Fix contact sensor activation for nested rigid bodies

[ooctipus]

Summary

• use get_all_matching_child_prims when activating PhysX contact report schemas
• continue matching rigid descendants under nested rigid-body trees instead of stopping at the first rigid body
• add regression coverage for nested rigid bodies receiving PhysxContactReportAPI

Testing

• ./isaaclab.sh -p -m pytest source/isaaclab/test/sim/test_schemas.py -k activate_contact_sensors_nested_rigid_bodies -q
• ./isaaclab.sh -p -m py_compile source/isaaclab/isaaclab/sim/schemas/schemas.py source/isaaclab/test/sim/test_schemas.py

Note

• Attempted ./isaaclab.sh -p -m pytest source/isaaclab_physx/test/sensors/test_contact_sensor.py -k contact_sensor_threshold -q, but collection failed because flaky is not installed in the local environment.

[greptile-apps]

Greptile Summary

This PR fixes activate_contact_sensors to correctly apply PhysxContactReportAPI to all rigid bodies in a nested hierarchy by replacing a hand-written BFS that stopped traversal at the first rigid body found with get_all_matching_child_prims, which continues into children of matched prims.

• schemas.py: Replaces the manual traversal (which skipped children of rigid bodies) with get_all_matching_child_prims, enabling activation for nested rigid-body trees. The num_contact_sensors counter is removed in favor of checking if not rigid_body_prims.
• test_schemas.py: Adds a new regression test that builds a 3-level nested rigid-body hierarchy (pelvis → left_hip → left_knee) and asserts all three prims receive PhysxRigidBodyAPI, PhysxContactReportAPI, and correct attribute values.

Confidence Score: 5/5

Safe to merge — the change is a targeted, well-scoped fix with a direct regression test.

The old manual traversal was deliberately stopping at rigid-body prims and never enqueuing their children, which is exactly the bug being fixed. The replacement get_all_matching_child_prims already used elsewhere in the same file always continues traversal past matched nodes, so nested rigid bodies are now discovered. The per-prim schema-application logic is untouched. The new test constructs the exact hierarchy that previously broke and asserts all three levels receive the correct schemas and attribute values.

No files require special attention.

Important Files Changed

Filename	Overview
source/isaaclab/isaaclab/sim/schemas/schemas.py	Replaces manual BFS with get_all_matching_child_prims; correctly traverses nested rigid-body trees. Import was already present. Logic for applying schemas per-prim is unchanged.
source/isaaclab/test/sim/test_schemas.py	Adds test_activate_contact_sensors_nested_rigid_bodies covering a 3-deep rigid-body chain; all required imports (UsdPhysics, pytest) are already present.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A["activate_contact_sensors(prim_path)"] --> B["Validate prim"]
    B --> C["get_all_matching_child_prims\n(predicate: HasAPI RigidBodyAPI)"]
    C --> D{Full BFS traversal\nof all descendants}
    D -->|prim matches| E["Add to output list\n+ continue into children"]
    D -->|prim doesn't match| F["Continue into children"]
    E --> D
    F --> D
    D -->|queue empty| G["rigid_body_prims list"]
    G -->|empty| H["Warning: no rigid bodies found"]
    G -->|not empty| I["For each rigid body prim"]
    I --> J["Ensure PhysxRigidBodyAPI\nsleepThreshold = 0.0"]
    J --> K["Ensure PhysxContactReportAPI\nthreshold = user value"]
    K --> I

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flowchart TD
    A["activate_contact_sensors(prim_path)"] --> B["Validate prim"]
    B --> C["get_all_matching_child_prims\n(predicate: HasAPI RigidBodyAPI)"]
    C --> D{Full BFS traversal\nof all descendants}
    D -->|prim matches| E["Add to output list\n+ continue into children"]
    D -->|prim doesn't match| F["Continue into children"]
    E --> D
    F --> D
    D -->|queue empty| G["rigid_body_prims list"]
    G -->|empty| H["Warning: no rigid bodies found"]
    G -->|not empty| I["For each rigid body prim"]
    I --> J["Ensure PhysxRigidBodyAPI\nsleepThreshold = 0.0"]
    J --> K["Ensure PhysxContactReportAPI\nthreshold = user value"]
    K --> I

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