feat(question_gen): add TaskTypeStrategy Protocol and BaseTaskTypeStrategy

- TaskTypeStrategy Protocol: pipeline 的唯一接口，定义 task_type、
  sampling_level、sampling_constraint、prompt_template 等属性
- SubPattern frozen dataclass: 出题子模式，靶向特定失败机制
- BaseTaskTypeStrategy: 封装现有 QuestionFamilySpec 行为的默认策略，
  所有属性委托给绑定的 family
- _TASK_TYPE_TO_FAMILY: 消歧绑定表，12 个题型确定性绑定到 1 个 family
- register_strategy/get_strategy: 注册表 API，未注册题型自动创建
  BaseTaskTypeStrategy
- 13 个单元测试全部通过

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

app/question_gen/strategy.py

@@ -0,0 +1,233 @@
+"""题型出题策略 — Clean Architecture 的 Strategy 层。
+
+将出题管线从 5 个粗粒度 QuestionFamilySpec 替换为 12 个题型级别的
+TaskTypeStrategy。BaseTaskTypeStrategy 封装现有 family 行为，
+特化策略（如 ActionRecognitionStrategy）自包含。
+
+典型用法::
+
+    strategy = get_strategy("Action Reasoning")
+    level = strategy.sampling_level
+    constraint = strategy.sampling_constraint
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass, field
+from typing import TYPE_CHECKING, Any, Protocol, runtime_checkable
+
+from app.question_gen.families import (
+    ENUMERATION_FAMILY,
+    REASONING_FAMILY,
+    RETRIEVAL_FAMILY,
+    SPATIAL_FAMILY,
+    VISUAL_FAMILY,
+    QuestionFamilySpec,
+    SamplingConstraint,
+)
+from app.question_gen.sampler_v2 import _TASK_TYPE_TO_LEVEL
+
+if TYPE_CHECKING:
+    import random
+
+
+# ---------------------------------------------------------------------------
+# SubPattern
+# ---------------------------------------------------------------------------
+
+
+@dataclass(frozen=True)
+class SubPattern:
+    """出题子模式 — 靶向特定失败机制。
+
+    属性:
+        name: 子模式标识名。
+        weight: 选择权重（按比例分配）。
+        sampling_level_override: 覆盖策略默认采样层级（None = 不覆盖）。
+        constraint_override: 覆盖策略默认采样约束（None = 不覆盖）。
+        instruction: 核心出题指令（1-3 句话）。
+        positive_examples: VME 原题 few-shot 示范。
+        negative_examples: 反面示例。
+        distractor_rules: 干扰项构造规则。
+    """
+
+    name: str
+    weight: float
+    sampling_level_override: int | None
+    constraint_override: SamplingConstraint | None
+    instruction: str
+    positive_examples: list[dict] = field(default_factory=list)
+    negative_examples: list[dict] = field(default_factory=list)
+    distractor_rules: str = ""
+
+
+# ---------------------------------------------------------------------------
+# Protocol
+# ---------------------------------------------------------------------------
+
+
+@runtime_checkable
+class TaskTypeStrategy(Protocol):
+    """题型出题策略 — pipeline 的唯一接口。"""
+
+    @property
+    def task_type(self) -> str: ...
+
+    @property
+    def sampling_level(self) -> int: ...
+
+    @property
+    def sampling_constraint(self) -> SamplingConstraint: ...
+
+    @property
+    def prompt_template(self) -> str: ...
+
+    @property
+    def strategy_name(self) -> str: ...
+
+    @property
+    def skill_target(self) -> str: ...
+
+    @property
+    def leak_probe_template(self) -> str: ...
+
+    def select_sub_pattern(self, rng: random.Random) -> SubPattern | None: ...
+
+    def build_prompt_context(self, material: Any, sub_pattern: SubPattern | None) -> dict: ...
+
+    def extra_gates(self, candidate: Any) -> list: ...
+
+
+# ---------------------------------------------------------------------------
+# BaseTaskTypeStrategy
+# ---------------------------------------------------------------------------
+
+# 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
+    "Object Recognition": RETRIEVAL_FAMILY,
+    "Object Reasoning": REASONING_FAMILY,
