diff --git a/scripts/build_yolo_dataset.py b/scripts/build_yolo_dataset.py
new file mode 100644
index 0000000..55253d1
--- /dev/null
+++ b/scripts/build_yolo_dataset.py
@@ -0,0 +1,295 @@
+#!/usr/bin/env python
+"""把 Label Studio 的 YOLO 导出装配成可训练的数据集，划分 train/val 放到 data/ 下。
+
+    uv run python scripts/build_yolo_dataset.py \\
+        --export data/film_yolo_shap.zip \\
+        --images runs/boxes_shap_label_studio/images \\
+        --out data/film_yolo
+
+Label Studio 的 YOLO 导出**只有标签**：本地存储的图片它不会打包进去（`get_local_path` 对
+local-files 直接返回磁盘路径，不复制，`YOLO_WITH_IMAGES` 也一样）。所以图片从我们自己准备
+复核材料的那个目录取——文件名是一一对应的。
+
+```
+<export>.zip                       runs/<...>_label_studio/images/
+├── classes.txt                    └── <类别>_<序号>.png
+├── labels/<类别>_<序号>.txt
+└── images/  ← 空的
+```
+
+装配结果：
+
+```
+data/<name>/
+├── images/{train,val}/<类别>_<序号>.png   # 硬链接，不占额外磁盘
+├── labels/{train,val}/<类别>_<序号>.txt
+├── classes.txt                            # 原样沿用导出的顺序
+├── data.yaml
+└── summary.json
+```
+
+**类别顺序以导出的 classes.txt 为准。** Label Studio 的转换器把标签收进 set 再排序编号，
+与 labeling config 里写的顺序无关，也与我们 `generate_boxes.py` 时的顺序无关。标签里的
+class_id 是按导出的顺序写的，所以 data.yaml 必须照抄，不能另排。
+
+**空标签保留为负样本。** 导出后仍为空的图（本例是 normal，预测已在 Label Studio 里批量删掉）
+表示"这张图没有缺陷"，在检测训练里是压低误检的负样本。`--drop-empty` 可以丢掉它们。
+注意：没复核、也没把预测转成标注的任务同样会导成空标签，那种"空"是信息缺失而不是负样本，
+装配前应先在 Label Studio 里用 Create Annotations From Predictions 补上。
+"""
+
+from __future__ import annotations
+
+import argparse
+import json
+import random
+import shutil
+import sys
+import zipfile
+from collections import Counter, defaultdict
+from pathlib import Path
+from typing import NamedTuple
+
+sys.path.insert(0, str(Path(__file__).resolve().parents[1]))
+
+from datasets.yolo import IMAGE_SUFFIXES, write_classes_txt, write_data_yaml  # noqa: E402
+from utils import link_or_copy, setup_logging  # noqa: E402
+
+logger = None
+
+EMPTY = "(无框)"
+
+
+class Sample(NamedTuple):
+    """一张图、它的标签文本，以及分层划分用的类别。"""
+
+    image: Path
+    label_text: str
+    stratum: str
+
+
+class ExportError(RuntimeError):
+    """导出内容不自洽，装配无法继续。"""
+
+
+def read_export(path: Path) -> tuple[list[str], dict[str, str]]:
+    """读 Label Studio 的 YOLO 导出（zip 或已解压目录）。
+
+    Returns:
+        (类别名列表, {文件名主干: 标签文本})
+    """
+    if path.is_dir():
+        classes_file = path / "classes.txt"
+        if not classes_file.exists():
+            raise ExportError(f"{path} 下没有 classes.txt，这不像 Label Studio 的 YOLO 导出")
+        classes = classes_file.read_text(encoding="utf-8").split()
+        labels = {
+            p.stem: p.read_text(encoding="utf-8")
+            for p in sorted((path / "labels").glob("*.txt"))
+        }
+    else:
+        with zipfile.ZipFile(path) as archive:
+            names = archive.namelist()
+            if "classes.txt" not in names:
+                raise ExportError(f"{path} 里没有 classes.txt，这不像 Label Studio 的 YOLO 导出")
+            classes = archive.read("classes.txt").decode("utf-8").split()
+            labels = {
+                Path(name).stem: archive.read(name).decode("utf-8")
+                for name in sorted(names)
+                if name.startswith("labels/") and name.endswith(".txt")
