Steam lobby: host, join, room, and launch into a marshaled race

RPL4LOBBY implements the multiplayer front door on ISteamMatchmaking.
The setup menu grows HOST STEAM RACE / JOIN STEAM RACE buttons when
the Steam wire is live; hosting creates a tagged public lobby, joining
finds one. Every member publishes FakeIP + fake ports + persona +
loadout as member data; the room screen lists members (host marked)
and gives the owner a launch button.

Launching writes a nonced go-roster into lobby data. Each pod
registers every peer with the Steam transport (two-port peer table:
engine console/game ports map to Steam fake ports on connect) and
enters the race: the owner through the hosted-race path - it builds
the multi-pilot egg from real personas and loadouts and its console
marshals everyone - and members as network pods that boot straight
into WaitingForEgg for the owner to feed over the wire.

The lobby outlives races: members loop back through WinMain into the
room (no local console needed - MissionCompleted is waived for member
races), and the owner returns to the room after its results screen.
Leaving the lobby clears the hosted-race priming.

Verified on this box: menu buttons appear under RP412STEAM=1, hosting
creates a lobby on the Steam backend, the room runs and leaves back to
the menu; single-player cycling and the LAN hosted race both still
pass. Full three-account mesh test is next, on real hardware.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

MUNGA_L4/L4STEAMTRANSPORT.cpp

@@ -58,9 +58,13 @@ namespace
 	struct PeerRecord
 	{
 		unsigned long		fakeIP;				// host order
+		unsigned short		fakeConsolePort;	// host order
 		unsigned short		fakeGamePort;		// host order
 	};
 
+	// engine-side port convention (lobby default; game port is +1)
+	unsigned short		gEngineConsolePort = 1501;
+
 	Logical				gSteamReady = False;
 	unsigned long		gLocalFakeIP = 0;		// host order
 	unsigned short		gLocalFakePorts[2] = { 0, 0 };
@@ -136,14 +140,17 @@ namespace
 		}
 	}
 
+	// engine port in a SOCKADDR_IN -> the peer's matching fake port
 	unsigned short
-		LookupPeerFakeGamePort(unsigned long fake_ip_host)
+		LookupPeerFakePort(unsigned long fake_ip_host, unsigned short engine_port)
 	{
 		for (int i = 0; i < gPeerCount; ++i)
 		{
 			if (gPeers[i].fakeIP == fake_ip_host)
 			{
-				return gPeers[i].fakeGamePort;
+				return (engine_port == gEngineConsolePort)
+					? gPeers[i].fakeConsolePort
+					: gPeers[i].fakeGamePort;
 			}
 		}
 		return 0;
@@ -272,8 +279,9 @@ namespace
 			)
 		{
 			unsigned long remote_fake_ip = ntohl(remote->sin_addr.S_un.S_addr);
-			unsigned short fake_game_port = LookupPeerFakeGamePort(remote_fake_ip);
-			if (fake_game_port == 0)
+			unsigned short fake_port =
+				LookupPeerFakePort(remote_fake_ip, ntohs(remote->sin_port));
+			if (fake_port == 0)
 			{
 				DEBUG_STREAM << "SteamNetTransport: no registered peer for "
 					<< inet_ntoa(remote->sin_addr) << " - lobby did not feed it\n" << std::flush;
@@ -281,8 +289,8 @@ namespace
 			}
 
 			DEBUG_STREAM << "SteamNetTransport: connecting to "
-				<< inet_ntoa(remote->sin_addr) << " (fake port "
-				<< fake_game_port << ")...\n" << std::flush;
+				<< inet_ntoa(remote->sin_addr) << ":" << ntohs(remote->sin_port)
+				<< " (fake port " << fake_port << ")...\n" << std::flush;
 
 			SteamNetworkingConfigValue_t option;
 			option.SetPtr(
@@ -291,7 +299,7 @@ namespace
 
 			SteamNetworkingIPAddr target;
 			target.Clear();
-			target.SetIPv4(remote_fake_ip, fake_game_port);
+			target.SetIPv4(remote_fake_ip, fake_port);
 
 			// mirror the TCP retry-while-refused loop, bounded: the
 			// egg-ACK ordering means the peer may not be listening yet
@@ -620,32 +628,56 @@ const char *
 	return gLocalFakeAddressString;
 }
 
+int
+	SteamNetTransport_GetFakeConsolePort()
+{
+	return gLocalFakePorts[0];
+}
+
 int
 	SteamNetTransport_GetFakeGamePort()
 {
 	return gLocalFakePorts[1];
 }
 
+void
+	SteamNetTransport_SetEnginePorts(int console_port)
+{
+	gEngineConsolePort = (unsigned short) console_port;
+}
+
 void
 	SteamNetTransport_RegisterPeer(
 		const char *fake_ip,
+		int fake_console_port,
 		int fake_game_port
 	)
 {
-	if (gPeerCount >= maxPeers)
-	{
-		return;
-	}
 	SteamNetworkingIPAddr parsed;
 	if (!parsed.ParseString(fake_ip))
 	{
 		return;
 	}
+	for (int i = 0; i < gPeerCount; ++i)
+	{
+		if (gPeers[i].fakeIP == parsed.GetIPv4())
+		{
+			gPeers[i].fakeConsolePort = (unsigned short) fake_console_port;
+			gPeers[i].fakeGamePort = (unsigned short) fake_game_port;
+			return;
+		}
+	}
+	if (gPeerCount >= maxPeers)
+	{
+		return;
+	}
 	gPeers[gPeerCount].fakeIP = parsed.GetIPv4();
+	gPeers[gPeerCount].fakeConsolePort = (unsigned short) fake_console_port;
 	gPeers[gPeerCount].fakeGamePort = (unsigned short) fake_game_port;
 	++gPeerCount;
 	DEBUG_STREAM << "SteamNetTransport: peer registered: " << fake_ip
-		<< " game port " << fake_game_port << "\n" << std::flush;
+		<< " (console " << fake_console_port << ", game "
+		<< fake_game_port << ")\n" << std::flush;
 }
 
 #endif	// RP412_STEAM

MUNGA_L4/L4STEAMTRANSPORT.h

@@ -68,15 +68,25 @@ Logical
 const char *
 	SteamNetTransport_GetFakeAddressString();
 
-// Our Steam-assigned fake game port (lobby member data).
+// Our Steam-assigned fake ports (lobby member data): the console
+// channel and the game mesh.
+int
+	SteamNetTransport_GetFakeConsolePort();
 int
 	SteamNetTransport_GetFakeGamePort();
 
-// The lobby feeds every member's FakeIP + fake game port here before
-// StartConnecting runs.
+// The engine-side port convention for this session (default 1501;
+// game port is +1). Connect() maps an engine port in a SOCKADDR_IN to
+// the peer's matching Steam fake port.
+void
+	SteamNetTransport_SetEnginePorts(int console_port);
+
+// The lobby feeds every member's FakeIP + fake ports here before
+// anything dials out. Registering is idempotent per IP.
 void
 	SteamNetTransport_RegisterPeer(
 		const char *fake_ip,
+		int fake_console_port,
 		int fake_game_port
 	);