diff --git a/app/question_gen/families.py b/app/question_gen/families.py
new file mode 100644
index 0000000..a8c3c1a
--- /dev/null
+++ b/app/question_gen/families.py
@@ -0,0 +1,263 @@
+"""题族规格声明 — 定义 5 大问题家族及其采样、泄漏检测、提示模板约束。
+
+每个 QuestionFamilySpec 对应一种失败机制（skill_target M1–M5），
+由 get_family_for_slot 在出题时按权重分配。
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    import random
+
+
+@dataclass(frozen=True)
+class LeakTestProfile:
+    """泄漏测试配置 — 定义快捷答题捷径类型与通过阈值。
+
+    Attributes:
+        shortcut_type: 捷径类型标识。
+        probe_template: store/prompts/question_gen/ 下的探测模板文件名。
+        pass_threshold: 通过阈值（0–1），低于此值视为存在泄漏。
+    """
+
+    shortcut_type: str
+    probe_template: str
+    pass_threshold: float
+
+
+@dataclass(frozen=True)
+class SamplingConstraint:
+    """采样约束 — 对树节点的最低要求。
+
+    Attributes:
+        min_subtitles: 最少字幕段数。
+        min_l3_nodes: 最少 L3 节点数。
+        require_frames: 是否要求帧图像可用。
+        cross_l2_span: 是否要求跨 L2 段采样。
+    """
+
+    min_subtitles: int
+    min_l3_nodes: int
+    require_frames: bool
+    cross_l2_span: bool
+
+
+@dataclass(frozen=True)
+class QuestionFamilySpec:
+    """问题家族规格 — 一个家族的完整声明。
+
+    Attributes:
+        name: 家族标识名（如 "RETRIEVAL"）。
+        skill_target: 目标失败机制编号（M1–M5）。
+        sampling: 采样约束。
+        legal_task_types: 该家族合法的任务类型集合（frozenset）。
+        leak_profile: 泄漏测试配置。
+        prompt_template: 出题 prompt 模板文件名。
+    """
+
+    name: str
+    skill_target: str
+    sampling: SamplingConstraint
+    legal_task_types: frozenset[str]
+    leak_profile: LeakTestProfile
+    prompt_template: str
+
+
+# ---------------------------------------------------------------------------
+# 5 大家族实例
+# ---------------------------------------------------------------------------
+
+RETRIEVAL_FAMILY = QuestionFamilySpec(
+    name="RETRIEVAL",
+    skill_target="M1",
+    sampling=SamplingConstraint(
+        min_subtitles=2,
+        min_l3_nodes=3,
+        require_frames=False,
+        cross_l2_span=False,
+    ),
+    legal_task_types=frozenset(
+        [
+            "Action Recognition",
+            "Action Reasoning",
+            "Action Prediction",
+            "Action Sequence",
+            "Object Recognition",
+            "Object Reasoning",
+            "Object Interaction",
+            "Scene Understanding",
+            "Event Reasoning",
+            "Causal Reasoning",
+            "Temporal Reasoning",
+            "Spatial Reasoning",
+        ]
+    ),
+    leak_profile=LeakTestProfile(
+        shortcut_type="temporal_proximity",
+        probe_template="gate_leak_retrieval.md",
+        pass_threshold=0.6,
+    ),
+    prompt_template="retrieval.md",
+)
+
+REASONING_FAMILY = QuestionFamilySpec(
+    name="REASONING",
+    skill_target="M2",
+    sampling=SamplingConstraint(
+        min_subtitles=3,
+        min_l3_nodes=4,
+        require_frames=False,
+        cross_l2_span=True,
+    ),
+    legal_task_types=frozenset(
+        [
+            "Action Reasoning",
+            "Object Reasoning",
+            "Event Reasoning",
+            "Causal Reasoning",
+            "Temporal Reasoning",
+            "Spatial Reasoning",
+        ]
+    ),
+    leak_profile=LeakTestProfile(
+        shortcut_type="frequency",
+        probe_template="gate_leak_reasoning.md",
