fix(fam-edge): 生产者扫描跳过已被 DiskGuard 清理的文件

生产者列目录之后、读 mtime 之前，DiskGuard 可能刚好把那个文件删了（两个后台线程
的正常竞态），os.path.getmtime 抛 FileNotFoundError。代价不是少处理一个文件，而是
**整轮扫描中断**——排在后面的新素材本轮全都登记不上，要等下一轮。

线上日志：生产者扫描异常: [Errno 2] No such file or directory:
/opt/fam-edge/gdrive_videos/20260911PM/Generic_ONVIF-001-20260911-234730-...mp4
（01:30:01 抛出，同一秒 DiskGuard 正在清理那批文件）

改成捕获 OSError 跳过该文件继续扫。新增 tests/test_video_queue.py：被删的跳过且
后面的照常登记、仍在写入的（mtime 太新）依然跳过。

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

fam-edge/tests/test_video_queue.py

@@ -0,0 +1,73 @@
+"""VideoQueue 生产者扫描的单测。
+
+目前只覆盖一个点：生产者列目录之后、读 mtime 之前，DiskGuard 可能刚好把文件清掉
+（两个后台线程的正常竞态）。线上表现为 `生产者扫描异常: [Errno 2] No such file or
+directory`，代价是**整轮扫描中断**——排在后面的新素材本轮全都登记不上，要等下一轮。
+"""
+import os
+
+import pytest
+
+from fam_edge import video_queue as vq_mod
+from fam_edge.video_queue import VideoQueue
+
+
+class _FakeDB:
+    """只实现生产者路径上用到的方法。"""
+    def __init__(self):
+        self.registered = []
+        self.activities = []
+
+    def get_video_by_filename(self, fn):
+        return None
+
+    def ensure_video(self, fn, path, camera_name=None):
+        self.registered.append(fn)
+        return len(self.registered)
+
+    def set_video_file_status(self, vid, valid, err, meta=None):
+        pass
+
+    def record_activity(self, service, action, detail=''):
+        self.activities.append((service, action))
+
+
+@pytest.fixture
+def queue_with_two_files(tmp_path, monkeypatch):
+    monkeypatch.setattr(vq_mod, 'load_config', lambda: {
+        'gdrive_sync': {'local_dir': str(tmp_path), 'camera_name': '客厅'},
+        'video_processing': {'file_validate': True, 'stable_window_sec': 60},
+    })
+    (tmp_path / "a_被删掉的.mp4").write_bytes(b"x")
+    (tmp_path / "b_正常的.mp4").write_bytes(b"y")
+    db = _FakeDB()
+    q = VideoQueue(db)
+    monkeypatch.setattr(q, '_enqueue', lambda vid: None)
+    monkeypatch.setattr(vq_mod, 'validate_video', lambda p: (True, '', {'fps': 25}))
+    return q, db
+
+
+def test_produce_skips_file_deleted_mid_scan_and_keeps_going(queue_with_two_files, monkeypatch):
+    """被删掉的那个跳过，后面的照常登记——不能整轮中断。"""
+    q, db = queue_with_two_files
+    real_getmtime = os.path.getmtime
+
+    def fake_getmtime(path):
+        if 'a_被删掉的' in path:
+            raise FileNotFoundError(2, 'No such file or directory', path)
+        return real_getmtime(path) - 3600      # 早于稳定窗口，视为写入完成
+    monkeypatch.setattr(vq_mod.os.path, 'getmtime', fake_getmtime)
+
+    q._produce_once()                          # 不抛异常
+
+    assert db.registered == ["b_正常的.mp4"]   # 被删的跳过，后面的没受影响
+
+
+def test_produce_still_skips_files_being_written(queue_with_two_files, monkeypatch):
+    """mtime 太新（rclone 还在写）仍然要跳过，别把半成品入队。"""
+    q, db = queue_with_two_files
+    monkeypatch.setattr(vq_mod.os.path, 'getmtime', lambda p: __import__('time').time())
+
+    q._produce_once()
+
+    assert db.registered == []