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/protocol/ids.go

@@ -0,0 +1,114 @@
+package protocol
+
+// Packet IDs, grouped by state and direction. Serverbound = client→server,
+// Clientbound = server→client. Values are for protocol 775 (26.1.2).
+
+// Handshaking, serverbound.
+const (
+	HandshakeID = 0x00
+)
+
+// Status, serverbound.
+const (
+	StatusRequestID = 0x00
+	PingRequestID   = 0x01
+)
+
+// Status, clientbound.
+const (
+	StatusResponseID = 0x00
+	PongResponseID   = 0x01
+)
+
+// Login, serverbound.
+const (
+	LoginStartID        = 0x00
+	EncryptionResponse  = 0x01
+	LoginPluginResponse = 0x02
+	LoginAcknowledgedID = 0x03
+	CookieResponseLogin = 0x04
+)
+
+// Login, clientbound.
+const (
+	LoginDisconnectID = 0x00
+	EncryptionRequest = 0x01
+	LoginSuccessID    = 0x02
+	SetCompressionID  = 0x03
+	LoginPluginReq    = 0x04
+	CookieRequestLogin = 0x05
+)
+
+// Configuration, serverbound.
+const (
+	ConfigClientInformation = 0x00
+	ConfigCookieResponse    = 0x01
+	ConfigCustomPayload     = 0x02
+	ConfigFinishServerbound = 0x03
+	ConfigKeepAliveServer   = 0x04
+	ConfigPong              = 0x05
+	ConfigResourcePackResp  = 0x06
+	ConfigKnownPacksServer  = 0x07
+)
+
+// Configuration, clientbound.
+const (
+	ConfigCookieRequest     = 0x00
+	ConfigCustomPayloadCB   = 0x01
+	ConfigDisconnect        = 0x02
+	ConfigFinishClientbound = 0x03
+	ConfigKeepAliveCB       = 0x04
+	ConfigPing              = 0x05
+	ConfigRegistryData          = 0x07
+	ConfigUpdateEnabledFeatures = 0x0c
+	ConfigUpdateTags            = 0x0d
+	ConfigKnownPacksCB          = 0x0e
+)
+
+// Play, clientbound (protocol 775).
+const (
+	PlayLogin            = 0x31
+	PlayGameEvent        = 0x26
+	PlayKeepAliveCB      = 0x2c
+	PlayPlayerPosition   = 0x48
+	PlayDefaultSpawnPos  = 0x61
+	PlayChunkCacheCenter = 0x5e
+	PlayLevelChunk       = 0x2d
+	PlayAbilities        = 0x40
+	PlaySetHeldSlot      = 0x69
+	PlayDisconnect       = 0x20
+	PlayBlockUpdate      = 0x08
+	PlayBlockChangedAck  = 0x04
+	PlaySystemChat       = 0x79
+)
+
+// Play, serverbound (protocol 775).
+const (
+	PlayAcceptTeleport     = 0x00
+	PlayKeepAliveServer    = 0x1c
+	PlayClientTickEnd      = 0x0d
+	PlayClientInformation  = 0x0e
+	PlayCustomPayload      = 0x16
+	PlayMovePos            = 0x1e
+	PlayMovePosRot         = 0x1f
+	PlayMoveRot            = 0x20
+	PlayMoveStatusOnly     = 0x21
+	PlayPlayerLoaded       = 0x2c
+	PlayPlayerAction       = 0x29
+	PlayUseItemOn          = 0x42
+	PlaySetCreativeSlot    = 0x38
+	PlaySetCarriedItem     = 0x35
+	PlayChatMessage        = 0x09
+)
+
+// GameEvent sub-IDs carried by the clientbound game_event packet.
+const (
+	GameEventStartWaitingChunks = 13
+)
+
+// NextState values carried by the handshake packet.
+const (
+	NextStateStatus   = 1
+	NextStateLogin    = 2
+	NextStateTransfer = 3
+)