feat: tier-aware diag/val split with val-power repair (design 5.1)

app/harness/build_split.py

@@ -13,7 +13,7 @@ from __future__ import annotations
 
 import hashlib
 import sqlite3
-from collections import Counter
+from collections import Counter, defaultdict
 from dataclasses import asdict, dataclass, field
 from typing import TYPE_CHECKING
 
@@ -59,6 +59,8 @@ class SplitBuildConfig:
         select_seed: 贪心选择器预洗牌种子（打破等增益平局）。
         val_ratio: validation 占 trainval 视频组总数的比例。
         split_seed: 视频组题级切分的洗牌种子。
+        val_wrong_min: validation 池最少错题数，切分时保证功效（不足则从 diag 换入
+            低 T2 错题组补足，耗尽 fail-loud）。
     """
 
     n_trainval: int
@@ -68,6 +70,7 @@ class SplitBuildConfig:
     select_seed: int
     val_ratio: float
     split_seed: int
+    val_wrong_min: int
 
 
 @dataclass(frozen=True)
@@ -119,10 +122,10 @@ def build_split(
     test → 加载题库并以视频归属切三池 → 原子冻结 pools.json → 写溯源 manifest →
     六条防御断言 fail-fast 校验。
 
-    契约（Task 11，非疏漏）：build_split 有意保持 val_wrong_min-agnostic——内部调
-    split_by_video_assignment 时不传 val_wrong_min（默认 0，不校验 validation 错题
-    数）。McNemar 功效护栏是切分**冻结后**的独立校验，由 CLI 的 check_mcnemar_power
-    在 build_split 返回后执行；切分构造本身不因功效阈失败，二者关注点分离。
+    契约（Task 11）：val_wrong_min 前置到切分内保证功效——build_split 计算
+    wrong_tier_by_video 并连同 config.val_wrong_min 传入 split_by_video_assignment，
+    切分时若 val 错题不足即从 diag 换入低 T2 错题组补足（耗尽 fail-loud）。CLI 的
+    check_mcnemar_power 作切分冻结后的冗余最终确认。
 
     参数:
         db_path: harness.db 路径（只读读取 predictions，不改动）。
@@ -181,6 +184,11 @@ def build_split(
     # Phase 3: 加载题库 + 视频归属切三池 + 原子冻结。
     questions = load_benchmark(questions_dir)
     correctness = {pred["question_id"]: pred["correct"] for pred in preds}
+    tier_by_q = {row["question_id"]: row["tier"] for row in signal_rows}
+    wrong_tier_by_video: dict[str, int] = defaultdict(int)
+    for pred in preds:
+        if not pred["correct"] and tier_by_q.get(pred["question_id"]) == "T2":
+            wrong_tier_by_video[pred["video_id"]] += 1
     pools = split_by_video_assignment(
         questions,
         assignment,
@@ -188,6 +196,8 @@ def build_split(
         config.val_ratio,
         config.split_seed,
         baseline_run_id=baseline_run_id,
+        val_wrong_min=config.val_wrong_min,
+        wrong_tier_by_video=dict(wrong_tier_by_video),
     )
     save_pools(pools, out_path)
 

app/harness/pools.py

@@ -131,6 +131,7 @@ def split_by_video_assignment(
     seed: int,
     baseline_run_id: str = "",
     val_wrong_min: int = 0,
+    wrong_tier_by_video: dict[str, int] | None = None,
 ) -> Pools:
     """按视频归属做原子切分：同一视频所有题绝不跨 trainval/test 池。
 
@@ -146,7 +147,11 @@ def split_by_video_assignment(
         seed: 随机种子，保证视频组 shuffle 可复现。
         baseline_run_id: 基线 run 标识；离线切分阶段可留空，由调用方回填。
         val_wrong_min: validation 池最少错题数（默认 0 = 不检查，保持既有调用契约）。
-            > 0 时切出 val 后统计其错题数，不足即 fail loud（见 InsufficientValSignal）。
+            > 0 时切分时保证（不足则从 diag 换入低 T2 错题组补足，耗尽 fail-loud，
+            见 InsufficientValSignal）。
+        wrong_tier_by_video: video_id -> 该视频错题中 T2(defect) 数量；透传给
+            _split_trainval_by_video_group 做 tier 感知 diag/val 分配，None 时退化为
+            原随机 shuffle。
 