+        pass_threshold=0.5,
+    ),
+    prompt_template="reasoning.md",
+)
+
+ENUMERATION_FAMILY = QuestionFamilySpec(
+    name="ENUMERATION",
+    skill_target="M3",
+    sampling=SamplingConstraint(
+        min_subtitles=2,
+        min_l3_nodes=5,
+        require_frames=False,
+        cross_l2_span=False,
+    ),
+    legal_task_types=frozenset(
+        [
+            "Action Sequence",
+            "Object Recognition",
+            "Object Interaction",
+            "Scene Understanding",
+        ]
+    ),
+    leak_profile=LeakTestProfile(
+        shortcut_type="option_length",
+        probe_template="gate_leak_enumeration.md",
+        pass_threshold=0.6,
+    ),
+    prompt_template="enumeration.md",
+)
+
+VISUAL_FAMILY = QuestionFamilySpec(
+    name="VISUAL",
+    skill_target="M4",
+    sampling=SamplingConstraint(
+        min_subtitles=0,
+        min_l3_nodes=3,
+        require_frames=True,
+        cross_l2_span=False,
+    ),
+    legal_task_types=frozenset(
+        [
+            "Object Recognition",
+            "Scene Understanding",
+            "Action Recognition",
+            "Spatial Reasoning",
+        ]
+    ),
+    leak_profile=LeakTestProfile(
+        shortcut_type="visual_salience",
+        probe_template="gate_leak_visual.md",
+        pass_threshold=0.5,
+    ),
+    prompt_template="visual.md",
+)
+
+SPATIAL_FAMILY = QuestionFamilySpec(
+    name="SPATIAL",
+    skill_target="M5",
+    sampling=SamplingConstraint(
+        min_subtitles=0,
+        min_l3_nodes=3,
+        require_frames=True,
+        cross_l2_span=False,
+    ),
+    legal_task_types=frozenset(
+        [
+            "Spatial Reasoning",
+            "Object Interaction",
+            "Scene Understanding",
+        ]
+    ),
+    leak_profile=LeakTestProfile(
+        shortcut_type="spatial_default",
+        probe_template="gate_leak_spatial.md",
+        pass_threshold=0.5,
+    ),
+    prompt_template="spatial.md",
+)
+
+ALL_FAMILIES: tuple[QuestionFamilySpec, ...] = (
+    RETRIEVAL_FAMILY,
+    REASONING_FAMILY,
+    ENUMERATION_FAMILY,
+    VISUAL_FAMILY,
+    SPATIAL_FAMILY,
+)
+
+# 按 name 索引，用于 get_family_for_slot 快速查找
+_FAMILY_BY_NAME: dict[str, QuestionFamilySpec] = {f.name: f for f in ALL_FAMILIES}
+
+
+def get_family_for_slot(
+    task_type: str,
+    family_ratios: dict[str, float],
+    rng: random.Random,
+) -> QuestionFamilySpec:
+    """根据任务类型和家族权重比例，随机选择一个合法的问题家族。
+
+    Args:
+        task_type: 任务类型字符串（必须是 12 种合法类型之一）。
+        family_ratios: 家族名称到权重的映射（如 {"RETRIEVAL": 0.30, ...}）。
+        rng: 随机数生成器实例（确保可复现）。
+
+    Returns:
+        被选中的 QuestionFamilySpec。
+
+    Raises:
+        ValueError: task_type 不在任何家族的 legal_task_types 中。
+        ValueError: 给定 task_type 下没有合法家族（所有合法族权重为 0 或不在 ratios 中）。
+    """
+    # 检查 task_type 是否被任一家族接受
+    all_legal_types: set[str] = set()
+    for family in ALL_FAMILIES:
+        all_legal_types.update(family.legal_task_types)
+    if task_type not in all_legal_types:
+        msg = f"task_type '{task_type}' 不在任何家族的合法类型中"
+        raise ValueError(msg)
+
+    # 过滤出接受该 task_type 且在 ratios 中有正权重的家族
+    candidates: list[QuestionFamilySpec] = []
+    weights: list[float] = []
+    for family_name, weight in family_ratios.items():
+        family = _FAMILY_BY_NAME.get(family_name)
