diff --git a/music_api/api.py b/music_api/api.py
index 2c3944d..8e740cc 100644
--- a/music_api/api.py
+++ b/music_api/api.py
@@ -29,10 +29,9 @@ from .errors import (
 )
 
 
-def _map_song_item(item: dict[str, Any]) -> dict[str, Any]:
-    """歌曲条目映射。"""
+def _song_base_fields(item: dict[str, Any]) -> dict[str, Any]:
+    """歌曲条目公共字段（搜索四路与歌单详情共用同一容错口径）。"""
     return {
-        'type': 'song',
         'id': item['id'],
         'name': item.get('name') or '未知歌曲',
         'artists': '/'.join(filter(None, (a.get('name') for a in item.get('ar') or []))) or '未知歌手',
@@ -41,6 +40,57 @@ def _map_song_item(item: dict[str, Any]) -> dict[str, Any]:
     }
 
 
+def _map_song_item(item: dict[str, Any]) -> dict[str, Any]:
+    """歌曲条目映射。"""
+    return {
+        'type': 'song',
+        **_song_base_fields(item)
+    }
+
+
+def _playlist_track_ids(playlist: dict[str, Any]) -> list[str]:
+    """trackIds → 字符串 ID 列表（缺 id 的条目跳过）。"""
+    return [str(t['id']) for t in (playlist.get('trackIds') or []) if t.get('id')]
+
+
+async def _collect_playlist_tracks(track_ids: list[str], headers: dict[str, str],
+                                   cookies: dict[str, str]) -> tuple[list[dict[str, Any]], int]:
+    """分批拉取歌单全部曲目明细，返回 (tracks, failed_batches)。
+
+    明细批次的业务 code 也要校验，失败批次记入 failed_batches，不再静默缺歌。
+    脏 ID 跳过整批（'①'.isdigit() 为真但 int() 抛 ValueError——原实现此处
+    未捕获会整歌单 500，现为跳批）；明细缺 id 的歌跳过不拖整批。
+    """
+    tracks: list[dict[str, Any]] = []
+    failed_batches = 0
+    for i in range(0, len(track_ids), 100):
+        batch_ids = track_ids[i:i + 100]
+        try:
+            song_data = {'c': json.dumps([{'id': int(sid), 'v': 0} for sid in batch_ids
+                                          if str(sid).isdigit()])}
+        except (TypeError, ValueError):
+            continue
+
+        song_resp = await requests.post(APIConstants.SONG_DETAIL_V3, data=song_data,
+                                        headers=headers, cookies=cookies, timeout=30)
+        song_resp.raise_for_status()
+
+        song_result = song_resp.json()
+        if not isinstance(song_result, dict):
+            # 上游 null/数组体按失败批次计，不让 AttributeError 失真
+            failed_batches += 1
+            continue
+        if song_result.get('code') != 200:
+            # 本批次业务失败：计为失败批次，交付方可见残缺状态
+            failed_batches += 1
+            continue
+        for song in (song_result.get('songs') or []):
+            if not song.get('id'):
+                continue
+            tracks.append(_song_base_fields(song))
+    return tracks, failed_batches
+
+
 def _map_album_item(item: dict[str, Any]) -> dict[str, Any]:
     """专辑条目映射（artists 为空**不**兜底成"未知歌手"——与歌曲路不同口径）。"""
     return {
@@ -286,7 +336,7 @@ class NeteaseAPI:
             cookies: 用户cookies
 
         Returns:
-            歌单详情信息
+            歌单详情信息（曲目数与 trackIds 不一致时附 incomplete/missing/failed_batches）
 
         Raises:
             APIException: API调用失败时抛出
@@ -324,47 +374,13 @@ class NeteaseAPI:
                 'tracks': []
             }
 
-            # 获取所有trackIds并分批获取详细信息（明细批次的业务 code 也要校验，
-            # 失败批次记入 failed_batches，不再静默缺歌）
-            track_ids = [str(t['id']) for t in (playlist.get('trackIds') or []) if t.get('id')]
-            failed_batches = 0
-            for i in range(0, len(track_ids), 100):
-                batch_ids = track_ids[i:i+100]
