fix: make pools.json freeze atomic + add split manifest

tests/unit/test_atomic_save_pools.py

@@ -0,0 +1,63 @@
+"""pools.json 原子冻结与切分 manifest 的单元测试。
+
+覆盖:
+    - _atomic_write_json 原子写：内容正确、无残留 tmp、可覆盖已有文件。
+    - write_manifest 溯源写：含 baseline_run_id/diag_fingerprint/seed/pools_sha256
+      等键，且 pools_sha256 与给定 pools.json 内容一致。
+"""
+
+from __future__ import annotations
+
+import hashlib
+import json
+
+from app.harness.pools import _atomic_write_json
+from app.harness.split_manifest import write_manifest
+
+
+def test_atomic_write_replaces_and_no_tmp_left(tmp_path):
+    p = tmp_path / "pools.json"
+    _atomic_write_json(p, {"a": 1})
+    assert json.loads(p.read_text())["a"] == 1
+    assert list(tmp_path.glob("*.tmp")) == []  # 无残留 tmp
+
+
+def test_atomic_write_overwrites_existing(tmp_path):
+    p = tmp_path / "pools.json"
+    _atomic_write_json(p, {"a": 1})
+    _atomic_write_json(p, {"a": 2})
+    assert json.loads(p.read_text())["a"] == 2
+    assert list(tmp_path.glob("*.tmp")) == []
+
+
+def test_write_manifest_contains_keys_and_matching_sha256(tmp_path):
+    pools_json_text = json.dumps({"split_mode": "global", "test": []}, ensure_ascii=False)
+    manifest_path = tmp_path / "manifest.json"
+
+    result = write_manifest(
+        manifest_path,
+        baseline_run_id="run-123",
+        diag_fingerprint="fp-abc",
+        seed=42,
+        config={"train_ratio": 0.5},
+        pools_json_text=pools_json_text,
+        coverage_report={"visual": {"train": 3, "val": 1}},
+        generated_at="2026-07-15T00:00:00Z",
+    )
+
+    written = json.loads(manifest_path.read_text())
+    for key in (
+        "baseline_run_id",
+        "diag_fingerprint",
+        "seed",
+        "config",
+        "pools_sha256",
+        "coverage_report",
+        "generated_at",
+    ):
+        assert key in written
+
+    expected_sha = hashlib.sha256(pools_json_text.encode("utf-8")).hexdigest()
+    assert written["pools_sha256"] == expected_sha
+    assert result == written  # 返回值与落盘内容一致
+    assert list(tmp_path.glob("*.tmp")) == []