fix(tests): revert num_threads=1 and aggressive Kuzu cleanup from failed fix chain

The 5 prior fix attempts introduced num_threads=1 and explicit close/GC
in conftest fixtures. These changes ALTERED Kuzu's C++ threading behavior
and likely converted a latent race condition into a reliable segfault on
CI. The original code (default num_threads, no explicit close) ran fine
alongside the LanceDB background thread for months.

The real fix is preventing the LanceDB thread from being created (done
in prior commits). Reverting these workarounds restores the stable state.

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

Author: HumanBean17

kuzu_queries.py

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

tests/conftest.py

@@ -52,17 +52,14 @@ def _session_db_path(tmp_path_factory: pytest.TempPathFactory, name: str) -> Pat
 @pytest.fixture(scope="session")
 def kuzu_db_path(tmp_path_factory, corpus_root: Path) -> Path:
     """Bank-chat Kuzu DB: pass1–5 + ``write_kuzu`` (no pass6)."""
-    import gc
-
     import kuzu
 
     from _builders import build_kuzu_to
 
     db_path = _session_db_path(tmp_path_factory, "bank_chat")
     build_kuzu_to(corpus_root, db_path, max_pass=5)
 
-    db = kuzu.Database(str(db_path), read_only=True)
-    conn = kuzu.Connection(db, num_threads=1)
+    conn = kuzu.Connection(kuzu.Database(str(db_path), read_only=True))
     n_types = 0
     r = conn.execute("MATCH (s:Symbol) WHERE s.kind = 'class' RETURN count(*) AS n")
     if r.has_next():
@@ -71,12 +68,6 @@ def kuzu_db_path(tmp_path_factory, corpus_root: Path) -> Path:
     r = conn.execute("MATCH ()-[e:INJECTS]->() RETURN count(e) AS n")
     n_injects = int(r.get_next()[0] or 0) if r.has_next() else 0
     assert n_injects >= 1, "build produced no INJECTS edges"
-    del r
-    conn.close()
-    conn = None
-    db.close()
-    db = None
-    gc.collect()
     return db_path