Initial commit: RegionIO Minecraft server core (26.1.2/protocol 775)

Vanilla-faithful overworld generator (final_density + multi-noise biomes),
full connection lifecycle (status/login/configuration/play), chunk streaming,
creative block editing, and the protocol/nbt/registry infrastructure.

internal/worldgen/randomstate.go

@@ -0,0 +1,34 @@
+package worldgen
+
+// RandomState seeds all worldgen noises from the world seed, mirroring the
+// vanilla RandomState: a positional factory derived from XoroshiroRandomSource
+// (overworld uses the non-legacy source), with each noise seeded by the MD5
+// hash of its resource location.
+type RandomState struct {
+	factory PositionalRandomFactory
+	noises  map[string]*NormalNoise
+}
+
+// NewRandomState builds the seeding context for the given world seed.
+func NewRandomState(seed int64) *RandomState {
+	return &RandomState{
+		factory: NewXoroshiro(seed).ForkPositional(),
+		noises:  make(map[string]*NormalNoise),
+	}
+}
+
+// Noise returns the NormalNoise for the named noise parameters, seeded as
+// NormalNoise.create(factory.fromHashOf(name), params) and cached.
+func (rs *RandomState) Noise(name string, firstOctave int, amplitudes []float64) *NormalNoise {
+	if n, ok := rs.noises[name]; ok {
+		return n
+	}
+	n := NewNormalNoise(rs.factory.FromHashOf(name), firstOctave, amplitudes)
+	rs.noises[name] = n
+	return n
+}
+
+// BlendedNoise builds the terrain blended noise, seeded from "minecraft:terrain".
+func (rs *RandomState) BlendedNoise(xzScale, yScale, xzFactor, yFactor, smear float64) *BlendedNoise {
+	return NewBlendedNoise(rs.factory.FromHashOf("minecraft:terrain"), xzScale, yScale, xzFactor, yFactor, smear)
+}