diff --git a/needle/playground/server.py b/needle/playground/server.py
index 6525fe6..019f585 100644
--- a/needle/playground/server.py
+++ b/needle/playground/server.py
@@ -28,20 +28,19 @@ def load(self):
         self.tools_json = "[]"
 
     def complete(self, tools_json, query):
-        from .. import Needle, _lib
+        from .. import Needle
         with self.lock:
             if self.agent is None or tools_json != self.tools_json:
                 self.agent = Needle(tools=tools_json, weights=self.weights)
                 self.tools_json = tools_json
             else:
-                _lib().needle_reset()
+                self.agent.reset()
             return self.agent.complete(query)
 
     def reset(self):
-        from .. import _lib
         with self.lock:
             if self.agent is not None:
-                _lib().needle_reset()
+                self.agent.close()
             self.agent = None
             self.tools_json = None
 
diff --git a/tests/test_playground.py b/tests/test_playground.py
new file mode 100644
index 0000000..2f438bf
--- /dev/null
+++ b/tests/test_playground.py
@@ -0,0 +1,84 @@
+import pytest
+
+
+class _Agent:
+    def __init__(self, tools, weights):
+        self.tools = tools
+        self.weights = weights
+        self.calls = []
+
+    def complete(self, query, max_new_tokens=256):
+        self.calls.append(("complete", query))
+        return {"type": "text", "text": query}
+
+    def reset(self):
+        self.calls.append("reset")
+
+    def close(self):
+        self.calls.append("close")
+
+
+@pytest.fixture
+def agents(monkeypatch):
+    """Stand in for Needle, and fail the test if the global engine is touched."""
+    import needle
+
+    made = []
+
+    def build(tools=None, weights=None, **_kwargs):
+        agent = _Agent(tools, weights)
+        made.append(agent)
+        return agent
+
+    def refuse(*_args, **_kwargs):
+        raise AssertionError("the playground reached the process-global engine")
+
+    monkeypatch.setattr(needle, "Needle", build)
+    monkeypatch.setattr(needle, "_lib", refuse)
+    return made
+
+
+def test_a_second_query_on_the_same_tools_rewinds_that_agent(agents):
+    from needle.playground.server import Engine
+
+    engine = Engine()
+    engine.complete("[]", "one")
+    engine.complete("[]", "two")
+
+    assert len(agents) == 1
+    assert agents[0].calls == [("complete", "one"), "reset", ("complete", "two")]
+
+
+def test_new_tools_build_a_fresh_agent_without_rewinding(agents):
+    from needle.playground.server import Engine
+
+    engine = Engine()
+    engine.complete("[]", "one")
+    engine.complete('[{"name": "t"}]', "two")
+
+    assert len(agents) == 2
+    assert "reset" not in agents[0].calls
+    assert agents[1].calls == [("complete", "two")]
+
+
+def test_reset_closes_the_agent_it_drops(agents):
+    from needle.playground.server import Engine
+
+    engine = Engine()
+    engine.complete("[]", "one")
+    engine.reset()
+
+    assert agents[0].calls[-1] == "close"
+    assert engine.agent is None
+    assert engine.tools_json is None
+
+
+def test_a_tuned_agent_is_rewound_through_itself(agents):
+    from needle.playground.server import Engine
+
+    engine = Engine(weights="tuned.cact")
+    engine.complete("[]", "one")
+    engine.complete("[]", "two")
+
+    assert agents[0].weights == "tuned.cact"
+    assert "reset" in agents[0].calls