MuJoCo

A plausible render proves little by itself. Follow the physical chain from model through kinematics, actuation, contact, and observation.

Start from the model

For a first interactive tryout, new app, or first policy demo, read architect before creating a scene, controller, or viewer or downloading a model collection. Reuse its compatible reference-app selection if already made. Existing-model edits, physics debugging, and explanations stay here.
Read the MJCF and the pinned asset revision before adding control code. Check joint ranges, actuator limits, collision geometry, sites, masses, and the intended work surface.
Prefer a maintained model from MuJoCo Menagerie, but verify it against the real robot and task envelope.
Confirm gripper polarity, fingertip gap, and contact geometry empirically. Names and documentation can disagree with the model that actually runs.
Use the current MuJoCo documentation for MJCF and Python APIs rather than carrying signatures forward from memory.

Kinematics: solve only for reachable targets and check the residual; damped least-squares can return a poor local solution without raising.
Actuation: compare commanded position or torque with joint state, actuator force, range limits, and saturation.
Contact: inspect which geoms belong to the gripper and object. Unnamed mesh geoms make name-only contact filters unsafe.
Grasp: calibrate the grasp point, approach path, wrist orientation, and lift together. The end-effector site is not automatically the physical pinch point.
Observation: make cameras and renderer lifecycle deterministic before using frames as training or regression data.
Controls: distinguish model state, actuator limits, and rounded UI ranges. Clamp reset values to the actual widget bounds before binding them; a physically valid state can still be rejected by a narrower control.

For reachability, collision, grasp, saturation, and rendering symptoms, read FAILURES.md.
For the measured SO-arm and macOS evidence from Robium's manipulation trial, read SO-ARM-MACOS.md. Preserve its numbers only with the stated model, scene, hardware, and renderer conditions.
Use LeRobot guidance when the boundary reaches datasets, policies, or evaluation; use simulator-selection guidance when MuJoCo itself has not yet been chosen.

The intended workspace is reachable, commands produce the expected joint and contact state, grasps survive a lift across representative poses, and seeded resets produce acceptably stable observations.