Linux: sockets v013/v012 fallback + Steam lib docs

- SDK 1.65 provides GameServerNetworkingSockets v013, Skate DLL v012;
  try v013 then v012 (superset, same methods used)
- verified live: sign-in, Steam ID, join code, clean shutdown
- README: steamclient sdk64 symlink, version fallback note

Extension/Multiplayer/Steam/steam_transport.cpp

@@ -343,7 +343,17 @@ bool SteamTransport::open() {
         } catch (...) {
             p.friends = nullptr;
         }
-        return bind(module, symbol<void *(*)()>(module, "SteamAPI_SteamNetworkingSockets_SteamAPI_v012")(),
+        void *sockets = nullptr;
+        for (const char *name : {"SteamAPI_SteamNetworkingSockets_SteamAPI_v013",
+                                 "SteamAPI_SteamNetworkingSockets_SteamAPI_v012"}) {
+            try {
+                sockets = symbol<void *(*)()>(module, name)();
+                break;
+            } catch (...) {
+            }
+        }
+        if (!sockets) throw std::runtime_error("Missing Steam export: SteamAPI_SteamNetworkingSockets_SteamAPI");
+        return bind(module, sockets,
                     symbol<void *(*)()>(module, "SteamAPI_SteamNetworkingUtils_SteamAPI_v004")());
     } catch (const std::exception &e) {
         p.state.detail = e.what();
@@ -367,8 +377,19 @@ bool SteamTransport::open_game_server(void *library) {
         const auto find = symbol<void *(*)(int, const char *)>(module, "SteamInternal_FindOrCreateGameServerInterface");
         // Game servers have no friends list; names come from each player's hello.
         p.friends = nullptr;
-        return bind(module, symbol<void *(*)()>(module, "SteamAPI_SteamGameServerNetworkingSockets_SteamAPI_v012")(),
-                    find(user, "SteamNetworkingUtils004"));
+        // Sockets v012 (Skate's Windows DLL) vs v013 (current SDK): same methods
+        // used here, v013 is a superset. Try new first, fall back to old.
+        void *sockets = nullptr;
+        for (const char *name : {"SteamAPI_SteamGameServerNetworkingSockets_SteamAPI_v013",
+                                 "SteamAPI_SteamGameServerNetworkingSockets_SteamAPI_v012"}) {
+            try {
+                sockets = symbol<void *(*)()>(module, name)();
+                break;
+            } catch (...) {
+            }
+        }
+        if (!sockets) throw std::runtime_error("Missing Steam export: SteamAPI_SteamGameServerNetworkingSockets_SteamAPI");
+        return bind(module, sockets, find(user, "SteamNetworkingUtils004"));
     } catch (const std::exception &e) {
         p.state.detail = e.what();
         return false;

Server/README-linux.md

@@ -18,7 +18,8 @@ the release ZIP is expected to ship them; this repo never vendors Valve binaries
 
 - `libsteam_api.so`: from the Steamworks SDK `redistributable_bin/linux64/`
   (official download via `partner.steamgames.com`; any recent 1.x works — the server
-  uses stable flat exports `SteamGameServer015`/`SteamNetworkingSockets012`).
+  tries `SteamGameServerNetworkingSockets_SteamAPI_v013` then `v012`, and uses
+  stable flat exports `SteamGameServer015`/`SteamNetworkingUtils004`).
   It is generic; the app is selected at runtime via `SteamAppId=3354750`.
 - `steamclient.so` (+ `tier0`/`vstdlib` if present): **not** in the SDK.
   Get it from SteamCMD or a Steam client install, e.g.:
@@ -28,8 +29,9 @@ the release ZIP is expected to ship them; this repo never vendors Valve binaries
   # next to ReSkateServer (same folder as libsteam_api.so)
   ```
   or copy/symlink an existing client copy (`~/.steam/steam/linux64/steamclient.so`,
-  Valve also documents `~/.steam/sdk64/steamclient.so`). The server `dlopen`s
-  `libsteam_api.so`, which in turn loads `steamclient.so`; either adjacent or
+  Valve also documents `~/.steam/sdk64/steamclient.so` — the server looks there,
+  so `ln -s <folder>/steamclient.so ~/.steam/sdk64/steamclient.so` works).
+  The server `dlopen`s `libsteam_api.so`, which in turn loads `steamclient.so`; either adjacent or
   `LD_LIBRARY_PATH` works.
 
 Arch/CachyOS: