feat(unitree_g1): hold neutral SONIC token until first command

Move the token-hold idle logic into SonicWholeBodyController via a
token_mode flag (set by UnitreeG1 when sonic_token_action is enabled):
before any real token arrives the decoder is fed the all-zero neutral
token (stable neutral stance), and afterwards the last received token is
held between control ticks (the ~50 Hz control loop outruns the ~30 Hz
token stream). Living in the controller, this applies uniformly to
run_g1_onboard, lerobot-rollout and the sim replays, so the explicit
neutral seeding in run_g1_onboard is removed.

src/lerobot/robots/unitree_g1/controllers/sonic_whole_body.py

@@ -229,6 +229,17 @@ class SonicWholeBodyController:
         # forwarded to the pipeline as ``delta_heading`` so turn commands take effect.
         self._heading = 0.0
 
+        # Token-interface state. ``token_mode`` is set True by the robot when the deploy
+        # is token-driven (``UnitreeG1Config.sonic_token_action``): the controller then
+        # holds a stable *neutral* (all-zero) token until the first real token arrives,
+        # and afterwards holds the *last* token received between ticks (the async
+        # controller runs ~50 Hz while a token VLA streams ~30 Hz). This lives here (not
+        # in the entry-point script) so it applies uniformly to run_g1_onboard,
+        # lerobot-rollout and the sim replays. ``token_mode`` stays False for the dense
+        # 34-D whole-body / OpenHLM path, which keeps its own "hold last target" idle.
+        self.token_mode = False
+        self._last_token: np.ndarray | None = None
+
         logger.info("SONIC ready (encoder/decoder, 34-D whole-body command path)")
 
     def _run_wholebody34(self, obs: dict, wb: np.ndarray) -> dict:
@@ -346,7 +357,15 @@ class SonicWholeBodyController:
         # Checked before the joint path so a token action takes precedence.
         token = _extract_token_from_action(action)
         if token is not None:
-            return self._startup_blend(obs, self._run_token(obs, token))
+            self._last_token = token
+        elif self._last_token is None and self.token_mode:
+            # Token-driven deploy, but no token has arrived yet: hold the neutral
+            # (all-zero) token, which the decoder maps to a stable neutral stance.
+            self._last_token = np.zeros(TOKEN_DIM, dtype=np.float32)
+        if self._last_token is not None:
+            # Either a fresh token this tick or the last one received (held between the
+            # ~30 Hz token stream and the ~50 Hz control loop).
+            return self._startup_blend(obs, self._run_token(obs, self._last_token))
 
         # Dense 34-D whole-body command (OpenHLM / pi0.5 joint interface): a single
         # vector per tick drives the mode-0 encoder reference directly. Until the
@@ -372,6 +391,8 @@ class SonicWholeBodyController:
         self._wb_traj.clear()
         self._wb_quat_traj.clear()
         self._heading = 0.0
+        # Drop the held token so token_mode re-seeds the neutral token after a reset.
+        self._last_token = None
 
     def shutdown(self):
         self._runtime.shutdown()

src/lerobot/robots/unitree_g1/run_g1_onboard.py

@@ -139,6 +139,9 @@ def main() -> None:
     robot = UnitreeG1(cfg)
     logger.info("Connecting onboard robot (controller=%s, token=%s)...", args.controller, args.sonic_token_action)
     robot.connect()
+    # Note: with --sonic-token-action the SonicWholeBodyController holds a neutral
+    # (all-zero) token until the first laptop token arrives, then holds the last token
+    # between ticks -- see SonicWholeBodyController.token_mode (set from config).
 
     grippers: dict[str, Gripper] = {}
     if args.grippers:

src/lerobot/robots/unitree_g1/unitree_g1.py

@@ -169,6 +169,11 @@ class UnitreeG1(Robot):
         # Lower-body controller loaded dynamically
         self.controller: LocomotionController | None = make_locomotion_controller(config.controller)
 
+        # Token-driven deploy: let a SONIC controller hold a neutral token until the
+        # first real one arrives, then hold the last token between control ticks.
+        if config.sonic_token_action and hasattr(self.controller, "token_mode"):
+            self.controller.token_mode = True
+
         # Controller thread state
         self._controller_thread = None
         # When set, the controller loop stops publishing low commands so reset() can