test(viz): pin stabilizer defaults, fix seams

Detection v3 review follow-ups: pin hand_persist_grace/near_off/
hold_frames defaults; use the module-level route_hands (restores the
monkeypatch seam, drops the dead local alias); document the grace
count-inheritance window in the gate docstring.

data_only_viz/action_head_pub.py

@@ -243,8 +243,7 @@ class ActionHeadPublisher(threading.Thread):
         without going through _tick).
         """
         hands, chir, _, _ = self._pick_hands()
-        from data_only_viz.hand_slots import route_hands as _rh
-        raw = _rh(
+        raw = route_hands(
             hands, chir or None,
             swap=getattr(self, "_hand_swap_lr", False),
             near_min=0.0,

data_only_viz/hand_display.py

@@ -271,8 +271,11 @@ class HandPersistenceGate:
 
     Known limit: matching is greedy nearest-track — two hands crossing
     within `radius` can inherit each other's track (and a ghost appearing
-    exactly where a real hand just left inherits its count). Acceptable
-    for a display gate; do not reuse for gesture-state tracking.
+    exactly where a real hand just left inherits its count). Grace widens
+    that inheritance window to `grace` frames after the hand leaves, and a
+    ghost re-flashing at one spot every (grace+1)th frame can accumulate to
+    min_frames. Acceptable for a display gate; do not reuse for
+    gesture-state tracking.
     """
 
     def __init__(self, min_frames: int = 3, radius: float = 0.15, grace: int = 0) -> None:

data_only_viz/tests/test_config.py

@@ -66,6 +66,10 @@ def test_defaults_hand_display():
     assert cfg.hand_near_min == pytest.approx(0.10)
     assert cfg.arkit_bone_max == pytest.approx(0.5)
     assert cfg.arkit_full_skeleton is True
+    # detection v3 stabilizer knobs
+    assert cfg.hand_persist_grace == 2
+    assert cfg.hand_near_off == pytest.approx(0.08)
+    assert cfg.hand_hold_frames == 2
 
 
 def test_defaults_misc():