutoff,
         ),
     ).order_by(CalendarSubscription.refreshed_at, CalendarSubscription.created_at))).all()
     for row in rows:
         try:
-            await refresh_subscription_cache(db, row, fail_without_cache=False)
+            await refresh_subscription_cache(
+                db, row, fail_without_cache=False, attempted_at=current
+            )
         except Exception:
             await db.rollback()
             logger.exception("Unexpected calendar refresh failure", extra={"subscription_id": str(row.id)})