Bound paged retrieval responses

tests/test_core.py

@@ -378,6 +378,27 @@ class DocForgeCoreTests(unittest.TestCase):
                     operation()
                 self.assertEqual("invalid_limit", invalid.exception.code)
 
+    def test_incoming_traversal_uses_source_ordered_covering_index(self) -> None:
+        with tempfile.TemporaryDirectory() as directory:
+            root = self.copy_fixture("alpha", Path(directory))
+            index = ProjectIndex(Project.open(root))
+            index.build()
+
+            connection = sqlite3.connect(index.path)
+            try:
+                plan = connection.execute(
+                    "EXPLAIN QUERY PLAN "
+                    "SELECT source_id, relation, target_id FROM edges "
+                    "WHERE target_id = ? "
+                    "ORDER BY source_id, relation, target_id LIMIT ?",
+                    ("guide.foundation", 101),
+                ).fetchall()
+            finally:
+                connection.close()
+            details = " ".join(str(row[3]) for row in plan)
+            self.assertIn("edges_target_source", details)
+            self.assertNotIn("USE TEMP B-TREE", details)
+
     def test_query_rechecks_source_identity_before_returning(self) -> None:
         with tempfile.TemporaryDirectory() as directory:
             root = self.copy_fixture("alpha", Path(directory))