fix: guard local-day pruning across monitoring gaps (#100)

src/fenris/pruning.py

@@ -143,6 +143,24 @@ def _contains_instant(
     return bounds is not None and bounds[0] <= instant < bounds[1]
 
 
+def _monitoring_period_covers(
+    conn: sqlite3.Connection,
+    start: datetime,
+    end: datetime,
+) -> bool:
+    """Require continuous monitoring before a local-day total replaces detail."""
+    for started_at, ended_at in conn.execute(
+        "SELECT started_at, ended_at FROM monitoring_periods"
+    ):
+        period_start = _parse_sample_time(started_at)
+        period_end = _parse_sample_time(ended_at) if ended_at is not None else None
+        if period_start is None or period_start > start:
+            continue
+        if ended_at is None or (period_end is not None and end <= period_end):
+            return True
+    return False
+
+
 def _has_local_replacement(
     conn: sqlite3.Connection,
     previous: tuple,
@@ -157,7 +175,12 @@ def _has_local_replacement(
 
     start_id, end_id = previous[0], current[0]
     segment_id = current[2]
-    if start_tz and start_tz == end_tz and segment_id is not None:
+    if (
+        start_tz
+        and start_tz == end_tz
+        and segment_id is not None
+        and _monitoring_period_covers(conn, start, end)
+    ):
         known_days = conn.execute(
             "SELECT local_days.utc_start, local_days.utc_end "
             "FROM local_days JOIN local_day_segment_totals "