PhysicsSystem had 940 lines. The step logic shares its state with the engine handles of parts and bodies, so a separate class would need almost the whole system as its interface. That part stays. Two pieces without own state move out instead. Behaviour is unchanged. - passesOneWay in oneWay.ts is the one-way rule as a pure function. It can now be tested without Rapier. - bodyGeometry.ts holds the collider shapes and the pose maths. - PhysicsSystem is down to 820 lines. Tests: - ./check.sh: 146 files, 2199 tests, CHECK EXIT 0 - 5 new unit tests for the one-way rule without an engine. - New tests/core/body-geometry.test.ts: a capsule turned by 90 degrees went unnoticed before. Both tests fail against that bend. - Counter-checks on landing hold and teleport detection fail in 3 to 6 tests each. - e2e 1-28,31,36,39-43 on the final state: ALL PASSED, 1060 checks - Each of the four #215 commits was checked green on its own in a scratch worktree: 2190, 2192, 2192, 2199 tests. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>