PyBullet saveWorld resurrects a removed object after body-ID reuse

Environment

• OS: Ubuntu 24.04.5 LTS, Linux 7.0.0-28-generic x86_64
• Compiler: GCC 11.5.0
• Python: 3.12.3
• Source: bulletphysics/bullet3 master at 63c4d67e337017f9d8b298c900e9aabdb69296e7
• PyBullet: built locally from that exact checkout

Description

PyBullet records imported filenames and body IDs in m_saveWorldBodyData. removeBody frees the body handle but leaves its ID in that serialization metadata. When a later object reuses the ID, saveWorld resolves the stale record through the replacement and serializes both assets at the replacement's pose.

Expected behavior: saveWorld emits only objects that are live at save time.

Actual behavior: the reproducer loads cube.urdf as body 0, removes it, and loads sphere2.urdf at x=5 as reused body 0. The saved program contains both a cube load and a sphere load, each at x=5. Replaying it therefore resurrects the deleted cube.

Sources:

• metadata creation: https://github.com/bulletphysics/bullet3/blob/63c4d67e337017f9d8b298c900e9aabdb69296e7/examples/SharedMemory/PhysicsServerCommandProcessor.cpp#L3198-L3230
• serialization: https://github.com/bulletphysics/bullet3/blob/63c4d67e337017f9d8b298c900e9aabdb69296e7/examples/SharedMemory/PhysicsServerCommandProcessor.cpp#L4389-L4465
• removal: https://github.com/bulletphysics/bullet3/blob/63c4d67e337017f9d8b298c900e9aabdb69296e7/examples/SharedMemory/PhysicsServerCommandProcessor.cpp#L12739-L12947

Reproduction package:

save-world-removed-body-id-poc.zip

Steps to reproduce

1. Build PyBullet from the commit above using poc/README.md.
2. Run python poc/reproducer.py.
3. Inspect the printed loadURDF lines and the generated saved_world.py.

Observed output is in poc/observed-output.txt.