+        if family is None:
+            continue
+        if task_type in family.legal_task_types and weight > 0:
+            candidates.append(family)
+            weights.append(weight)
+
+    if not candidates:
+        msg = f"task_type '{task_type}' 下没有合法家族可选（检查 family_ratios）"
+        raise ValueError(msg)
+
+    # 归一化权重 + 加权随机选择
+    chosen = rng.choices(candidates, weights=weights, k=1)[0]
+    return chosen
diff --git a/tests/unit/test_families.py b/tests/unit/test_families.py
new file mode 100644
index 0000000..3f62c8c
--- /dev/null
+++ b/tests/unit/test_families.py
@@ -0,0 +1,173 @@
+"""题族规格声明单元测试。"""
+
+from __future__ import annotations
+
+import random
+from collections import Counter
+
+import pytest
+from scipy import stats
+
+from app.question_gen.families import (
+    ALL_FAMILIES,
+    RETRIEVAL_FAMILY,
+    get_family_for_slot,
+)
+
+# 12 种任务类型（来自 harness config）
+ALL_TASK_TYPES: frozenset[str] = frozenset(
+    [
+        "Action Recognition",
+        "Action Reasoning",
+        "Action Prediction",
+        "Action Sequence",
+        "Object Recognition",
+        "Object Reasoning",
+        "Object Interaction",
+        "Scene Understanding",
+        "Event Reasoning",
+        "Causal Reasoning",
+        "Temporal Reasoning",
+        "Spatial Reasoning",
+    ]
+)
+
+
+class TestFamilySpec:
+    """验证 QuestionFamilySpec 声明的完整性与一致性。"""
+
+    def test_all_families_cover_all_task_types(self) -> None:
+        """12 种任务类型在 ALL_FAMILIES 中全覆盖。"""
+        covered: set[str] = set()
+        for family in ALL_FAMILIES:
+            covered.update(family.legal_task_types)
+        assert covered == ALL_TASK_TYPES
+
+    def test_skill_targets_unique(self) -> None:
+        """每个 family 的 skill_target 不重复。"""
+        targets = [f.skill_target for f in ALL_FAMILIES]
+        assert len(targets) == len(set(targets))
+
+    def test_all_families_tuple_length(self) -> None:
+        """ALL_FAMILIES 包含 5 个家族。"""
+        assert len(ALL_FAMILIES) == 5
+
+    def test_family_instances_are_frozen(self) -> None:
+        """Family spec 实例不可修改。"""
+        with pytest.raises(AttributeError):
+            RETRIEVAL_FAMILY.name = "hacked"  # type: ignore[misc]
+
+    def test_legal_task_types_are_frozensets(self) -> None:
+        """legal_task_types 是 frozenset，确保不可变。"""
+        for family in ALL_FAMILIES:
+            assert isinstance(family.legal_task_types, frozenset)
+
+    def test_sampling_constraints_reasonable(self) -> None:
+        """采样约束值在合理范围。"""
+        for family in ALL_FAMILIES:
+            assert family.sampling.min_subtitles >= 0
+            assert family.sampling.min_l3_nodes >= 1
+
+    def test_leak_profile_thresholds_valid(self) -> None:
+        """泄漏测试阈值在 (0, 1] 范围内。"""
+        for family in ALL_FAMILIES:
+            assert 0 < family.leak_profile.pass_threshold <= 1.0
+
+    def test_prompt_templates_not_empty(self) -> None:
+        """每个 family 的 prompt_template 非空。"""
+        for family in ALL_FAMILIES:
+            assert family.prompt_template
+            assert family.prompt_template.endswith(".md")
+
+
+class TestGetFamilyForSlot:
+    """验证 get_family_for_slot 的核心行为。"""
+
+    def test_respects_legal_task_types(self) -> None:
+        """返回的 family 必须包含给定 task_type。"""
