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/world/biome_lookup_test.go

@@ -0,0 +1,73 @@
+package world
+
+import (
+	"testing"
+
+	"regionio/internal/registry"
+	"regionio/internal/worldgen"
+)
+
+// TestBiomeAtDeterministic checks BiomeAt is stable for fixed seed/coords and
+// resolves to a registry-known biome (not a fallback placeholder).
+func TestBiomeAtDeterministic(t *testing.T) {
+	od, err := worldgen.LoadOverworldFinalDensity(12345)
+	if err != nil {
+		t.Fatalf("load: %v", err)
+	}
+	id1 := BiomeAt(od, 100, 200)
+	id2 := BiomeAt(od, 100, 200)
+	if id1 != id2 {
+		t.Fatalf("BiomeAt not deterministic: %d vs %d", id1, id2)
+	}
+	// The returned ID must be a valid registry biome, not the plains fallback by
+	// accident — resolve it back and confirm plains only when genuinely plains.
+	if int(id1) != registry.Index("minecraft:worldgen/biome", biomeName(od, 100, 200)) {
+		t.Errorf("BiomeAt id %d does not round-trip through registry", id1)
+	}
+}
+
+// biomeName is a test helper exposing the resolved biome name at (wx, wz).
+func biomeName(od *worldgen.OverworldDensity, wx, wz int) string {
+	point := worldgen.SampleColumn(od, SeaLevel, wx, wz)
+	return loadSurfaceTable().FindBiome(point)
+}
+
+// TestBiomeAtVaryingAcrossWorld confirms different regions of the world map to
+// different biomes — the whole point of multi-noise. If every sampled chunk
+// resolved to the same biome, climate sampling or the finder would be broken.
+func TestBiomeAtVaryingAcrossWorld(t *testing.T) {
+	od, err := worldgen.LoadOverworldFinalDensity(12345)
+	if err != nil {
+		t.Fatalf("load: %v", err)
+	}
+	seen := make(map[uint16]bool)
+	for cx := int32(0); cx < 16; cx++ {
+		for cz := int32(0); cz < 16; cz++ {
+			seen[BiomeAt(od, int(cx)*16+8, int(cz)*16+8)] = true
+		}
+	}
+	if len(seen) < 2 {
+		t.Fatalf("expected >=2 biomes across 16x16 chunks, got %d (%v)", len(seen), seen)
+	}
+	t.Logf("found %d distinct biomes across 16x16 chunks", len(seen))
+}
+
+// TestVanillaChunkHasBiome confirms generateVanilla threads the per-column biome
+// into the chunk (regression guard for the NewChunk call site in vanilla.go).
+func TestVanillaChunkHasBiome(t *testing.T) {
+	gen := NewVanillaGenerator(12345)
+	ch := gen(10, -3)
+	if ch == nil {
+		t.Fatal("nil chunk")
+	}
+	// biome is unexported; verify via the registry by re-deriving it. The chunk's
+	// biome must match what BiomeAt returns at the chunk centre.
+	od, err := worldgen.LoadOverworldFinalDensity(12345)
+	if err != nil {
+		t.Fatalf("load: %v", err)
+	}
+	want := BiomeAt(od, 10*16+8, -3*16+8)
+	if uint16(ch.biome) != want {
+		t.Errorf("chunk biome = %d, want %d", ch.biome, want)
+	}
+}