+            }
+    if not classes:
+        raise ExportError("classes.txt 是空的")
+    if not labels:
+        raise ExportError("导出里没有任何标签文件")
+    return classes, labels
+
+
+def parse_boxes(text: str, stem: str, num_classes: int) -> list[int]:
+    """校验一个标签文件，返回其中所有框的类别下标。
+
+    坐标越界或类别越界都直接报错：这类问题在训练时不会崩，只会悄悄拉低指标。
+    """
+    class_ids = []
+    for number, line in enumerate(text.splitlines(), start=1):
+        line = line.strip()
+        if not line:
+            continue
+        parts = line.split()
+        if len(parts) != 5:
+            raise ExportError(f"{stem}.txt 第 {number} 行有 {len(parts)} 个字段，YOLO 需要 5 个：{line!r}")
+        try:
+            class_id = int(parts[0])
+            coordinates = [float(v) for v in parts[1:]]
+        except ValueError as exc:
+            raise ExportError(f"{stem}.txt 第 {number} 行无法解析：{line!r}") from exc
+        if not 0 <= class_id < num_classes:
+            raise ExportError(f"{stem}.txt 第 {number} 行的类别下标 {class_id} 超出 0~{num_classes - 1}")
+        if not all(0.0 <= v <= 1.0 for v in coordinates):
+            raise ExportError(f"{stem}.txt 第 {number} 行的坐标不在 [0,1] 内：{coordinates}")
+        class_ids.append(class_id)
+    return class_ids
+
+
+def collect(
+    classes: list[str], labels: dict[str, str], images_dir: Path
+) -> tuple[list[Sample], list[str]]:
+    """把标签与图片配对，返回 (样本列表, 多余的图片名)。"""
+    samples = []
+    missing = []
+    for stem, text in labels.items():
+        candidates = [
+            images_dir / f"{stem}{suffix}" for suffix in (".png", *IMAGE_SUFFIXES)
+        ]
+        image = next((p for p in candidates if p.exists()), None)
+        if image is None:
+            missing.append(stem)
+            continue
+        class_ids = parse_boxes(text, stem, len(classes))
+        # 分层用"框最多的那个类别"：一张图可能有多个类别的框，人工复核后尤其常见
+        stratum = classes[Counter(class_ids).most_common(1)[0][0]] if class_ids else EMPTY
+        samples.append(Sample(image, text, stratum))
+
+    if missing:
+        raise ExportError(
+            f"有 {len(missing)} 个标签找不到对应的图片，例如 {missing[0]}；"
+            f"--images 是否指向了准备复核材料时的 images/ 目录（当前 {images_dir}）"
+        )
+    known = {s.image.stem for s in samples}
+    extra = sorted(
+        p.stem for p in images_dir.iterdir()
+        if p.suffix.lower() in IMAGE_SUFFIXES and p.stem not in known
+    )
+    return samples, extra
+
+
+def split(samples: list[Sample], val_ratio: float, seed: int) -> dict[str, list[Sample]]:
+    """按类别分层切分。小类只有几十张，随机整体切很容易让它在验证集里挂零。"""
+    grouped: dict[str, list[Sample]] = defaultdict(list)
+    for sample in samples:
+        grouped[sample.stratum].append(sample)
+
+    rng = random.Random(seed)
+    splits: dict[str, list[Sample]] = {"train": [], "val": []}
+    for _stratum, group in sorted(grouped.items()):
+        order = sorted(group, key=lambda s: s.image.name)     # 先定序，结果才可复现
+        rng.shuffle(order)
+        n_val = max(1, round(len(order) * val_ratio)) if len(order) > 1 else 0
+        splits["val"].extend(order[:n_val])
+        splits["train"].extend(order[n_val:])
+    return splits
+
+
+def main() -> int:
+    global logger
+    parser = argparse.ArgumentParser(
