- Vec3.lerp(other, t) for linear interpolation between two points
- ParticleTrail.sample(from, to, density) emits density-based interpolated
points strictly between endpoints (endpoints excluded by construction)
- TRAIL_DENSITY = 4.0 particles per block
- 6 ParticleTrail tests + 3 Vec3.lerp tests, all green
- Zero Hytale imports — chain/ frontier preserved
