SONIC fidelity TODO — gaps vs gear_sonic / C++ deploy

Remaining differences between this lerobot SONIC port and the original gear_sonic + gear_sonic_deploy/g1_deploy_onnx_ref reference. All three deployed encoder modes exist (0 locomotion, 1 three-point, 2 full-body SMPL); these are faithfulness gaps in how some pieces behave.

1. 3-point calibration & source (mode 1)

The original derives the 3 points from full-body joints and calibrates with ThreePointPose against live measured robot joints (reset_with_measured_q), plus neck→waist coupling. Our device path (head + controllers, fixed zero-q neutral) is an approximation.

Missing: measured-q recalibration + waist coupling.
Note: the body-source compute_3point path (needs PICO Motion Trackers) is already faithful.

2. Locomotion stick/speed mapping (#6)

gear_sonic's PlannerLoop uses a yaw-accumulator + mode-dependent speed curves (slow 0.1 + 0.5·mag, run 1.5 + 3·mag) with a facing-rotated movement vector. We reuse the keyboard-parity apply_joystick_axes (no speed-by-mode curve).

Also: PICO stick sign conventions untested (may need axis flips in pico_publisher).
Self-contained and sim-testable.

3. Mode-2 root motion

enable_smpl_root=False by default; the original feeds the SMPL root orientation into the anchor. Faithful only when enabled and the 30→50 Hz root trajectory is smoothed/ rate-matched (currently causes base-acceleration spikes → NaN QACC).

4. Start/stop handshake

C++ has WAIT_FOR_CONTROL (operator "start" gate) and a "stop" halt. We start policy immediately after the startup ramp — no explicit arm/e-stop state machine.

5. Startup ramp target

C++ InitControl ramps to default_angles; we ramp to the policy's live commanded pose. Deliberate (per request) — only a gap if exact C++ parity is wanted.

6. Hands / grippers

Original maps trigger/grip → Dex3 hand joints in modes 1 & 2 (simple gripping: thumb open, trigger>0.5 closes middle finger, run through a gripper IK solver). Our 29-DOF path has no hand control.

Hardware here: OpenArm grippers (not Dex3) — could be routed through the same trigger→open/close path, but needs the robot interface to expose/command the gripper actuators (they're separate from the 29-DOF body).

Not gaps (settled)

vr_5point_index — vestigial constant in policy_parameters.hpp, not a deployed encoder mode. Nothing to implement.
Action scaling, kp/kd, IsaacLab↔MuJoCo remaps, encoder cadence (encode ⅕ / decode 1×), per-mode replan intervals (0.1/0.2/1.0), 8-frame cross-fade blend — all faithful.
Graceful damped shutdown — intentional safety addition, keep.

Suggested priority

High (change how the robot moves under teleop): #1, #2.
Medium: #3, #4, #6 (grippers).
Low / intentional: #5.

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