+    "Action Reasoning": REASONING_FAMILY,
+    "Attribute Perception": VISUAL_FAMILY,
+    "OCR Problems": VISUAL_FAMILY,
+    "Counting Problem": ENUMERATION_FAMILY,
+    "Information Synopsis": REASONING_FAMILY,
+    "Temporal Reasoning": ENUMERATION_FAMILY,
+    "Temporal Perception": ENUMERATION_FAMILY,
+    "Spatial Reasoning": SPATIAL_FAMILY,
+    "Spatial Perception": SPATIAL_FAMILY,
+}
+
+
+class BaseTaskTypeStrategy:
+    """封装现有 QuestionFamilySpec 行为的默认策略。
+
+    所有属性委托给绑定的 family，确保未特化题型的行为不变。
+
+    参数:
+        task_type: 题型名。
+        family: 绑定的 QuestionFamilySpec。
+    """
+
+    def __init__(self, task_type: str, family: QuestionFamilySpec) -> None:
+        self._task_type = task_type
+        self._family = family
+
+    @property
+    def task_type(self) -> str:
+        """返回题型名。"""
+        return self._task_type
+
+    @property
+    def sampling_level(self) -> int:
+        """返回采样层级（从 _TASK_TYPE_TO_LEVEL 查询）。"""
+        return _TASK_TYPE_TO_LEVEL[self._task_type]
+
+    @property
+    def sampling_constraint(self) -> SamplingConstraint:
+        """返回采样约束（委托给绑定的 family）。"""
+        return self._family.sampling
+
+    @property
+    def prompt_template(self) -> str:
+        """返回 prompt 模板文件名（委托给绑定的 family）。"""
+        return self._family.prompt_template
+
+    @property
+    def strategy_name(self) -> str:
+        """返回策略名（即 family.name）。"""
+        return self._family.name
+
+    @property
+    def skill_target(self) -> str:
+        """返回目标失败机制编号（委托给绑定的 family）。"""
+        return self._family.skill_target
+
+    @property
+    def leak_probe_template(self) -> str:
+        """返回泄漏探测模板文件名（委托给绑定的 family.leak_profile）。"""
+        return self._family.leak_profile.probe_template
+
+    def select_sub_pattern(self, rng: random.Random) -> SubPattern | None:
+        """BaseTaskTypeStrategy 无子模式。"""
+        return None
+
+    def build_prompt_context(self, material: Any, sub_pattern: SubPattern | None) -> dict:
+        """返回基础 prompt 上下文（family_name + prompt_template）。"""
+        return {
+            "family_name": self._family.name,
+            "prompt_template": self._family.prompt_template,
+        }
+
+    def extra_gates(self, candidate: Any) -> list:
+        """BaseTaskTypeStrategy 无额外 gate。"""
+        return []
+
+
+# ---------------------------------------------------------------------------
+# 注册表
+# ---------------------------------------------------------------------------
+
+_STRATEGY_REGISTRY: dict[str, TaskTypeStrategy] = {}
+
+
+def register_strategy(strategy: TaskTypeStrategy) -> None:
+    """注册一个题型策略。同一 task_type 重复注册会覆盖。
+
+    参数:
+        strategy: 实现 TaskTypeStrategy 接口的策略实例。
+    """
+    _STRATEGY_REGISTRY[strategy.task_type] = strategy
+
+
+def get_strategy(task_type: str) -> TaskTypeStrategy:
+    """获取题型策略。未注册的自动创建 BaseTaskTypeStrategy。
+
+    参数:
+        task_type: 题型名。
+
+    返回:
+        TaskTypeStrategy 实例。
+
+    异常:
+        KeyError: task_type 不在消歧绑定表和注册表中。
+    """
+    if task_type in _STRATEGY_REGISTRY:
+        return _STRATEGY_REGISTRY[task_type]
+    return _build_default_strategy(task_type)
+
+
+def _build_default_strategy(task_type: str) -> BaseTaskTypeStrategy:
+    """根据消歧绑定表自动构造 BaseTaskTypeStrategy。
+
+    参数:
+        task_type: 题型名。
+
+    返回:
+        BaseTaskTypeStrategy 实例。
+
+    异常:
+        KeyError: task_type 不在消歧绑定表中。
+    """
+    family = _TASK_TYPE_TO_FAMILY[task_type]
+    return BaseTaskTypeStrategy(task_type=task_type, family=family)