+        description=__doc__, formatter_class=argparse.RawDescriptionHelpFormatter
+    )
+    parser.add_argument("--export", required=True, help="Label Studio 的 YOLO 导出（zip 或目录）")
+    parser.add_argument(
+        "--images", required=True, help="图片目录，即准备复核材料时的 <...>_label_studio/images",
+    )
+    parser.add_argument("--out", required=True, help="输出目录，建议放在 data/ 下")
+    parser.add_argument("--val-ratio", type=float, default=0.2)
+    parser.add_argument("--seed", type=int, default=42)
+    parser.add_argument(
+        "--drop-empty", action="store_true",
+        help="丢掉空标签的图。默认保留——它们是压低误检的负样本",
+    )
+    parser.add_argument("--overwrite", action="store_true", help="输出目录已存在时先清空")
+    parser.add_argument("--dry-run", action="store_true", help="只打印计划")
+    args = parser.parse_args()
+
+    out_dir = Path(args.out)
+    logger = setup_logging()
+
+    try:
+        classes, labels = read_export(Path(args.export))
+        samples, extra = collect(classes, labels, Path(args.images))
+    except (ExportError, FileNotFoundError) as exc:
+        logger.error("%s", exc)
+        return 1
+
+    logger.info("导出: %s（%d 个标签，%d 类）", args.export, len(labels), len(classes))
+    if extra:
+        logger.warning(
+            "%s 里有 %d 张图片没有对应的标签，不会进入数据集（例如 %s）",
+            args.images, len(extra), extra[0],
+        )
+
+    empty = [s for s in samples if s.stratum == EMPTY]
+    if args.drop_empty:
+        samples = [s for s in samples if s.stratum != EMPTY]
+    logger.info(
+        "空标签 %d 张（%.1f%%）：%s",
+        len(empty), 100 * len(empty) / max(len(labels), 1),
+        "已丢弃" if args.drop_empty else "保留为负样本",
+    )
+
+    splits = split(samples, args.val_ratio, args.seed)
+    counts = {name: Counter(s.stratum for s in items) for name, items in splits.items()}
+    boxes = Counter()
+    for sample in samples:
+        for line in sample.label_text.splitlines():
+            if line.strip():
+                boxes[classes[int(line.split()[0])]] += 1
+
+    logger.info("划分: train %d / val %d", len(splits["train"]), len(splits["val"]))
+    logger.info("%-12s %8s %8s %8s", "类别", "train", "val", "框数")
+    for name in [*classes, EMPTY]:
+        if counts["train"][name] or counts["val"][name]:
+            logger.info(
+                "%-12s %8d %8d %8d",
+                name, counts["train"][name], counts["val"][name], boxes[name],
+            )
+
+    if args.dry_run:
+        logger.info("--dry-run：未写入任何文件")
+        return 0
+
+    if out_dir.exists() and any(out_dir.iterdir()):
+        if not args.overwrite:
+            logger.error("%s 已存在且非空；确认要覆盖请加 --overwrite", out_dir)
+            return 1
+        shutil.rmtree(out_dir)
+
+    modes: Counter[str] = Counter()
+    for name, items in splits.items():
+        for sample in items:
+            modes[link_or_copy(sample.image, out_dir / "images" / name / sample.image.name)] += 1
+            label_path = out_dir / "labels" / name / f"{sample.image.stem}.txt"
+            label_path.parent.mkdir(parents=True, exist_ok=True)
+            label_path.write_text(sample.label_text, encoding="utf-8")
+
+    write_data_yaml(out_dir / "data.yaml", classes, root=out_dir.resolve(),
