fix: prune old detail after publication (#100)

tests/test_repair.py

@@ -235,8 +235,8 @@ class TestBoundaryAnchorRetention:
         # the interval spans the retention boundary
         assert needs_boundary_anchor(store_conn, "2026-09-15T23:55:00+00:00", now)
 
-    def test_not_boundary_anchor_if_fully_derived(self, store_conn):
-        """Sample that's fully derived is not a boundary anchor."""
+    def test_hour_only_derivation_does_not_replace_local_day_evidence(self, store_conn):
+        """UTC hour evidence alone does not make a sample safe to prune."""
         now = datetime(2026, 9, 30, 12, 0, 0, tzinfo=timezone.utc)
         
         # Insert sample and fully derive its interval
@@ -247,8 +247,7 @@ class TestBoundaryAnchorRetention:
         _insert_hour(store_conn, "2026-09-14T10:00:00+00:00", 
                      bytes_written_delta=1000000)
         
-        # Not a boundary anchor
-        assert not needs_boundary_anchor(store_conn, "2026-09-14T10:00:00+00:00", now)
+        assert needs_boundary_anchor(store_conn, "2026-09-14T10:00:00+00:00", now)
 
     def test_pruning_retains_boundary_anchors(self, store_conn):
         """Pruning keeps samples needed as boundary anchors."""
@@ -274,8 +273,8 @@ class TestBoundaryAnchorRetention:
         )
         assert cursor.fetchone()[0] == 1
 
-    def test_pruning_removes_old_sample_with_derived_interval(self, store_conn):
-        """Pruning removes old samples when interval is fully derived."""
+    def test_pruning_keeps_samples_without_local_day_replacement(self, store_conn):
+        """Pruning keeps samples when only the UTC-hour row exists."""
         now = datetime(2026, 9, 30, 12, 0, 0, tzinfo=timezone.utc)
         
         # Old sample with derived interval
@@ -289,11 +288,11 @@ class TestBoundaryAnchorRetention:
         # Run pruning
         pruned = prune_old_samples(store_conn, now, retention_days=14)
         
-        # Old sample should be removed (interval is derived)
+        # The source remains until local-day evidence is also durable.
         cursor = store_conn.execute(
             "SELECT COUNT(*) FROM samples WHERE ts = '2026-09-10T10:00:00+00:00'"
         )
-        assert cursor.fetchone()[0] == 0
+        assert cursor.fetchone()[0] == 1
 
 
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