test: captured frames do not share memory with the SDK frame

The fake frames now hand out a buffer (memoryview) like pyrealsense2's
BufData, so np.asanyarray() of it is a view, as on the robot; a control test
proves it. Then: the captured rgb/depth share no memory with the fake SDK
frame and own their data (without the fix both shared it), and _owned()
copies views only.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/test_frame_copy.py

@@ -0,0 +1,39 @@
+"""Frames acquired from the pipeline own their memory: nothing points into the SDK's buffers."""
+
+import numpy as np
+import pytest
+
+pytest.importorskip("pyrealsense2")
+
+from src.backend.services.camera import RealSenseD435, _owned  # noqa: E402
+from tests.fake_realsense import FakeFrameset, FakePipeline, open_fake_camera  # noqa: E402
+
+
+def test_the_fake_hands_out_views_like_the_sdk():
+    """Control: without the copy, the driver's arrays WOULD share the SDK frame's memory."""
+    color = FakeFrameset(1).get_color_frame()
+    assert np.shares_memory(np.asanyarray(color.get_data()), color.array)
+
+
+def test_captured_frame_does_not_share_memory_with_the_sdk_frame():
+    cam = RealSenseD435()
+    pipe = FakePipeline()
+    open_fake_camera(cam, pipe)
+    try:
+        frame = cam.capture()
+        sdk = pipe.last_frameset
+        assert frame is not None
+        assert not np.shares_memory(frame.rgb, sdk.get_color_frame().array)
+        assert not np.shares_memory(frame.depth, sdk.get_depth_frame().array)
+        assert frame.rgb.base is None and frame.depth.base is None
+        np.testing.assert_array_equal(frame.rgb, sdk.get_color_frame().array)   # same pixels
+    finally:
+        cam.close()
+
+
+def test_owned_copies_views_only():
+    owned = np.zeros((4, 4), np.uint16)
+    view = np.asanyarray(memoryview(owned))
+    assert _owned(owned) is owned
+    copy = _owned(view)
+    assert copy is not view and not np.shares_memory(copy, owned)