+        rng = random.Random(42)
+        for task_type in ALL_TASK_TYPES:
+            for _ in range(50):
+                family = get_family_for_slot(
+                    task_type=task_type,
+                    family_ratios={
+                        "RETRIEVAL": 0.30,
+                        "REASONING": 0.25,
+                        "ENUMERATION": 0.20,
+                        "VISUAL": 0.15,
+                        "SPATIAL": 0.10,
+                    },
+                    rng=rng,
+                )
+                assert task_type in family.legal_task_types
+
+    def test_deterministic_with_seed(self) -> None:
+        """相同 seed 产出相同结果。"""
+        ratios = {
+            "RETRIEVAL": 0.30,
+            "REASONING": 0.25,
+            "ENUMERATION": 0.20,
+            "VISUAL": 0.15,
+            "SPATIAL": 0.10,
+        }
+        results_a = []
+        results_b = []
+        for seed in range(10):
+            rng_a = random.Random(seed)
+            rng_b = random.Random(seed)
+            results_a.append(get_family_for_slot("Action Reasoning", ratios, rng_a).name)
+            results_b.append(get_family_for_slot("Action Reasoning", ratios, rng_b).name)
+        assert results_a == results_b
+
+    def test_invalid_task_type_raises(self) -> None:
+        """不存在的 task_type 抛 ValueError。"""
+        rng = random.Random(0)
+        with pytest.raises(ValueError, match="task_type"):
+            get_family_for_slot(
+                task_type="Nonexistent Type",
+                family_ratios={"RETRIEVAL": 1.0},
+                rng=rng,
+            )
+
+    def test_distribution_approximates_ratios(self) -> None:
+        """大样本下分布近似指定比例（chi-square p > 0.01）。
+
+        使用 Action Recognition — 只有 RETRIEVAL 和 VISUAL 合法。
+        """
+        rng = random.Random(123)
+        ratios = {
+            "RETRIEVAL": 0.30,
+            "REASONING": 0.25,
+            "ENUMERATION": 0.20,
+            "VISUAL": 0.15,
+            "SPATIAL": 0.10,
+        }
+        n = 5000
+        counter: Counter[str] = Counter()
+        for _ in range(n):
+            family = get_family_for_slot("Action Recognition", ratios, rng)
+            counter[family.name] += 1
+
+        # Action Recognition 合法族: RETRIEVAL(0.30), VISUAL(0.15)
+        # 归一化后: RETRIEVAL=0.30/0.45≈0.667, VISUAL=0.15/0.45≈0.333
+        legal_ratios = {"RETRIEVAL": 0.30, "VISUAL": 0.15}
+        total_weight = sum(legal_ratios.values())
+        expected_probs = {k: v / total_weight for k, v in legal_ratios.items()}
+
+        observed = [counter.get("RETRIEVAL", 0), counter.get("VISUAL", 0)]
+        expected = [expected_probs["RETRIEVAL"] * n, expected_probs["VISUAL"] * n]
+
+        chi2, p_value = stats.chisquare(observed, expected)
+        assert p_value > 0.01, f"分布偏离过大: chi2={chi2:.2f}, p={p_value:.4f}"
+
+    def test_no_legal_family_raises(self) -> None:
+        """所有 family 权重为 0 时合法族为空，应抛出 ValueError。"""
+        rng = random.Random(0)
+        # Spatial Reasoning 合法族: RETRIEVAL, REASONING, VISUAL, SPATIAL
+        # 如果 ratios 中只含不合法的族名，应抛错
+        with pytest.raises(ValueError, match="合法"):
+            get_family_for_slot(
+                task_type="Spatial Reasoning",
+                family_ratios={"ENUMERATION": 1.0},
+                rng=rng,
+            )