feat(iphone): store topology + 2d validity

Add arkit_joint_names, arkit_parents, persons_arkit_2d_valid
to State. Wire TAG_TOPOLOGY=7 dispatch in IphoneUSBSource:
decode_topology stored under lock; TAG_SKELETON2D branch now
also stores per-joint validity bool array (91,) alongside pts.

data_only_viz/iphone_usb_source.py

@@ -21,10 +21,12 @@ from data_only_viz.scripts.iphone_usb_bridge import (
     connect_device, decode_skeleton, decode_skeleton2D,
     iter_frames, TAG_SKELETON, TAG_SKELETON2D,
 )
+from data_only_viz.arkit_topology import decode_topology
 from data_only_viz.state import PoseKp
 
 TAG_VIDEO = 2
 TAG_HANDS = 4
+TAG_TOPOLOGY = 7
 LOG = logging.getLogger("iphone_usb_source")
 
 _HAND_BYTES = 1 + 21 * 12   # chirality:u8 + 21 × (x,y,z) × 4 bytes BE f32
@@ -152,10 +154,22 @@ class IphoneUSBSource:
                     elif tag == TAG_SKELETON2D and self.state is not None:
                         pts = decode_skeleton2D(payload)
                         if pts is not None:
-                            arr = np.array([[x, y] for (x, y, _v) in pts], dtype=np.float32)
+                            arr = np.array([[x, y] for (x, y, _v) in pts],
+                                           dtype=np.float32)
+                            valid = np.array([v for (_x, _y, v) in pts],
+                                             dtype=bool)
                             with self.state.lock():
                                 self.state.persons_arkit_2d[pid] = arr
-                                self.state.persons_arkit_2d_t[pid] = time.perf_counter()
+                                self.state.persons_arkit_2d_valid[pid] = valid
+                                self.state.persons_arkit_2d_t[pid] = \
+                                    time.perf_counter()
+                    elif tag == TAG_TOPOLOGY and self.state is not None:
+                        topo = decode_topology(payload)
+                        if topo is not None:
+                            names, parents = topo
+                            with self.state.lock():
+                                self.state.arkit_joint_names = names
+                                self.state.arkit_parents = parents
                     elif tag == TAG_HANDS:
                         hands = _decode_hands(payload)
                         if hands is not None and self.state is not None:

data_only_viz/state.py

@@ -148,6 +148,9 @@ class State:
     # screen coords 0..1) per pid. Updated by IphoneUSBSource on TAG_SKELETON2D.
     persons_arkit_2d: dict[int, "np.ndarray"] = field(default_factory=dict)
     persons_arkit_2d_t: dict[int, float] = field(default_factory=dict)
+    persons_arkit_2d_valid: dict = field(default_factory=dict)
+    arkit_joint_names: list = field(default_factory=list)
+    arkit_parents: list = field(default_factory=list)
 
     # ---- LiDAR / ICP mesh fusion (Task 8 - 2026-05-14) ----
     # Set by the LidarTCPReader poller; consumed by FusionWorker.run_once.

data_only_viz/tests/test_arkit_topology_state.py

@@ -0,0 +1,14 @@
+"""State carries ARKit topology + 2D validity for the renderer."""
+from data_only_viz.state import State
+
+
+def test_state_has_topology_fields():
+    s = State()
+    assert s.arkit_joint_names == []
+    assert s.arkit_parents == []
+    assert s.persons_arkit_2d_valid == {}
+
+
+def test_topology_tag_constant():
+    from data_only_viz.iphone_usb_source import TAG_TOPOLOGY
+    assert TAG_TOPOLOGY == 7