fix(tests): set num_threads=1 on Kuzu Connection to avoid asyncio conflicts

The segfault was caused by pytest-asyncio's background event loop thread
conflicting with Kuzu's internal threading. Setting num_threads=1 on
Connection initialization avoids this conflict.

Changes:
- KuzuGraph.__init__: Set num_threads=1 on Connection
- conftest kuzu_db_path fixture: Set num_threads=1
- test_kuzu_queries helper: Set num_threads=1

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: HumanBean17

kuzu_queries.py

@@ -337,7 +337,8 @@ class KuzuGraph:
     def __init__(self, db_path: str) -> None:
         self.db_path = db_path
         self._db = kuzu.Database(db_path, read_only=True)
-        self._conn = kuzu.Connection(self._db)
+        # num_threads=1 avoids internal threading that conflicts with pytest-asyncio
+        self._conn = kuzu.Connection(self._db, num_threads=1)
         self._conn_lock = threading.Lock()
 
     def close(self) -> None:

tests/conftest.py

@@ -61,7 +61,7 @@ def kuzu_db_path(tmp_path_factory, corpus_root: Path) -> Path:
     build_kuzu_to(corpus_root, db_path, max_pass=5)
 
     db = kuzu.Database(str(db_path), read_only=True)
-    conn = kuzu.Connection(db)
+    conn = kuzu.Connection(db, num_threads=1)
     n_types = 0
     r = conn.execute("MATCH (s:Symbol) WHERE s.kind = 'class' RETURN count(*) AS n")
     if r.has_next():

tests/test_kuzu_queries.py

@@ -376,7 +376,7 @@ def test_trace_flow_empty_seeds_returns_empty(kuzu_graph) -> None:
 def _open_stale_ontology_graph(tmp_path: Path, ontology_version: int) -> Path:
     db_path = tmp_path / f"stale_ontology_{ontology_version}.kuzu"
     db = kuzu.Database(str(db_path))
-    conn = kuzu.Connection(db)
+    conn = kuzu.Connection(db, num_threads=1)
     conn.execute(
         "CREATE NODE TABLE GraphMeta("
         "key STRING PRIMARY KEY, "