     返回:
         冻结的三池 Pools：diagnosis/validation 仍是逐题 GeneratedQuestion 列表
@@ -173,16 +178,9 @@ def split_by_video_assignment(
     trainval_qs, test_qs = _partition_by_video_assignment(questions, assignment, correctness)
 
     diagnosis, validation = _split_trainval_by_video_group(
-        trainval_qs, correctness, val_ratio, random.Random(seed)
-    )
-
-    if val_wrong_min > 0:
-        val_wrong = sum(1 for q in validation if not correctness[q.question_id])
-        if val_wrong < val_wrong_min:
-            raise InsufficientValSignal(
-                f"validation 池错题数 {val_wrong} < val_wrong_min={val_wrong_min}，"
-                "验证信号不足以支撑可靠比较（如 McNemar 检验功效），"
-                "请放大 val_ratio / 调整 trainval 归属或调低阈值。"
+        trainval_qs, correctness, val_ratio, random.Random(seed),
+        wrong_tier_by_video=wrong_tier_by_video,
+        val_wrong_min=val_wrong_min,
     )
 
     val_correct = sum(1 for q in validation if correctness.get(q.question_id))
@@ -291,6 +289,8 @@ def _split_trainval_by_video_group(
     correctness: dict[str, bool],
     val_ratio: float,
     rng: random.Random,
+    wrong_tier_by_video: dict[str, int] | None = None,
+    val_wrong_min: int = 0,
 ) -> tuple[list[GeneratedQuestion], list[GeneratedQuestion]]:
     """以视频组为原子对 trainval 题集做 correctness 分层，切出 (diagnosis, validation)。
 
@@ -299,6 +299,12 @@ def _split_trainval_by_video_group(
         correctness: question_id -> 基线是否答对；视频组正确性取组内全部题 AND。
         val_ratio: validation 占视频组总数的比例。
         rng: 随机数生成器，保证视频组 shuffle 可复现。
+        wrong_tier_by_video: video_id -> 该视频错题中 T2(defect) 的数量。提供时错题
+            视频组按 T2 含量升序进 val（T2 高的组保留在 diagnosis，把高价值缺陷信号
+            留给诊断），确定性排序取代随机 shuffle；None 时退化为原随机 shuffle。
+        val_wrong_min: validation 池最少错题数（切分时保证功效）。> 0 且初分 val 错题
+            不足时，从 diag 侧的错题组按 T2 升序换入 val 直到满足（每组至多移动一次），
+            耗尽仍不足则抛 InsufficientValSignal（fail loud，P5）。
 
     返回:
         (diagnosis, validation) 逐题列表元组；同一 video 的全部题整组落在同一侧，
@@ -306,7 +312,8 @@ def _split_trainval_by_video_group(
 
     关键实现细节:
         与 _split_one_category 同构：先按视频组 correctness 分正确组/错误组，按比例
-        把 n_val 个组分层落入 validation（全正确或全错误时退化为非分层随机划分），
+        把 n_val 个组分层落入 validation（全正确退化为非分层随机划分；全错误时若有
+        wrong_tier_by_video 仍按 T2 升序分配，否则随机划分），
         再把选中组内所有题展开。视频组按 video_id 排序后再 shuffle，保证确定性。
     """
     groups: dict[str, list[GeneratedQuestion]] = defaultdict(list)
@@ -320,7 +327,11 @@ def _split_trainval_by_video_group(
     correct_vids, wrong_vids = _partition_video_groups_by_correctness(groups, correctness)
     n_correct = len(correct_vids)
 
-    if n_correct == 0 or n_correct == n_total:
+    if n_correct == 0 and wrong_tier_by_video is not None:
+        # 全部错误 + 有 tier 信号：按 T2 升序，低 T2 组优先进 val（保留高 T2 在 diag）
+        wrong_vids.sort(key=lambda v: (wrong_tier_by_video.get(v, 0), v))
+        val_vids = set(wrong_vids[:n_val])
+    elif n_correct == 0 or n_correct == n_total:
         label = "全部正确" if n_correct == n_total else "全部错误"
         logger.warning("trainval 视频组 {} ({} 组)，退化为非分层随机划分", label, n_total)
         shuffled = list(video_ids)
@@ -330,9 +341,33 @@ def _split_trainval_by_video_group(
         val_correct = math.floor(n_correct * n_val / n_total)
         val_wrong = n_val - val_correct
         rng.shuffle(correct_vids)
+        if wrong_tier_by_video is None:
             rng.shuffle(wrong_vids)
+        else:
+            # T2 少的错题组优先进 val（保留 T2 高的组在 diag），确定性排序
+            wrong_vids.sort(key=lambda v: (wrong_tier_by_video.get(v, 0), v))
         val_vids = set(correct_vids[:val_correct] + wrong_vids[:val_wrong])
 
+    if val_wrong_min > 0:
+        val_wrong_now = sum(
+            1 for v in val_vids for q in groups[v] if not correctness[q.question_id]
+        )
+        # diag 侧仍在的错题组，按 T2 升序（低价值优先移交 val）
+        diag_wrong_pool = sorted(
+            (v for v in wrong_vids if v not in val_vids),
+            key=lambda v: ((wrong_tier_by_video or {}).get(v, 0), v),
+        )
+        for v in diag_wrong_pool:
+            if val_wrong_now >= val_wrong_min:
+                break
+            val_vids.add(v)
+            val_wrong_now += sum(1 for q in groups[v] if not correctness[q.question_id])
+        if val_wrong_now < val_wrong_min:
+            raise InsufficientValSignal(
+                f"trainval 错题不足以让 val 达到 val_wrong_min={val_wrong_min}"
+                f"（修复后仅 {val_wrong_now}），请放大 val_ratio 或调整 trainval 归属。"
+            )
+
     diagnosis = [q for q in trainval_qs if q.video_id not in val_vids]
     validation = [q for q in trainval_qs if q.video_id in val_vids]
     return diagnosis, validation

app/harness/video_split_cli.py

@@ -477,8 +477,9 @@ def load_questions_by_id(questions_dir: Path) -> dict[str, GeneratedQuestion]:
 def check_mcnemar_power(pools: Pools, val_wrong_min: int) -> int:
     """校验 validation 池错题数达 McNemar 功效阈，不足即 fail loud。
 