tests/unit/test_strategy.py

@@ -0,0 +1,118 @@
+"""TaskTypeStrategy Protocol 与 BaseTaskTypeStrategy 单元测试。"""
+
+from __future__ import annotations
+
+import random
+
+import pytest
+
+from app.question_gen.families import (
+    ENUMERATION_FAMILY,
+    REASONING_FAMILY,
+    RETRIEVAL_FAMILY,
+    SPATIAL_FAMILY,
+    VISUAL_FAMILY,
+)
+from app.question_gen.strategy import (
+    BaseTaskTypeStrategy,
+    SubPattern,
+    get_strategy,
+    register_strategy,
+)
+
+
+class TestBaseTaskTypeStrategy:
+    """BaseTaskTypeStrategy 封装 family 行为。"""
+
+    def test_task_type_and_strategy_name(self):
+        """task_type 和 strategy_name 正确返回。"""
+        s = BaseTaskTypeStrategy(task_type="Object Recognition", family=RETRIEVAL_FAMILY)
+        assert s.task_type == "Object Recognition"
+        assert s.strategy_name == "RETRIEVAL"
+
+    def test_sampling_from_family(self):
+        """采样参数从绑定的 family 读取。"""
+        s = BaseTaskTypeStrategy(task_type="Temporal Reasoning", family=ENUMERATION_FAMILY)
+        assert s.sampling_level == 1
+        assert s.sampling_constraint.min_l3_nodes == 5
+
+    def test_skill_target_from_family(self):
+        """skill_target 从 family 读取。"""
+        s = BaseTaskTypeStrategy(task_type="Action Reasoning", family=REASONING_FAMILY)
+        assert s.skill_target == "M2"
+
+    def test_leak_probe_template(self):
+        """leak_probe_template 从 family.leak_profile 读取。"""
+        s = BaseTaskTypeStrategy(task_type="Spatial Reasoning", family=SPATIAL_FAMILY)
+        assert s.leak_probe_template == "gate_leak_spatial.md"
+
+    def test_prompt_template_from_family(self):
+        """prompt_template 从 family 读取。"""
+        s = BaseTaskTypeStrategy(task_type="OCR Problems", family=VISUAL_FAMILY)
+        assert s.prompt_template == "visual.md"
+
+    def test_select_sub_pattern_returns_none(self):
+        """BaseTaskTypeStrategy 无子模式。"""
+        s = BaseTaskTypeStrategy(task_type="Object Recognition", family=RETRIEVAL_FAMILY)
+        rng = random.Random(42)
+        assert s.select_sub_pattern(rng) is None
+
+    def test_extra_gates_returns_empty(self):
+        """BaseTaskTypeStrategy 无额外 gate。"""
+        s = BaseTaskTypeStrategy(task_type="Object Recognition", family=RETRIEVAL_FAMILY)
+        assert s.extra_gates(None) == []
+
+
+class TestSamplingLevelMapping:
+    """BaseTaskTypeStrategy 的 sampling_level 从 _TASK_TYPE_TO_LEVEL 读取。"""
+
+    def test_l3_types(self):
+        """L3 题型。"""
+        for tt in ("Object Recognition",):
+            s = BaseTaskTypeStrategy(task_type=tt, family=RETRIEVAL_FAMILY)
+            assert s.sampling_level == 3, f"{tt} should be L3"
+
+    def test_l2_types(self):
+        """L2 题型。"""
+        s = BaseTaskTypeStrategy(task_type="Action Reasoning", family=REASONING_FAMILY)
+        assert s.sampling_level == 2
+
+    def test_l1_types(self):
+        """L1 题型。"""
+        s = BaseTaskTypeStrategy(task_type="Temporal Reasoning", family=ENUMERATION_FAMILY)
+        assert s.sampling_level == 1
+
+
+class TestStrategyRegistry:
+    """注册表查找。"""
+
+    def test_get_unregistered_returns_base(self):
+        """未注册题型返回 BaseTaskTypeStrategy。"""
+        s = get_strategy("Spatial Reasoning")
+        assert isinstance(s, BaseTaskTypeStrategy)
+        assert s.task_type == "Spatial Reasoning"
+
+    def test_register_and_get(self):
+        """注册后 get 返回注册的策略。"""
+        custom = BaseTaskTypeStrategy(task_type="Object Recognition", family=RETRIEVAL_FAMILY)
+        register_strategy(custom)
+        assert get_strategy("Object Recognition") is custom
+
+
+class TestSubPattern:
+    """SubPattern 数据类。"""
+
+    def test_frozen(self):
+        """SubPattern 不可变。"""
+        sp = SubPattern(
+            name="test",
+            weight=0.5,
+            sampling_level_override=None,
+            constraint_override=None,
+            instruction="test instruction",
+            positive_examples=[],
+            negative_examples=[],
+            distractor_rules="",
+        )
+        with pytest.raises(AttributeError):
+            sp.name = "changed"