+                    train="images/train", val="images/val")
+    write_classes_txt(out_dir / "classes.txt", classes)
+    (out_dir / "summary.json").write_text(
+        json.dumps(
+            {
+                "export": str(Path(args.export).resolve()),
+                "images": str(Path(args.images).resolve()),
+                "num_images": len(samples),
+                "num_boxes": sum(boxes.values()),
+                "empty_labels": len(empty),
+                "dropped_empty": args.drop_empty,
+                "images_without_label": len(extra),
+                "val_ratio": args.val_ratio,
+                "seed": args.seed,
+                "split_sizes": {k: len(v) for k, v in splits.items()},
+                "per_class_images": {k: dict(v) for k, v in counts.items()},
+                "per_class_boxes": dict(boxes),
+                "link_modes": dict(modes),
+            },
+            ensure_ascii=False,
+            indent=2,
+        ),
+        encoding="utf-8",
+    )
+    logger.info("图片落盘方式: %s", dict(modes))
+    logger.info("完成 -> %s（%d 个框）", out_dir, sum(boxes.values()))
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())
diff --git a/scripts/prepare_label_studio.py b/scripts/prepare_label_studio.py
index f149897..fb8e156 100644
--- a/scripts/prepare_label_studio.py
+++ b/scripts/prepare_label_studio.py
@@ -55,7 +55,6 @@ from __future__ import annotations
 import argparse
 import contextlib
 import csv
-import errno
 import io
 import json
 import logging
@@ -73,7 +72,7 @@ sys.path.insert(0, str(Path(__file__).resolve().parents[1]))
 import yaml  # noqa: E402
 
 from datasets.yolo import IMAGE_SUFFIXES, write_classes_txt  # noqa: E402
-from utils import setup_logging  # noqa: E402
+from utils import link_or_copy, setup_logging  # noqa: E402
 
 logger = None
 
@@ -116,21 +115,6 @@ def materialize_png(source: Path, destination: Path) -> str:
     return "convert"
 
 
-def link_or_copy(source: Path, destination: Path) -> str:
-    """硬链接；跨文件系统时退回复制。"""
-    if destination.exists() or destination.is_symlink():
-        destination.unlink()
-    destination.parent.mkdir(parents=True, exist_ok=True)
-    try:
-        os.link(source, destination)
-        return "hard"
-    except OSError as exc:
-        if exc.errno != errno.EXDEV:
-            raise
-        shutil.copy2(source, destination)
-        return "copy"
-
-
 class Sample(NamedTuple):
     """一张图及其标签。
 
diff --git a/tests/test_build_yolo_dataset.py b/tests/test_build_yolo_dataset.py
new file mode 100644
index 0000000..f3a9eda
--- /dev/null
+++ b/tests/test_build_yolo_dataset.py
@@ -0,0 +1,229 @@
+"""把 Label Studio 的 YOLO 导出装配成带 train/val 划分的数据集。"""
+
+import json
+import sys
+import zipfile
+from pathlib import Path
+
+import pytest
+
+pytest.importorskip("PIL")
+
+import numpy as np  # noqa: E402
+import yaml  # noqa: E402
+from PIL import Image  # noqa: E402
+
+sys.path.insert(0, "scripts")
+import build_yolo_dataset as byd  # noqa: E402
+
+#: 与 Label Studio 导出一致：类别按字母序，标签里的 class_id 就是这个顺序的下标
+CLASSES = ["blackdot", "grease", "normal", "wrinkle"]
+
+#: {文件名主干: 标签内容}。normal 是空标签（负样本），wrinkle_0001 有两个不同类别的框