-                # trackIds 混入非数字脏 ID 时跳过该条（原实现 int 抛 ValueError
-                # 不在捕获列表，整歌单 500）；明细缺 id 的歌跳过不拖整批
-                try:
-                    song_data = {'c': json.dumps([{'id': int(sid), 'v': 0} for sid in batch_ids
-                                                  if str(sid).isdigit()])}
-                except (TypeError, ValueError):
-                    continue
-
-                song_resp = await requests.post(APIConstants.SONG_DETAIL_V3, data=song_data,
-                                        headers=headers, cookies=cookies, timeout=30)
-                song_resp.raise_for_status()
-
-                song_result = song_resp.json()
-                if not isinstance(song_result, dict):
-                    # 上游 null/数组体按失败批次计，不让 AttributeError 失真
-                    failed_batches += 1
-                    continue
-                if song_result.get('code') != 200:
-                    # 本批次业务失败：计为失败批次，交付方可见残缺状态
-                    failed_batches += 1
-                    continue
-                for song in (song_result.get('songs') or []):
-                    if not song.get('id'):
-                        continue
-                    info['tracks'].append({
-                        'id': song['id'],
-                        'name': song.get('name') or '未知歌曲',
-                        'artists': '/'.join(filter(None, (a.get('name') for a in song.get('ar') or []))) or '未知歌手',
-                        'album': (song.get('al') or {}).get('name') or '未知专辑',
-                        'picUrl': (song.get('al') or {}).get('picUrl') or ''
-                    })
+            track_ids = _playlist_track_ids(playlist)
+            tracks, failed_batches = await _collect_playlist_tracks(track_ids, headers, cookies)
+            info['tracks'] = tracks
             # trackIds 数与实际拿到的不一致时显式标记"不完整"，不冒充完整结果
-            if len(info['tracks']) != len(track_ids):
+            if len(tracks) != len(track_ids):
                 info['incomplete'] = True
-                info['missing'] = len(track_ids) - len(info['tracks'])
+                info['missing'] = len(track_ids) - len(tracks)
                 info['failed_batches'] = failed_batches
 
             return info
diff --git a/tests/test_playlist_detail.py b/tests/test_playlist_detail.py
new file mode 100644
index 0000000..65db6d6
--- /dev/null
+++ b/tests/test_playlist_detail.py
@@ -0,0 +1,211 @@
+# -*- coding: utf-8 -*-
+"""get_playlist_detail 的行为契约测试（沙箱，不触真实上游）。
+
+为什么：歌单详情是「歌单解析」功能的唯一上游通道（94 行 / 批次拉取 /
+嵌套 3），此前零测试覆盖。它的容错口径都是对外可观察行为：
+- 上游 code:200 + playlist:null →「歌单不存在或无权访问」（路由统一转 404）
+- 明细批次业务失败计 failed_batches，不静默缺歌
+- trackIds 混入脏 ID（如带圈数字——isdigit() 为真但 int() 抛错）跳过整批
+- trackIds 数与实得数不一致时显式标 incomplete/missing
+
+按惯例：先在未改动的原始实现上跑绿，重构时这批测试即等价性验证器。
+替身边界：monkeypatch ``music_api.api.requests.post``，按 URL 分流——
+PLAYLIST_DETAIL_API 与 SONG_DETAIL_V3 分别给响应替身。
+"""
+import json
+from typing import Any
+
+import pytest
+
+from music_api import APIException
+from music_api import api as api_mod
+from music_api.api import NeteaseAPI
+from music_api.constants import APIConstants
+
+_API = NeteaseAPI()
+
+
+class _FakeResp:
+    """``requests.post`` 响应替身：json 载荷或注入异常。"""
+
+    def __init__(self, payload: Any = None, *,
+                 status_error: Exception | None = None,
+                 json_error: Exception | None = None):
