Add result extension point and migrate repeat handling

Let extensions normalize or consume each completed model result before default history and tool processing. Move repeat detection into loop control and add a dedicated empty-response warning so one turn produces one UI warning.

tests/test_message_loop_result.py

@@ -0,0 +1,63 @@
+from types import SimpleNamespace
+
+from extensions.python.message_loop_result._20_loop_control import LoopControl
+
+
+class FakeAgent:
+    def __init__(self, response: str, reasoning: str = "", last_response: str = ""):
+        self.loop_data = SimpleNamespace(
+            last_response=last_response,
+            params_temporary={},
+        )
+        self.context = SimpleNamespace(log=SimpleNamespace(log=lambda **kwargs: None))
+        self.response = response
+        self.reasoning = reasoning
+        self.warnings = []
+        self.history = []
+
+    def read_prompt(self, name):
+        return {
+            "fw.msg_empty_response.md": "empty",
+            "fw.msg_repeat.md": "repeat",
+        }[name]
+
+    def hist_add_ai_response(self, response, **kwargs):
+        self.history.append(response)
+        return SimpleNamespace(id="assistant")
+
+    def _remember_llm_result_state(self, *args):
+        pass
+
+    def hist_add_warning(self, message):
+        self.warnings.append(message)
+        return SimpleNamespace(id="warning")
+
+
+def _run(agent):
+    result_data = {
+        "llm_result": SimpleNamespace(response=agent.response, reasoning=agent.reasoning)
+    }
+    LoopControl(agent).execute(result_data)
+    return result_data
+
+
+def test_empty_result_skips_default_processing():
+    agent = FakeAgent("")
+
+    assert _run(agent)["skip_default_processing"] is True
+    assert agent.history == [""]
+    assert agent.warnings == ["empty"]
+
+
+def test_repeat_skips_default_processing():
+    agent = FakeAgent('{"tool_name":"response"}', last_response='{"tool_name":"response"}')
+
+    assert _run(agent)["skip_default_processing"] is True
+    assert agent.warnings == ["repeat"]
+
+
+def test_result_with_reasoning_uses_default_processing():
+    agent = FakeAgent("", reasoning="thinking")
+
+    assert "skip_default_processing" not in _run(agent)
+    assert agent.history == []