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>

imu_lidar/time_offset.py

@@ -190,6 +190,7 @@ def refine_time_offset_signed(
     gyro_bias_rad_s: np.ndarray | None = None,
     search_s: float = 0.08,
     sample_hz: float = 50.0,
+    max_shift_s: float | None = 0.05,
 ) -> TimeOffsetResult:
     """Refine ``δt`` with signed 3-axis rates using a known ``R_IMU_lidar``.
 
@@ -293,9 +294,23 @@ def refine_time_offset_signed(
         f"corr={best_corr:.3f}, mag_corr={mag_at_best:.3f} (coarse_mag={mag_at_coarse:.3f}), "
         f"search=±{half:.3f}s"
     )
+    shift = abs(best_delta - float(delta_t_s))
+    if max_shift_s is not None and shift > float(max_shift_s):
+        notes.append(
+            f"signed refine rejected: |Δδt|={shift:.4f}s exceeds max_shift={float(max_shift_s):.4f}s; "
+            "keeping previous delta_t"
+        )
+        return TimeOffsetResult(
+            delta_t_s=float(delta_t_s),
+            correlation_peak=mag_at_coarse if mag_at_coarse > 0 else best_corr,
+            search_s=search_s,
+            notes=tuple(notes),
+            ok=True,
+        )
+    # Require a meaningful MSE drop so tiny downhill noise cannot walk δt across iterations.
     improved = (
         np.isfinite(best_cost)
-        and best_cost < coarse_cost * 0.999
+        and best_cost < coarse_cost * 0.98
         # Do not sacrifice the more reliable magnitude alignment for a noisy signed MSE gain.
         and mag_at_best + 1e-4 >= mag_at_coarse
     )