From 32c5e438eda8abf286c2bd444225751576013e66 Mon Sep 17 00:00:00 2001
From: MiTHRAL <mithral@mithral.local>
Date: Wed, 26 Aug 2026 23:17:08 -0400
Subject: [PATCH] ghost multiplayer: fix wire-struct packing; set default relay
 to relay.mithraic.lol

- #pragma pack(1) on all protocol structs: alignas(1) set the struct
  alignment but still let the compiler pad members to their natural
  alignment - the uint16_t payload_size landed on an even offset, so
  PacketHeader was 8 bytes instead of 7 and the relay's
   guard dropped every real 7-byte packet
  (n=7 < 8). The in-process tests passed only because BuildPacket/PacketSize
  used the same inflated size on both sides. With true packing the struct
  sizes now equal the wire sizes exactly (PacketHeader=7, PosePayload=3140,
  HelloPayload=687, RoomsPayload=1266, ...), verified.
- kGhostDefaultServer -> relay.mithraic.lol (the production beta relay on
  the OVH VPS; IPv6 PTR set, IPv4 PTR still pending at OVH).
---
 src/native/skate3_native_ghost_proto.h | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/src/native/skate3_native_ghost_proto.h b/src/native/skate3_native_ghost_proto.h
index c63bad0..b9f61b8 100644
--- a/src/native/skate3_native_ghost_proto.h
+++ b/src/native/skate3_native_ghost_proto.h
@@ -35,8 +35,10 @@ constexpr uint32_t kGhostMaxRoomMembers = 4;   // member names shown per room
 // captured count are identity-padded so every mesh's referenced bones stay
 // in range on the receiving side.
 constexpr uint32_t kGhostMaxBones = 64;
-// Placeholder default public relay: replace in ONE place (skate3_native_ghost.cpp).
-constexpr const char* kGhostDefaultServer = "ghost.skate3.example";
+// Default public relay (the production beta relay on the OVH VPS). Clients
+// connect OUTBOUND to this; no port forwarding on any client. Override at
+// runtime with skate3_ghost_server.
+constexpr const char* kGhostDefaultServer = "relay.mithraic.lol";
 constexpr uint16_t kGhostDefaultServerPort = 40001;
 // A LAN host with no room advertised is implicitly in this room.
 constexpr const char* kGhostLobbyRoom = "LOBBY";
@@ -53,7 +55,15 @@ enum PacketType : uint8_t {
   kTypeRooms = 9,  // relay -> client: { RoomsPayload } (the lobby browser)
 };
 
-struct alignas(1) PacketHeader {
+// True byte-packing: the struct layouts below must match the wire format
+// exactly (the receiver bounds-checks every packet against these sizes, and
+// the relay rejects undersized datagrams with `n < sizeof(PacketHeader)`).
+// alignas(1) alone is NOT enough - it sets the struct alignment but the
+// compiler still pads MEMBERS to their natural alignment (a uint16_t lands
+// on an even offset, inflating PacketHeader to 8 bytes and dropping every
+// real 7-byte packet).
+#pragma pack(push, 1)
+struct PacketHeader {
   uint32_t magic;
   uint8_t type;
   uint16_t payload_size;  // bytes following this header
@@ -201,10 +211,11 @@ struct GhostPoseReassembler {
 // Largest payload: PoseChunkPayload (1214 bytes).
 constexpr uint16_t kGhostMaxPayload = 3200;
 
-struct alignas(1) PacketBuf {
+struct PacketBuf {
   PacketHeader h;
   uint8_t payload[kGhostMaxPayload];
 };
+#pragma pack(pop)
 
 inline uint16_t PacketSize(const PacketBuf& p) {
   return uint16_t(sizeof(PacketHeader) + p.h.payload_size);