+        self.payload = payload
+        self.status_error = status_error
+        self.json_error = json_error
+
+    def raise_for_status(self) -> None:
+        if self.status_error is not None:
+            raise self.status_error
+
+    def json(self) -> Any:
+        if self.json_error is not None:
+            raise self.json_error
+        return self.payload
+
+
+@pytest.fixture()
+def api_capture(monkeypatch):
+    """按 URL 分流的 requests.post 替身：歌单详情响应固定，批次响应按序消费。"""
+    calls: list[dict[str, Any]] = []
+    state: dict[str, Any] = {
+        'playlist_resp': _FakeResp({'code': 200, 'playlist': {}}),
+        'batch_resps': [_FakeResp({'code': 200, 'songs': []})],
+    }
+
+    async def _fake_post(url: str, **kw: Any):
+        calls.append({'url': url, 'data': kw.get('data')})
+        if url == APIConstants.PLAYLIST_DETAIL_API:
+            return state['playlist_resp']
+        assert url == APIConstants.SONG_DETAIL_V3, f'unexpected url: {url}'
+        if not state['batch_resps']:
+            raise AssertionError('批次响应耗尽')
+        return state['batch_resps'].pop(0)
+
+    monkeypatch.setattr(api_mod.requests, 'post', _fake_post)
+    state['calls'] = calls
+    return state
+
+
+def _playlist_payload(playlist: dict[str, Any]) -> _FakeResp:
+    return _FakeResp({'code': 200, 'playlist': playlist})
+
+
+def _batch_c_payloads(calls: list[dict[str, Any]]) -> list[list[int]]:
+    """从捕获的调用里提取每批的 c 载荷（id 列表）。"""
+    out = []
+    for c in calls:
+        if c['url'] == APIConstants.SONG_DETAIL_V3:
+            ids = [e['id'] for e in json.loads(c['data']['c'])]
+            out.append(ids)
+    return out
+
+
+async def _detail(api_capture, playlist: dict[str, Any]) -> dict[str, Any]:
+    api_capture['playlist_resp'] = _playlist_payload(playlist)
+    return await _API.get_playlist_detail(123, {})
+
+
+# ============ 歌单头 ============
+
+async def test_playlist_null_is_apiexception(api_capture):
+    """上游对不存在/私密歌单返回 code:200 + playlist:null → 显式 APIException。"""
+    api_capture['playlist_resp'] = _playlist_payload({})
+    with pytest.raises(APIException, match='歌单不存在或无权访问'):
+        await _API.get_playlist_detail(123, {})
+
+
+async def test_business_code_error(api_capture):
+    api_capture['playlist_resp'] = _FakeResp({'code': 512, 'message': '需要登录'})
+    with pytest.raises(APIException, match='获取歌单详情失败: 需要登录'):
+        await _API.get_playlist_detail(123, {})
+
+
+async def test_non_dict_response(api_capture):
+    api_capture['playlist_resp'] = _FakeResp(None)
+    with pytest.raises(APIException, match='响应格式异常'):
+        await _API.get_playlist_detail(123, {})
+
+
+# ============ 成功主路径 ============
+
+async def test_success_maps_tracks(api_capture):
+    api_capture['playlist_resp'] = _playlist_payload({
+        'id': 123, 'name': '歌单A', 'coverImgUrl': 'https://cover/1',
+        'creator': {'nickname': '作者'}, 'trackCount': 2,
+        'trackIds': [{'id': 1}, {'id': 2}, {'id': None}],
+    })
+    api_capture['batch_resps'] = [_FakeResp({'code': 200, 'songs': [
+        {'id': 1, 'name': '歌A', 'ar': [{'name': '歌手X'}],
+         'al': {'name': '专辑Z', 'picUrl': 'https://pic/1.jpg'}},
+        {'id': None, 'name': '残缺'},
+        {'id': 2, 'name': '歌B', 'ar': [], 'al': {}},
+    ]})]
+
+    out = await _API.get_playlist_detail(123, {})