+LABELS = {
+    "blackdot_0001": "0 0.5 0.5 0.1 0.1\n",
+    "blackdot_0002": "0 0.2 0.3 0.1 0.1\n",
+    "blackdot_0003": "0 0.6 0.6 0.2 0.2\n",
+    "grease_0001": "1 0.4 0.4 0.3 0.3\n",
+    "grease_0002": "1 0.5 0.5 0.2 0.2\n",
+    "wrinkle_0001": "3 0.5 0.5 0.4 0.4\n0 0.1 0.1 0.05 0.05\n3 0.8 0.8 0.1 0.1\n",
+    "wrinkle_0002": "3 0.3 0.3 0.3 0.3\n",
+    "normal_0001": "",
+    "normal_0002": "",
+    "normal_0003": "",
+}
+
+
+@pytest.fixture
+def export(tmp_path):
+    """一个 zip 形式的导出 + 与之配套的图片目录。"""
+    images = tmp_path / "label_studio" / "images"
+    images.mkdir(parents=True)
+    rng = np.random.default_rng(0)
+    for stem in LABELS:
+        Image.fromarray(rng.integers(0, 255, (32, 40, 3), dtype=np.uint8)).save(
+            images / f"{stem}.png"
+        )
+
+    archive = tmp_path / "export.zip"
+    with zipfile.ZipFile(archive, "w") as zipped:
+        zipped.writestr("classes.txt", "".join(f"{c}\n" for c in CLASSES))
+        zipped.writestr("notes.json", "{}")
+        for stem, text in LABELS.items():
+            zipped.writestr(f"labels/{stem}.txt", text)
+    return archive, images
+
+
+def run(export, out, *extra):
+    archive, images = export
+    argv = ["build_yolo_dataset.py", "--export", str(archive), "--images", str(images),
+            "--out", str(out), *extra]
+    original, sys.argv = sys.argv, argv
+    try:
+        return byd.main()
+    finally:
+        sys.argv = original
+
+
+def outputs(out, kind):
+    return {p.stem: p for split in ("train", "val") for p in (out / kind / split).iterdir()}
+
+
+def test_builds_a_split_dataset(export, tmp_path):
+    out = tmp_path / "data" / "film"
+    assert run(export, out) == 0
+
+    images, labels = outputs(out, "images"), outputs(out, "labels")
+    assert set(images) == set(LABELS) == set(labels)
+    for stem, path in labels.items():
+        assert path.read_text(encoding="utf-8") == LABELS[stem]
+        # 图与标签必须落在同一个 split，否则验证集会混进训练图
+        assert path.parent.name == images[stem].parent.name
+
+
+def test_class_order_comes_from_the_export(export, tmp_path):
+    """类别顺序必须照抄导出的 classes.txt：标签里的 class_id 是按它写的。"""
+    out = tmp_path / "data" / "film"
+    assert run(export, out) == 0
+
+    meta = yaml.safe_load((out / "data.yaml").read_text(encoding="utf-8"))
+    assert [meta["names"][i] for i in range(meta["nc"])] == CLASSES
+    assert (out / "classes.txt").read_text(encoding="utf-8").split() == CLASSES
+    assert Path(meta["path"]).is_absolute()
+    assert meta["train"] == "images/train" and meta["val"] == "images/val"
+
+
+def test_images_are_hard_linked(export, tmp_path):
+    _, images_dir = export
+    out = tmp_path / "data" / "film"
+    assert run(export, out) == 0
+
+    linked = outputs(out, "images")["grease_0001"]
+    assert linked.stat().st_ino == (images_dir / "grease_0001.png").stat().st_ino
+    assert json.loads((out / "summary.json").read_text(encoding="utf-8"))["link_modes"] == {
+        "hard": len(LABELS)
+    }
+
+
+def test_small_classes_appear_in_both_splits(export, tmp_path):
+    """分层切分：三张图的类别也要在验证集里留下一张。"""
+    out = tmp_path / "data" / "film"
+    assert run(export, out) == 0
