fix(viz): numpy-safe hand filter + tests

- _emit_hands: replace bare `if h` with numpy-safe predicate
  `h is not None and len(h) > 0` in single-person fallback
- test_hand_features: add numpy-row landmark test for
  HandFeatureExtractor.step(), asserting finite cx/cy/openness
- test_action_head_pub: add fallback-path test and two-pid
  once-per-tick invariant test for send_hands

data_only_viz/action_head_pub.py

@@ -153,7 +153,7 @@ class ActionHeadPublisher(threading.Thread):
             if not hands and getattr(self.state, "hands_present", False):
                 lkp = getattr(self.state, "left_hand_kp", None)
                 rkp = getattr(self.state, "right_hand_kp", None)
-                hands = [h for h in (lkp, rkp) if h]
+                hands = [h for h in (lkp, rkp) if h is not None and len(h) > 0]
         feats = self._hand_ext.step(hands)
         self.bridge.send_hands(feats, t_now)
 

data_only_viz/tests/test_action_head_pub.py

@@ -207,3 +207,36 @@ def test_emit_hands_called_once_per_tick_empty() -> None:
     assert feats["L"] is None
     assert feats["R"] is None
     assert feats["dist"] == 0.0
+
+
+def test_emit_hands_single_person_fallback_sends_once() -> None:
+    """Single-person fallback (hands_present=True + left/right_hand_kp) → send_hands once."""
+    from data_only_viz.action_head_pub import ActionHeadPublisher
+    state = _FakeState()
+    bridge = MagicMock()
+    pub = ActionHeadPublisher(state, bridge, ckpt_path=None)
+
+    # No per-person hands list; exercise the single-person fallback branch.
+    state.persons_hands = []
+    state.hands_present = True
+    state.left_hand_kp = _fake_hand_21(0)
+    state.right_hand_kp = _fake_hand_21(1)
+    state.persons_smplx = [_make_smplx_person(0)]
+    state.smplx_last_t = 1.0
+    pub._tick(t_now=0.0)
+
+    bridge.send_hands.assert_called_once()
+
+
+def test_emit_hands_once_for_two_pids() -> None:
+    """Two pids in persons_smplx → send_hands called exactly once, not once per pid."""
+    from data_only_viz.action_head_pub import ActionHeadPublisher
+    state = _FakeState()
+    bridge = MagicMock()
+    pub = ActionHeadPublisher(state, bridge, ckpt_path=None)
+
+    state.persons_smplx = [_make_smplx_person(0), _make_smplx_person(1)]
+    state.smplx_last_t = 1.0
+    pub._tick(t_now=0.0)
+
+    assert bridge.send_hands.call_count == 1

data_only_viz/tests/test_hand_features.py

@@ -80,3 +80,23 @@ def test_nan_landmark_falls_back_no_exception():
     out = ext.step([h])           # must not raise
     hand = out["L"] or out["R"]
     assert math.isfinite(hand["cx"]) and math.isfinite(hand["openness"])
+
+
+def test_numpy_row_landmarks_finite_features():
+    """Landmarks as numpy rows (indexable [x, y, ...]) must yield finite cx/cy/openness."""
+    import numpy as np
+    arr = np.zeros((21, 3), dtype=np.float32)
+    # replicate _hand(0.5, 0.5, span=0.20) geometry via index access
+    arr[:] = [0.5, 0.5, 0.0]
+    arr[0] = [0.5, 0.55, 0.0]   # wrist
+    arr[9] = [0.5, 0.45, 0.0]   # middle_mcp → size 0.10
+    arr[4] = [0.4, 0.5, 0.0]    # thumb_tip
+    arr[20] = [0.6, 0.5, 0.0]   # pinky_tip → span 0.20
+    ext = HandFeatureExtractor()
+    out = ext.step([arr])        # must not raise
+    hand = out["L"] or out["R"]
+    assert hand is not None
+    assert math.isfinite(hand["cx"])
+    assert math.isfinite(hand["cy"])
+    assert math.isfinite(hand["openness"])
+    assert hand["openness"] > 0.8  # span/size = 2.0, same as test_open_hand