[Newton] Avoid repeated model startup work

[ooctipus]

Summary

This is the model/articulation part of the scoped Newton startup work. It keeps startup work with the component that owns it:

• each Newton manager declares only the custom builder schema used by its active solver;
• articulation target modes are resolved for the prototype and copied to its replicas;
• the base physics manager owns the articulation-view registry;
• articulations create and register their view, while joint-wrench sensors reuse it or create it when used independently;
• root expressions remain regular expressions instead of taking a lossy regex-to-glob round trip.

The active-solver and reusable-view findings originated in Chris's #7269. This PR isolates those model/articulation changes so #7269 can remain the contact/raycast change under Chris's PR.

This replaces the cloner's unconditional MuJoCo + Kamino registration and the duplicate joint-wrench view. There is no view scan, manager-specific cache API, compatibility fallback, or duplicate registry.

The production diff against the current base is +57/-60 (net -3).

The explicit-global-ownership part is #7292. The contact/raycast part remains in #7269.

Startup benchmark

RTX 5090, CUDA device 1, 4096 environments, three fresh processes per revision/task. Values are median end-to-end startup wall time; raw runs are included below. Base: 86cf66651bd. PR: 947869af173.

Task	Base	PR	Change
Isaac-Cartpole	8.316 s	7.655 s	-8.0%
Isaac-Velocity-Rough-UnitreeGo2	17.525 s	14.844 s	-15.3%
Isaac-Lift-KukaAllegro-Camera	41.691 s	36.832 s	-11.7%

Raw totals:

• Cartpole base: 10.595, 8.190, 8.316 s; PR: 7.655, 7.674, 7.469 s.
• Go2 rough base: 17.568, 17.525, 16.426 s; PR: 14.852, 14.844, 14.724 s.
• Kuka camera base: 47.590, 41.691, 38.724 s; PR: 36.832, 36.666, 37.032 s.

The measured env_creation medians improve from 6.473 to 5.801 s for Cartpole, 15.558 to 12.863 s for Go2 rough, and 37.481 to 32.578 s for Kuka camera.

Test plan

• 247 passed across the physics-manager lifecycle, Newton cloner, manager abstraction, coupled-manager, and joint-wrench reuse tests.
• test_rename_builder_labels.py: 17 passed after removing obsolete solver-registration mocks.
• Ruff check and format pass on all changed Python files.
• The three 4096-environment benchmark tasks provide end-to-end Newton MJWarp startup coverage.

[isaaclab-review-bot]

Isaac Lab Review Bot

The PR appropriately moves solver-specific builder registration to Newton managers, memoizes articulation target-mode resolution, and centralizes articulation-view ownership. One compatibility issue remains: get_physics_sim_view() no longer provides its previously documented mutable registration list.

• Design and architecture: Builder-schema ownership is cleanly moved out of the cloner and into active solver managers, while articulation views are canonicalized by exact root expression. However, replacing the existing view registry with snapshots changes how external assets can register views.
• API: get_physics_sim_view() previously returned the live registry and explicitly supported get_physics_sim_view().append(view). It now returns a newly allocated list, so existing callers can append without error but their views are not registered. Preserve append-compatible behavior or introduce an explicit registration API with a deprecation and migration path.
• Implementation: The target-mode cache includes DOF names and imported stiffness and damping values, then reapplies modes using local indices. The canonical articulation-view cache is reset by clear(), and the updated articulation and joint-wrench paths use it. The remaining implementation concern is the snapshot returned by get_physics_sim_view(), which silently discards mutations expected by its prior contract.

Minor fixes needed. Posted 1 actionable finding inline.

Automated review; human maintainers own approval decisions.

[isaaclab-review-bot]

🟡 Warning · Api — get_physics_sim_view no longer accepts registrations

This method previously returned the live _views registry and documented that assets append their views so sensors can find them (as Articulation._initialize_impl did). It now returns list(cls._articulation_views.values()), a per-call snapshot, so any remaining or extension-side get_physics_sim_view().append(view) silently registers nothing and non-articulation views become undiscoverable with no error. Add an explicit registration classmethod, or keep append-compatible semantics with a deprecation path.

[greptile-apps]

Greptile Summary

This PR moves Newton builder-schema registration to the active solver managers and reduces repeated articulation startup work.

• Registers MuJoCo and Kamino custom attributes only when their managers are active, while coupled managers delegate setup to configured child solvers.
• Caches actuator target-mode resolution for structurally identical articulation clones.
• Canonicalizes articulation views by exact root expression so articulations and joint-wrench sensors share one view.
• Preserves regular-expression root selectors instead of converting them through glob syntax.

Confidence Score: 5/5

The PR appears safe to merge, with no concrete blocking or independently actionable non-blocking issue established.

The changed startup paths consistently delegate schema registration to active solver managers, reuse articulation setup by exact expression or structural signature, and retain regression coverage for the affected contracts.

Important Files Changed

Filename	Overview
source/isaaclab_newton/isaaclab_newton/physics/newton_manager.py	Adds active-solver schema registration and a root-expression-keyed articulation-view registry; no publishable defect was established.
source/isaaclab_newton/isaaclab_newton/assets/articulation/articulation.py	Reuses actuator-mode resolution across identical clone signatures and obtains the canonical manager-owned articulation view.
source/isaaclab_newton/isaaclab_newton/sensors/joint_wrench/joint_wrench_sensor.py	Reuses the manager-owned articulation view instead of constructing a duplicate sensor-specific view.
source/isaaclab_newton/isaaclab_newton/cloner/newton_clone_utils.py	Removes unconditional MuJoCo and Kamino schema registration from generic clone-source construction.
source/isaaclab_contrib/isaaclab_contrib/coupling/coupler.py	Delegates builder registration and finalization preparation to every configured child solver manager.
source/isaaclab_contrib/isaaclab_contrib/custom_coupling/coupled_mjwarp_vbd_manager.py	Declares MuJoCo as the custom coupled manager's builder-attribute owner.

Sequence Diagram

sequenceDiagram
    participant Scene as Scene startup
    participant Manager as Active Newton manager
    participant Builder as ModelBuilder
    participant Asset as Articulation
    participant Cache as Articulation-view cache
    participant Sensor as Joint-wrench sensor
    Scene->>Manager: create_builder()
    Manager->>Builder: register active solver attributes
    Scene->>Builder: import and finalize model
    Asset->>Manager: get_articulation_view(root expression)
    Manager->>Cache: create or reuse canonical view
    Cache-->>Asset: shared ArticulationView
    Sensor->>Manager: get_articulation_view(same expression)
    Cache-->>Sensor: same ArticulationView

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