feat(core): port decompiled AC client physics — CollisionPrimitives + PhysicsBody
Two major C# ports from the decompiled retail AC client (acclient.exe):
1. CollisionPrimitives (9 functions, 26 tests):
- SphereIntersectsRay, RayPlaneIntersect, CalcNormal
- SphereIntersectsPoly, FindTimeOfCollision
- HitsWalkable, FindWalkableCollision
- SlideSphere, LandOnSphere
Ported from chunk_00530000.c functions FUN_005384e0 through FUN_0053a230.
Cross-referenced against ACE's Physics/ C# port for algorithm verification.
2. PhysicsBody (7 methods, 31 tests):
- update_object (top-level per-frame, sub-stepped at MaxQuantum=0.1)
- UpdatePhysicsInternal (Euler: pos += v*dt + 0.5*a*dt²)
- calc_acceleration (gravity=-9.8 when HasGravity)
- set_velocity (clamp to MaxVelocity=50)
- set_local_velocity (body→world via quaternion)
- set_on_walkable, calc_friction (ground normal + pow decay)
Ported from chunk_00510000.c/chunk_00500000.c.
Struct layout confirmed against ACE PhysicsObj field offsets.
367 total tests green (258 core + 109 net). 57 new tests.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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