## What changed

<!-- Summarize the change: files/functions touched and the user-facing effect. -->

## Why

<!-- Root cause or rationale. Link related issues with "Closes #123". -->

## Validation

<!-- Commands run and what passed, for example: -->
<!-- - make format lint typecheck -->
<!-- - uv run pytest tests/mujoco/test_envs.py -q -->

## Checklist

- [ ] Tests added or updated (regression test for a fix; happy path plus an edge case for new behavior).
- [ ] `make format lint typecheck` and the relevant tests pass locally.
- [ ] Documentation updated if the public API or behavior changed.
- [ ] `CHANGELOG.md` `## [Unreleased]` entry added for any user-facing change.
- [ ] No em dashes or emoji in prose, docs, or comments.
