Verbatim UpdatePhysicsInternal (0x00510700): the small-velocity-zero
(<0.25 m/s) fires unconditionally, not gated on OnWalkable (the old acdream
divergence) — gravity re-accelerates the same frame via the unconditional
v += a*dt. Adds TransientStateFlags.Stationary{Fall,Stop,Stuck} (0x10/0x20/0x40)
for the fsf round-trip, plus PhysicsBody.FramesStationaryFall and the separate
CachedVelocity field (retail's two-velocity model — reporting/DR only, never fed
to the integrator). All 1536 physics tests green.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
6e8117741b