fix(pybot): 录制时改用同步 capture() 按需抓帧，避免帧重复

_grab_frame 从 camera.latest()（读后台队列）改为 camera.capture()
（直接调 grabber 同步抓帧），确保每个微动作拿到独立帧而非队列中
可能重复的旧帧。Camera 新增 capture() 方法。

pybot/pybot/hd/camera.py

@@ -69,6 +69,12 @@ class Camera:
         with self._lock:
             return self._queue[-1] if self._queue else None
 
+    def capture(self):
+        """同步抓一帧（按需，不从队列读）；dry_run 或无 grabber 返回 None"""
+        if self._grabber is None:
+            return None
+        return self._grabber()
+
     def snapshot(self):
         """队列快照 list（旧→新），供消费方批量取帧"""
         with self._lock:

pybot/pybot/robot.py

@@ -254,13 +254,13 @@ class RobotStruct:
         return vec
 
     def _grab_frame(self, camera_var):
-        """从摄像头取最新帧；dry_run 或无帧时返回随机噪声帧"""
+        """从摄像头同步抓一帧；dry_run 或无帧时返回随机噪声帧"""
         import numpy as np
         if camera_var is not None:
-            result = camera_var.play({})
-            if result is not None:
-                return result[1]       # (timestamp, frame)
-        # dry_run 或队列空：随机噪声帧（用 camera 配置尺寸）
+            frame = camera_var.camera.capture()
+            if frame is not None:
+                return frame
+        # dry_run 或无 grabber：随机噪声帧（用 camera 配置尺寸）
         h, w = 480, 640
         if camera_var is not None:
             cam = camera_var.camera

pybot/tests/test_camera.py

@@ -82,6 +82,20 @@ def test_dry_run_no_hardware():
     assert cam.latest() is None
 
 
+def test_capture_on_demand():
+    """capture() 同步按需抓帧，每个微步一帧"""
+    cam = Camera(grabber=FakeGrabber())
+    assert cam.capture() == 1
+    assert cam.capture() == 2       # 每次调用递增，不复用队列
+    assert cam.capture() == 3
+
+
+def test_capture_no_grabber():
+    """dry_run 或未 setup 时 capture() 返回 None"""
+    cam = Camera(dry_run=True)
+    assert cam.capture() is None
+
+
 def test_camera_var_from_matrix():
     robot = RobotStruct(CAMERA_MT, dry_run=True)
     cam = robot.M["cam0"].camera