feat(question_gen): register ActionRecognitionStrategy, replace temp VISUAL binding

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app/question_gen/strategy.py

@@ -104,7 +104,7 @@ class TaskTypeStrategy(Protocol):
 
 # 消歧绑定表：多归属题型确定性绑定到一个 family
 _TASK_TYPE_TO_FAMILY: dict[str, QuestionFamilySpec] = {
-    "Action Recognition": VISUAL_FAMILY,  # Plan A 临时绑定；Plan B 替换为特化策略
+    "Action Recognition": VISUAL_FAMILY,  # fallback — 注册表中已被 ActionRecognitionStrategy 替换
     "Object Recognition": RETRIEVAL_FAMILY,
     "Object Reasoning": REASONING_FAMILY,
     "Action Reasoning": REASONING_FAMILY,
@@ -200,9 +200,14 @@ def register_strategy(strategy: TaskTypeStrategy) -> None:
     _STRATEGY_REGISTRY[strategy.task_type] = strategy
 
 
+_BUILTIN_REGISTERED = False
+
+
 def get_strategy(task_type: str) -> TaskTypeStrategy:
     """获取题型策略。未注册的自动创建 BaseTaskTypeStrategy。
 
+    首次调用时延迟注册内建特化策略（避免循环导入）。
+
     参数:
         task_type: 题型名。
 
@@ -212,6 +217,11 @@ def get_strategy(task_type: str) -> TaskTypeStrategy:
     异常:
         KeyError: task_type 不在消歧绑定表和注册表中。
     """
+    global _BUILTIN_REGISTERED  # noqa: PLW0603
+    if not _BUILTIN_REGISTERED:
+        _BUILTIN_REGISTERED = True
+        _register_builtin_strategies()
+
     if task_type in _STRATEGY_REGISTRY:
         return _STRATEGY_REGISTRY[task_type]
     return _build_default_strategy(task_type)
@@ -231,3 +241,10 @@ def _build_default_strategy(task_type: str) -> BaseTaskTypeStrategy:
     """
     family = _TASK_TYPE_TO_FAMILY[task_type]
     return BaseTaskTypeStrategy(task_type=task_type, family=family)
+
+
+def _register_builtin_strategies() -> None:
+    """注册内建的特化策略。由 get_strategy 首次调用时延迟执行。"""
+    from app.question_gen.strategy_action_recognition import ActionRecognitionStrategy
+
+    register_strategy(ActionRecognitionStrategy())

tests/unit/test_strategy.py

@@ -116,3 +116,27 @@ class TestSubPattern:
         )
         with pytest.raises(AttributeError):
             sp.name = "changed"
+
+
+class TestActionRecognitionRegistration:
+    """AR 策略注册后 get_strategy 返回特化实例。"""
+
+    def test_get_strategy_returns_ar_strategy(self):
+        """get_strategy('Action Recognition') 返回 ActionRecognitionStrategy。"""
+        from app.question_gen.strategy_action_recognition import ActionRecognitionStrategy
+
+        s = get_strategy("Action Recognition")
+        assert isinstance(s, ActionRecognitionStrategy)
+        assert s.task_type == "Action Recognition"
+        assert s.strategy_name == "ACTION_RECOGNITION"
+
+    def test_ar_not_base_strategy(self):
+        """get_strategy('Action Recognition') 不再返回 BaseTaskTypeStrategy。"""
+        s = get_strategy("Action Recognition")
+        assert not isinstance(s, BaseTaskTypeStrategy)
+
+    def test_other_types_still_base(self):
+        """其他题型仍返回 BaseTaskTypeStrategy。"""
+        for tt in ("Object Recognition", "Temporal Reasoning", "Spatial Reasoning"):
+            s = get_strategy(tt)
+            assert isinstance(s, BaseTaskTypeStrategy), f"{tt} 应该是 BaseTaskTypeStrategy"