支持主机桥接后固定δt与旋转先验，并落盘运动对供可视化直读。

Co-authored-by: Cursor <cursoragent@cursor.com>

tests/test_motion_pairs_io.py

@@ -0,0 +1,55 @@
+"""Tests for motion-pair cache IO."""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+import numpy as np
+
+from imu_lidar.contracts import MotionPair
+from imu_lidar.motion_pairs_io import (
+    build_motion_pairs_payload,
+    load_motion_pairs,
+    pair_from_dict,
+    pair_to_dict,
+    pairs_for_session,
+    save_motion_pairs,
+)
+
+
+def test_pair_roundtrip(tmp_path: Path) -> None:
+    pair = MotionPair(
+        session_id="s0",
+        i=1,
+        j=4,
+        t_i_s=1.0,
+        t_j_s=2.5,
+        R_A=np.eye(3),
+        R_B=np.eye(3),
+        t_A_m=np.array([0.1, 0.0, 0.0]),
+        t_B_m=np.array([0.1, 0.0, 0.0]),
+        fitness=0.8,
+        metadata={"weight": 12.0, "cov9": [[0.0] * 9] * 9, "backend": "test"},
+    )
+    encoded = pair_to_dict(pair)
+    assert "cov9" not in encoded["metadata"]
+    assert encoded["metadata"]["weight"] == 12.0
+    restored = pair_from_dict(encoded)
+    assert restored.i == 1 and restored.j == 4
+    np.testing.assert_allclose(restored.t_A_m, [0.1, 0.0, 0.0])
+
+    payload = build_motion_pairs_payload(
+        prepared_sessions=[
+            {
+                "session_id": "s0",
+                "time_offset_s": 0.0,
+                "gyro_bias_rad_s": np.zeros(3),
+                "pairs": (pair,),
+            }
+        ]
+    )
+    path = save_motion_pairs(tmp_path / "motion_pairs.json", payload)
+    loaded = load_motion_pairs(path)
+    pairs = pairs_for_session(loaded, "s0")
+    assert len(pairs) == 1
+    assert pairs[0].session_id == "s0"