Bolt-on multiplayer layer confined to src/native and hand-written code (no
codegen output touched):
- GhostRelay core (src/native/skate3_native_ghost_relay.*): small UDP relay
matching clients into rooms by a shareable code; forwards each client's
pose to the other room members. Used by both the standalone binary and
the in-game LAN host fallback.
- Standalone server (tools/ghost_relay_main.cpp, ghost_relay target): runs
on a public VPS or behind a free tunnel; clients connect OUTBOUND, so no
port forwarding is needed on any client.
- In-game module (skate3_native_ghost.*): captures the local player's world
transform at Sk8::UpdateBoneTransforms exit (pack-owner entity +416,
verified layout) and broadcasts it at a fixed rate; auto-connects to the
default public relay, falls back to LAN auto-host + UDP broadcast
discovery when unreachable.
- Renderer: draws a solid-color cube per remote player in RenderScene via
the existing scene PSO tint.a>0 branch (no new shader/SPIR-V).
- UI: GhostDialog (M key) with enable toggle, room code, relay override,
status readout. Off by default.
Wire protocol in skate3_native_ghost_proto.h (JOIN/HELLO/POSE/PING/LEAVE).