-    build_split 按契约用 split_by_video_assignment(val_wrong_min=0)（不破契约），
-    故功效护栏在 capstone 层单独核验：val 错题数 < 阈 → 验证信号不足以支撑可靠比较。
+    val_wrong_min 已前置到 build_split 内的切分保证功效（不足即从 diag 换入低 T2
+    错题组补足，耗尽 fail-loud）；本函数作切分冻结后的冗余最终确认：val 错题数 < 阈
+    → 验证信号不足以支撑可靠比较。
 
     参数:
         pools: 冻结三池（含 validation 与 correctness）。
@@ -571,6 +572,7 @@ async def run_pipeline(
             select_seed=config.seed,
             val_ratio=config.val_ratio,
             split_seed=config.seed,
+            val_wrong_min=config.val_wrong_min,
         ),
         out_path=out_dir / "pools.json",
         manifest_path=out_dir / "split_manifest.json",

tests/integration/test_build_split_e2e.py

@@ -101,6 +101,7 @@ def test_end_to_end_freezes_valid_pools(tmp_path: Path) -> None:
         select_seed=7,
         val_ratio=0.3,
         split_seed=7,
+        val_wrong_min=0,
     )
 
     result = build_split(

tests/unit/test_pools_video_atomic.py

@@ -135,3 +135,60 @@ def test_baseline_val_accuracy_reflects_validation():
     assert len(pools.validation) == 2
     assert pools.baseline_val_accuracy == pytest.approx(0.5)
     assert pools.diagnosis == []
+
+
+def test_tier_aware_keeps_high_t2_in_diag():
+    """错题视频组按 T2 含量升序进 val：T2 高的组保留在 diagnosis。"""
+    from app.harness.pools import split_by_video_assignment
+    from core.types import GeneratedQuestion
+
+    def _q(qid, vid):
+        return GeneratedQuestion(
+            question_id=qid, video_id=vid, task_type="X", question="q",
+            options=["A", "B"], answer="A", source_nodes=[], difficulty="easy",
+        )
+
+    # 4 个错题视频（每视频 1 题），T2 数分别 2/1/0/0
+    questions = [_q(f"{v}-1", v) for v in ("vA", "vB", "vC", "vD")]
+    assignment = {v: "trainval" for v in ("vA", "vB", "vC", "vD")}
+    correctness = {f"{v}-1": False for v in ("vA", "vB", "vC", "vD")}
+    wrong_tier = {"vA": 2, "vB": 1, "vC": 0, "vD": 0}
+
+    pools = split_by_video_assignment(
+        questions, assignment, correctness, val_ratio=0.5, seed=7,
+        wrong_tier_by_video=wrong_tier,
+    )
+    diag_vids = {q.video_id for q in pools.diagnosis}
+    # T2 最高的 vA 必留 diag；T2=0 的组优先进 val
+    assert "vA" in diag_vids
+    assert "vB" in diag_vids
+
+
+def test_val_wrong_min_repair_pulls_from_diag():
+    """val 错题不足 val_wrong_min 时从 diag 换入低 T2 错题组补足。"""
+    from app.harness.pools import split_by_video_assignment
+    from core.types import GeneratedQuestion
+
+    def _q(qid, vid, correct):
+        return GeneratedQuestion(
+            question_id=qid, video_id=vid, task_type="X", question="q",
+            options=["A", "B"], answer="A", source_nodes=[], difficulty="easy",
+        )
+
+    # 8 错题视频 + 2 正确视频；val_ratio 小使初分 val 错题不足，触发修复
+    vids_wrong = [f"w{i}" for i in range(8)]
+    vids_correct = ["c0", "c1"]
+    questions = [_q(f"{v}-1", v, False) for v in vids_wrong] + [
+        _q(f"{v}-1", v, True) for v in vids_correct
+    ]
+    assignment = {v: "trainval" for v in vids_wrong + vids_correct}
+    correctness = {f"{v}-1": False for v in vids_wrong}
+    correctness.update({f"{v}-1": True for v in vids_correct})
+    wrong_tier = {v: i for i, v in enumerate(vids_wrong)}  # 递增 T2
+
+    pools = split_by_video_assignment(
+        questions, assignment, correctness, val_ratio=0.1, seed=7,
+        wrong_tier_by_video=wrong_tier, val_wrong_min=4,
+    )
+    val_wrong = sum(1 for q in pools.validation if not correctness[q.question_id])
+    assert val_wrong >= 4, f"功效修复后 val 错题 {val_wrong} < 4"