+    assert out['name'] == '歌单A'
+    assert out['creator'] == '作者'
+    assert out['tracks'] == [
+        {'id': 1, 'name': '歌A', 'artists': '歌手X',
+         'album': '专辑Z', 'picUrl': 'https://pic/1.jpg'},
+        {'id': 2, 'name': '歌B', 'artists': '未知歌手',
+         'album': '未知专辑', 'picUrl': ''},
+    ]
+    assert 'incomplete' not in out
+    assert _batch_c_payloads(api_capture['calls']) == [[1, 2]]  # 缺 id 的 trackId 不进批次
+
+
+# ============ 批次容错 ============
+
+async def test_batch_business_failure_marked_incomplete(api_capture):
+    """明细批次业务失败：计 failed_batches，显式标 incomplete，不冒充完整。"""
+    api_capture['batch_resps'] = [_FakeResp({'code': 512, 'message': '爆了'})]
+    out = await _detail(api_capture, {'id': 1, 'trackIds': [{'id': 1}, {'id': 2}]})
+    assert out['tracks'] == []
+    assert out['incomplete'] is True
+    assert out['missing'] == 2
+    assert out['failed_batches'] == 1
+
+
+async def test_batch_non_dict_counts_as_failed(api_capture):
+    """批次响应体为 null（非 dict）：按失败批次计，不让 AttributeError 失真。"""
+    api_capture['batch_resps'] = [_FakeResp(None)]
+    out = await _detail(api_capture, {'id': 1, 'trackIds': [{'id': 9}]})
+    assert out['incomplete'] is True
+    assert out['missing'] == 1
+    assert out['failed_batches'] == 1
+
+
+async def test_dirty_trackid_skips_whole_batch_without_fail_count(api_capture):
+    """脏 ID（'①'.isdigit() 为真但 int() 抛 ValueError）：跳过整批且不计失败批次。"""
+    api_capture['batch_resps'] = []  # 不应有批次请求发出
+    out = await _detail(api_capture, {'id': 1, 'trackIds': [{'id': '①'}]})
+    assert out['tracks'] == []
+    assert out['incomplete'] is True
+    assert out['missing'] == 1
+    assert out['failed_batches'] == 0
+    assert _batch_c_payloads(api_capture['calls']) == []
+
+
+async def test_empty_trackids_no_batch_no_incomplete(api_capture):
+    """trackIds 为空：不发生批次请求，结果完整。"""
+    out = await _detail(api_capture, {'id': 1, 'trackIds': []})
+    assert out['tracks'] == []
+    assert 'incomplete' not in out
+    assert _batch_c_payloads(api_capture['calls']) == []
+
+
+async def test_batches_of_100(api_capture):
+    """101 首分两批：首批 100、次批 1。"""
+    api_capture['batch_resps'] = [
+        _FakeResp({'code': 200, 'songs': []}),
+        _FakeResp({'code': 200, 'songs': []}),
+    ]
+    track_ids = [{'id': i} for i in range(1, 102)]
+    out = await _detail(api_capture, {'id': 1, 'trackIds': track_ids})
+    payloads = _batch_c_payloads(api_capture['calls'])
+    assert len(payloads) == 2
+    assert len(payloads[0]) == 100
+    assert payloads[1] == [101]
+    assert out['incomplete'] is True  # 明细一首未回，101 全缺
+    assert out['missing'] == 101
+
+
+# ============ 错误映射 ============
+
+async def test_network_error_maps_to_request_failed(api_capture, monkeypatch):
+    """网络层异常（含批次阶段的）：统一转「获取歌单详情请求失败」。"""
+
+    async def _boom(url: str, **kw: Any):
+        raise api_mod.requests.RequestException('connection reset')
+
+    monkeypatch.setattr(api_mod.requests, 'post', _boom)
+    with pytest.raises(APIException, match='获取歌单详情请求失败'):
+        await _API.get_playlist_detail(123, {})
+
+
+async def test_json_decode_error_maps_to_parse_failed(api_capture):
+    api_capture['playlist_resp'] = _FakeResp(json_error=json.JSONDecodeError('bad', 'x', 0))
+    with pytest.raises(APIException, match='解析歌单详情响应失败'):
+        await _API.get_playlist_detail(123, {})