Introduce uid.dat (offline PlayerUIDs), fix multiplayer save data persistence (#536)

* fix: fix multiplayer player data mix between different players bug

Fixes a Win64 multiplayer issue where player data (`players/*.dat`) could be mismatched because identity was effectively tied to connection-order `smallId` XUIDs.
Introduces a deterministic username-derived persistent XUID and integrates it into the existing XUID-based save pipeline.

- Added `Windows64_NameXuid` for deterministic `name -> persistent xuid` resolution
- On Win64 login (`PlayerList`), set `ServerPlayer::xuid` from username-based resolver
- Aligned local player `xuid` assignment (`Minecraft`) for create/init/respawn paths to use the same resolver
- Added Win64 local-self guard in `ClientConnection::handleAddPlayer` using name match to avoid duplicate local remote-player creation
- Kept `IQNet::GetPlayerByXuid` compatibility fallback behavior, while extending lookup to also resolve username-based XUIDs
- Moved implementation to `Minecraft.Client/Windows64/Windows64_NameXuid.h`; kept legacy `Win64NameXuid.h` as compatibility include

Rename migration is intentionally out of scope (same-name identity only).

* fix: preserve legacy host xuid (base xuid + 0) for existing world compatibility

- Add legacy embedded host XUID helper (base + 0).
- When Minecraft.Client is hosting, force only the first host player to use legacy host XUID.
- Keep name-based XUID for non-host players.
- Prevent old singleplayer/hosted worlds from losing/mismatching host player data.

* update: migrate Win64 player uid to `uid.dat`-backed XUID and add XUID based duplicate login guards

- Replace Win64 username-derived XUID resolution with persistent `uid.dat`-backed identity (`Windows64_Xuid` / `Win64Xuid`).
- Persist a per-client XUID next to the executable, with first-run generation, read/write, and process-local caching.
- Keep legacy host compatibility by pinning host self to legacy embedded `base + 0` XUID for existing world/playerdata continuity.
- Propagate packet-authoritative XUIDs into QNet player slots via `m_resolvedXuid`, and use it for `GetXuid`/`GetPlayerByXuid` with legacy fallback.
- Update Win64 profile/network paths to use persistent XUID for non-host clients and clear resolved identity on disconnect.
- Add login-time duplicate checks: reject connections when the same XUID is already connected (in addition to existing duplicate-name checks on Win64).
- Add inline compatibility comments around legacy/new identity coexistence paths for easier future maintenance.

* update: ensure uid.dat exists at startup in client mode for multiplayer

1 files changed, 39 insertions, 0 deletions

diff --git a/Minecraft.Client/Minecraft.cpp b/Minecraft.Client/Minecraft.cpp
index b87745f0..7ae206cf 100644
--- a/Minecraft.Client/Minecraft.cpp
+++ b/Minecraft.Client/Minecraft.cpp
@@ -52,6 +52,7 @@
 #include "..\Minecraft.World\net.minecraft.world.level.dimension.h"
 #include "..\Minecraft.World\net.minecraft.world.item.h"
 #include "..\Minecraft.World\Minecraft.World.h"
+#include "Windows64\Windows64_Xuid.h"
 #include "ClientConnection.h"
 #include "..\Minecraft.World\HellRandomLevelSource.h"
 #include "..\Minecraft.World\net.minecraft.world.entity.animal.h"
@@ -1038,6 +1039,19 @@ shared_ptr<MultiplayerLocalPlayer> Minecraft::createExtraLocalPlayer(int idx, co
 		PlayerUID playerXUIDOnline = INVALID_XUID;
 		ProfileManager.GetXUID(idx,&playerXUIDOffline,false);
 		ProfileManager.GetXUID(idx,&playerXUIDOnline,true);
+#ifdef _WINDOWS64
+		// Compatibility rule for Win64 id migration
+		// host keeps legacy host XUID, non-host uses persistent uid.dat XUID.
+		INetworkPlayer *localNetworkPlayer = g_NetworkManager.GetLocalPlayerByUserIndex(idx);
+		if(localNetworkPlayer != NULL && localNetworkPlayer->IsHost())
+		{
+			playerXUIDOffline = Win64Xuid::GetLegacyEmbeddedHostXuid();
+		}
+		else
+		{
+			playerXUIDOffline = Win64Xuid::ResolvePersistentXuid();
+		}
+#endif
 		localplayers[idx]->setXuid(playerXUIDOffline);
 		localplayers[idx]->setOnlineXuid(playerXUIDOnline);
 		localplayers[idx]->setIsGuest(ProfileManager.IsGuest(idx));
@@ -4299,6 +4313,19 @@ void Minecraft::setLevel(MultiPlayerLevel *level, int message /*=-1*/, shared_pt
 				playerXUIDOnline.setForAdhoc();
 			}
 #endif
+#ifdef _WINDOWS64
+			// On Windows, the implementation has been changed to use a per-client pseudo XUID based on `uid.dat`.  
+			// To maintain player data compatibility with existing worlds, the world host (the first player) will use the previous embedded pseudo XUID.
+			INetworkPlayer *localNetworkPlayer = g_NetworkManager.GetLocalPlayerByUserIndex(iPrimaryPlayer);
+			if(localNetworkPlayer != NULL && localNetworkPlayer->IsHost())
+			{
+				playerXUIDOffline = Win64Xuid::GetLegacyEmbeddedHostXuid();
+			}
+			else
+			{
+				playerXUIDOffline = Win64Xuid::ResolvePersistentXuid();
+			}
+#endif
 			player->setXuid(playerXUIDOffline);
 			player->setOnlineXuid(playerXUIDOnline);
 
@@ -4481,6 +4508,18 @@ void Minecraft::respawnPlayer(int iPad, int dimension, int newEntityId)
 	PlayerUID playerXUIDOnline = INVALID_XUID;
 	ProfileManager.GetXUID(iTempPad,&playerXUIDOffline,false);
 	ProfileManager.GetXUID(iTempPad,&playerXUIDOnline,true);
+#ifdef _WINDOWS64
+	// Same compatibility rule as create/init paths.
+	INetworkPlayer *localNetworkPlayer = g_NetworkManager.GetLocalPlayerByUserIndex(iTempPad);
+	if(localNetworkPlayer != NULL && localNetworkPlayer->IsHost())
+	{
+		playerXUIDOffline = Win64Xuid::GetLegacyEmbeddedHostXuid();
+	}
+	else
+	{
+		playerXUIDOffline = Win64Xuid::ResolvePersistentXuid();
+	}
+#endif
 	player->setXuid(playerXUIDOffline);
 	player->setOnlineXuid(playerXUIDOnline);
 	player->setIsGuest( ProfileManager.IsGuest(iTempPad) );