diff --git a/core/evolution/validate.py b/core/evolution/validate.py
new file mode 100644
index 0000000..5c140fd
--- /dev/null
+++ b/core/evolution/validate.py
@@ -0,0 +1,85 @@
+"""core/evolution/validate.py — 块验证纯决策函数。
+
+算法 #7（块顺序验证）的局部实现：pair_block 逐题比对基线与候选、
+classify_quadrants 四象限分类、compute_accuracy 纯算术准确率。
+
+三个函数均为纯函数，无副作用、无外部依赖。
+"""
+
+from core.evolution.types import PairResult, QuadrantClassification
+
+
+def pair_block(
+    baseline: dict[str, bool],
+    candidate: dict[str, bool],
+    question_ids: list[str],
+) -> PairResult:
+    """逐题比对基线与候选对错，统计翻转。
+
+    参数:
+        baseline: 基线臂每题正确性映射。
+        candidate: 候选臂每题正确性映射。
+        question_ids: 参与比对的题目 ID 列表。
+
+    返回:
+        PairResult，包含 w（基线错→候选对翻转数）、l（基线对→候选错翻转数）
+        和 observed（每题的 (基线, 候选) 对错记录）。
+    """
+    w = l = 0  # noqa: E741 — 数学记号 W/L（win/loss），与 gate.py 一致
+    observed: dict[str, tuple[bool, bool]] = {}
+    for qid in question_ids:
+        b, c = baseline[qid], candidate[qid]
+        observed[qid] = (b, c)
+        if not b and c:
+            w += 1
+        elif b and not c:
+            l += 1  # noqa: E741
+    return PairResult(w=w, l=l, observed=observed)
+
+
+def classify_quadrants(
+    observed: dict[str, tuple[bool, bool]],
+) -> QuadrantClassification:
+    """按 (baseline, candidate) 四组分类，各组内 sorted。
+
+    参数:
+        observed: 每题的 (基线是否正确, 候选是否正确) 记录。
+
+    返回:
+        QuadrantClassification，四个象限各含排序后的题目 ID 列表。
+    """
+    improvements: list[str] = []
+    regressions: list[str] = []
+    persistent_fails: list[str] = []
+    stable_successes: list[str] = []
+    for qid, (prev, curr) in observed.items():
+        if not prev and curr:
+            improvements.append(qid)
+        elif prev and not curr:
+            regressions.append(qid)
+        elif not prev and not curr:
+            persistent_fails.append(qid)
+        else:
+            stable_successes.append(qid)
+    return QuadrantClassification(
+        improvements=sorted(improvements),
+        regressions=sorted(regressions),
+        persistent_fails=sorted(persistent_fails),
+        stable_successes=sorted(stable_successes),
+    )
+
+
+def compute_accuracy(
+    correctness: dict[str, bool],
+    question_ids: list[str],
+) -> float:
+    """纯算术：sum(correct) / len(ids)。
+
+    参数:
+        correctness: 每题正确性映射。
+        question_ids: 参与计算的题目 ID 列表。
+
+    返回:
+        准确率浮点数。question_ids 为空时抛出 ZeroDivisionError。
+    """
+    return sum(correctness[qid] for qid in question_ids) / len(question_ids)
diff --git a/tests/unit/test_validate.py b/tests/unit/test_validate.py
new file mode 100644
index 0000000..a90a8dc
--- /dev/null
+++ b/tests/unit/test_validate.py
@@ -0,0 +1,105 @@
+"""tests/unit/test_validate.py — 块验证纯决策函数的单元测试。"""
+
+import pytest
+
+from core.evolution.validate import classify_quadrants, compute_accuracy, pair_block
+
+
+class TestPairBlock:
+    """pair_block 逐题比对基线与候选的翻转统计测试。"""
+
+    def test_basic_flips(self) -> None:
+        """基本翻转：一题从错到对(w)、一题从对到错(l)、一题不变。"""
+        baseline = {"q1": False, "q2": True, "q3": True}
+        candidate = {"q1": True, "q2": False, "q3": True}
+        result = pair_block(baseline, candidate, ["q1", "q2", "q3"])
+        assert result.w == 1
+        assert result.l == 1
+        assert result.observed == {
+            "q1": (False, True),
+            "q2": (True, False),
+            "q3": (True, True),
+        }
+
+    def test_empty(self) -> None:
+        """空输入应返回零翻转。"""
+        result = pair_block({}, {}, [])
+        assert result.w == 0 and result.l == 0
+
+    def test_all_wins(self) -> None:
+        """全部从错到对的极端情况。"""
+        baseline = {"q1": False, "q2": False}
+        candidate = {"q1": True, "q2": True}
+        result = pair_block(baseline, candidate, ["q1", "q2"])
+        assert result.w == 2
+        assert result.l == 0
+
+    def test_all_losses(self) -> None:
+        """全部从对到错的极端情况。"""
+        baseline = {"q1": True, "q2": True}
+        candidate = {"q1": False, "q2": False}
+        result = pair_block(baseline, candidate, ["q1", "q2"])
+        assert result.w == 0
+        assert result.l == 2
+
+    def test_subset_of_questions(self) -> None:
+        """只对 question_ids 中指定的子集进行比对。"""
+        baseline = {"q1": False, "q2": True, "q3": True}
+        candidate = {"q1": True, "q2": False, "q3": True}
+        result = pair_block(baseline, candidate, ["q1"])
+        assert result.w == 1
+        assert result.l == 0
+        assert "q2" not in result.observed
+
+
+class TestClassifyQuadrants:
+    """classify_quadrants 四象限分类测试。"""
+
+    def test_all_four(self) -> None:
+        """四个象限各有一题。"""
+        observed = {
+            "q1": (False, True),
+            "q2": (True, False),
+            "q3": (False, False),
+            "q4": (True, True),
+        }
+        qc = classify_quadrants(observed)
+        assert qc.improvements == ["q1"]
+        assert qc.regressions == ["q2"]
+        assert qc.persistent_fails == ["q3"]
+        assert qc.stable_successes == ["q4"]
+
+    def test_sorted_within_quadrant(self) -> None:
+        """同象限内题目 ID 应按字典序排列。"""
+        observed = {"z": (False, True), "a": (False, True)}
+        qc = classify_quadrants(observed)
+        assert qc.improvements == ["a", "z"]
+
+    def test_empty_observed(self) -> None:
+        """空输入应返回全空象限。"""
+        qc = classify_quadrants({})
+        assert qc.improvements == []
+        assert qc.regressions == []
+        assert qc.persistent_fails == []
+        assert qc.stable_successes == []
+
+
+class TestComputeAccuracy:
+    """compute_accuracy 准确率计算测试。"""
+
+    def test_basic(self) -> None:
+        """一对一错，准确率 0.5。"""
+        assert compute_accuracy({"q1": True, "q2": False}, ["q1", "q2"]) == 0.5
+
+    def test_all_correct(self) -> None:
+        """全部正确，准确率 1.0。"""
+        assert compute_accuracy({"q1": True, "q2": True}, ["q1", "q2"]) == 1.0
+
+    def test_all_wrong(self) -> None:
+        """全部错误，准确率 0.0。"""
+        assert compute_accuracy({"q1": False, "q2": False}, ["q1", "q2"]) == 0.0
+
+    def test_empty_raises(self) -> None:
+        """空题目列表应抛出 ZeroDivisionError。"""
+        with pytest.raises(ZeroDivisionError):
+            compute_accuracy({}, [])