+    per_class = json.loads((out / "summary.json").read_text(encoding="utf-8"))["per_class_images"]
+    for name in ("blackdot", "(无框)"):
+        assert per_class["train"][name] >= 1 and per_class["val"][name] == 1
+
+
+def test_multi_class_image_is_stratified_by_its_dominant_class(export, tmp_path):
+    """一张图可能有多个类别的框（人工复核后常见），按框最多的类别分层。"""
+    out = tmp_path / "data" / "film"
+    assert run(export, out) == 0
+    summary = json.loads((out / "summary.json").read_text(encoding="utf-8"))
+    # wrinkle_0001 有 2 个 wrinkle 框 + 1 个 blackdot 框 -> 计入 wrinkle
+    assert summary["per_class_images"]["train"].get("wrinkle", 0) + summary[
+        "per_class_images"
+    ]["val"].get("wrinkle", 0) == 2
+    # 框数按每个框各自的类别统计
+    assert summary["per_class_boxes"] == {"blackdot": 4, "grease": 2, "wrinkle": 3}
+    assert summary["num_boxes"] == 9
+
+
+def test_empty_labels_kept_as_negatives_by_default(export, tmp_path):
+    out = tmp_path / "data" / "film"
+    assert run(export, out) == 0
+    summary = json.loads((out / "summary.json").read_text(encoding="utf-8"))
+    assert summary["empty_labels"] == 3
+    assert summary["num_images"] == 10
+    assert outputs(out, "labels")["normal_0001"].read_text(encoding="utf-8") == ""
+
+    dropped = tmp_path / "data" / "dropped"
+    assert run(export, dropped, "--drop-empty") == 0
+    assert json.loads((dropped / "summary.json").read_text(encoding="utf-8"))["num_images"] == 7
+    assert "normal_0001" not in outputs(dropped, "images")
+
+
+def test_reads_an_extracted_directory_too(export, tmp_path):
+    """zip 与解压后的目录应当等价。"""
+    archive, images = export
+    extracted = tmp_path / "extracted"
+    with zipfile.ZipFile(archive) as zipped:
+        zipped.extractall(extracted)
+
+    from_zip, from_dir = tmp_path / "a", tmp_path / "b"
+    assert run(export, from_zip) == 0
+    assert run((extracted, images), from_dir) == 0
+    assert sorted(outputs(from_zip, "images")) == sorted(outputs(from_dir, "images"))
+
+
+def test_missing_image_is_an_error(export, tmp_path, capsys):
+    """标签找不到图就报错，而不是悄悄少装配一张。"""
+    _, images = export
+    (images / "grease_0001.png").unlink()
+    assert run(export, tmp_path / "out") != 0
+    assert "找不到对应的图片" in capsys.readouterr().out
+
+
+def test_extra_images_are_reported(export, tmp_path, capsys):
+    """图片多于标签时告警——多半是 --images 指错了目录或导出不完整。"""
+    _, images = export
+    Image.fromarray(np.zeros((8, 8, 3), dtype=np.uint8)).save(images / "stray_0001.png")
+    assert run(export, tmp_path / "out") == 0
+    assert "没有对应的标签" in capsys.readouterr().out
+
+
+@pytest.mark.parametrize(
+    "text,expected",
+    [
+        ("0 0.5 0.5 0.1\n", "需要 5 个"),          # 字段数不对
+        ("9 0.5 0.5 0.1 0.1\n", "超出"),           # 类别下标越界
+        ("0 0.5 1.5 0.1 0.1\n", "不在 [0,1]"),     # 坐标越界
+        ("x 0.5 0.5 0.1 0.1\n", "无法解析"),
+    ],
+)
+def test_malformed_labels_are_rejected(export, tmp_path, capsys, text, expected):
+    """坏标签在训练时不会崩，只会悄悄拉低指标，所以这里必须拦住。"""
+    archive, images = export
+    broken = tmp_path / "broken.zip"
+    with zipfile.ZipFile(archive) as source, zipfile.ZipFile(broken, "w") as target:
+        for item in source.namelist():
