test(mcp): migrate _kg monkeypatches to _get_kg (#1136)

Direct module-attribute patching of _kg is obsolete after the lazy
cache refactor. Switch test helpers to patch _get_kg instead so the
fixture KG replaces the factory rather than a now-missing singleton.

- tests/test_mcp_server.py: _patch_mcp_server helper
- tests/benchmarks/test_mcp_bench.py: _patch_mcp_config helper
- tests/benchmarks/test_memory_profile.py: inline patch in test_tool_status_repeated_calls

tests/benchmarks/test_mcp_bench.py

@@ -40,8 +40,9 @@ def _patch_mcp_config(monkeypatch, palace_path, tmp_path):
 
     import mempalace.mcp_server as mcp_mod
 
+    kg = KnowledgeGraph(db_path=str(tmp_path / "kg.sqlite3"))
     monkeypatch.setattr(mcp_mod, "_config", cfg)
-    monkeypatch.setattr(mcp_mod, "_kg", KnowledgeGraph(db_path=str(tmp_path / "kg.sqlite3")))
+    monkeypatch.setattr(mcp_mod, "_get_kg", lambda: kg)
 
 
 def _get_rss_mb():

tests/benchmarks/test_memory_profile.py

@@ -84,8 +84,9 @@ class TestToolStatusMemoryProfile:
 
         cfg = MempalaceConfig(config_dir=str(tmp_path / "cfg"))
         monkeypatch.setattr(cfg, "_file_config", {"palace_path": palace_path})
+        kg = KnowledgeGraph(db_path=str(tmp_path / "kg.sqlite3"))
         monkeypatch.setattr(mcp_mod, "_config", cfg)
-        monkeypatch.setattr(mcp_mod, "_kg", KnowledgeGraph(db_path=str(tmp_path / "kg.sqlite3")))
+        monkeypatch.setattr(mcp_mod, "_get_kg", lambda: kg)
 
         from mempalace.mcp_server import tool_status
 

tests/test_mcp_server.py

@@ -18,7 +18,7 @@ def _patch_mcp_server(monkeypatch, config, kg):
     from mempalace import mcp_server
 
     monkeypatch.setattr(mcp_server, "_config", config)
-    monkeypatch.setattr(mcp_server, "_kg", kg)
+    monkeypatch.setattr(mcp_server, "_get_kg", lambda: kg)
 
 
 def _get_collection(palace_path, create=False):