+            data = source.read(item)
+            if item == "labels/grease_0001.txt":
+                data = text.encode("utf-8")
+            target.writestr(item, data)
+
+    assert run((broken, images), tmp_path / "out") != 0
+    assert expected in capsys.readouterr().out
+
+
+def test_not_a_label_studio_export(tmp_path, capsys):
+    empty = tmp_path / "empty"
+    (empty / "labels").mkdir(parents=True)
+    assert run((empty, tmp_path), tmp_path / "out") != 0
+    assert "classes.txt" in capsys.readouterr().out
+
+
+def test_split_is_reproducible_and_ratio_respected(export, tmp_path):
+    first, second = tmp_path / "a", tmp_path / "b"
+    assert run(export, first, "--seed", "7") == 0
+    assert run(export, second, "--seed", "7") == 0
+    assert sorted(outputs(first, "images")) == sorted(outputs(second, "images"))
+    for split in ("train", "val"):
+        assert sorted(p.name for p in (first / "images" / split).iterdir()) == sorted(
+            p.name for p in (second / "images" / split).iterdir()
+        )
+
+    # 比例是按每个分层分别取整的：blackdot 3 张 -> 2 张进验证集，所以合计不是对半
+    other = tmp_path / "c"
+    assert run(export, other, "--val-ratio", "0.5") == 0
+    sizes = json.loads((other / "summary.json").read_text(encoding="utf-8"))["split_sizes"]
+    assert sizes["val"] == 6 and sizes["train"] == 4
+
+
+def test_refuses_to_clobber_and_dry_run_writes_nothing(export, tmp_path):
+    out = tmp_path / "data" / "film"
+    assert run(export, out, "--dry-run") == 0
+    assert not out.exists()
+
+    assert run(export, out) == 0
+    assert run(export, out) != 0                  # 已存在且非空
+    assert run(export, out, "--overwrite") == 0
diff --git a/utils/__init__.py b/utils/__init__.py
index d7cad96..8c11c35 100644
--- a/utils/__init__.py
+++ b/utils/__init__.py
@@ -1,4 +1,4 @@
-"""通用工具：配置、注册表、日志、随机种子、设备检查。"""
+"""通用工具：配置、注册表、日志、随机种子、设备检查、文件落盘。"""
 
 from utils.config import Config, load_config
 from utils.device import (
@@ -10,6 +10,7 @@ from utils.device import (
     resolve_amp,
     resolve_device,
 )
+from utils.fs import link_or_copy
 from utils.logging import get_logger, setup_logging
 from utils.registry import Registry
 from utils.seed import seed_everything
@@ -28,4 +29,5 @@ __all__ = [
     "setup_logging",
     "Registry",
     "seed_everything",
+    "link_or_copy",
 ]
diff --git a/utils/fs.py b/utils/fs.py
new file mode 100644
index 0000000..002aee9
--- /dev/null
+++ b/utils/fs.py
@@ -0,0 +1,28 @@
+"""文件落盘的小工具。"""
+
+from __future__ import annotations
+
+import errno
+import os
+import shutil
+from pathlib import Path
+
+
+def link_or_copy(source: str | Path, destination: str | Path) -> str:
+    """给文件建硬链接；跨文件系统时退回复制。返回 "hard" 或 "copy"。
+
+    硬链接不占额外磁盘，却表现得和真实文件一样——产出目录可以整个拷走。
+    数据集动辄上万张图，链接与复制的差别是几百 MB 起步。
+    """
+    destination = Path(destination)
+    if destination.exists() or destination.is_symlink():
+        destination.unlink()
+    destination.parent.mkdir(parents=True, exist_ok=True)
+    try:
+        os.link(source, destination)
+        return "hard"
+    except OSError as exc:
+        if exc.errno != errno.EXDEV:
+            raise
+        shutil.copy2(source, destination)
+        return "copy"