Carry painting across lobby/map respawns with isolated snapshot transfers

Persist each owner's paint snapshot on the MatchManager across the
despawn/respawn that happens on a lobby<->map scene switch, then reload
and rebroadcast it onto the freshly spawned avatar so painted meshes
survive the transition. Cleared on disconnect/shutdown to avoid stale
carry across sessions.

Isolate concurrent snapshot transfers by id so a respawning replica's
late-join request and the carry broadcast no longer share one reassembly
buffer (which decoded a mixed deflate blob -> "Corrupted data"), and drop
transfers with an older cutoff so a blank late-join cannot overwrite the
carried image.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Assets/Scripts/MatchManager.cs

@@ -97,6 +97,13 @@ public class MatchManager : MonoBehaviour
     // client every time. An independent System.Random decouples the pick from that shared global state.
     private readonly System.Random _roleRng = new System.Random(System.Guid.NewGuid().GetHashCode());
 
+    // Painting carry across an avatar respawn (scene switch). Per-machine: the LOCAL owner's painting,
+    // parked here by its despawning PlayerPaintSync (that component is gone before the replacement spawns)
+    // and consumed once by the next owner avatar. This manager is persistent in Main, so it bridges the
+    // despawn->spawn gap. Cleared on teardown (ReturnToMainOnly) so a fresh session never inherits a
+    // previous one's painting; a normal respawn keeps Main loaded, so the parked copy survives it.
+    private byte[] _carriedPaint;
+
     private void Awake()
     {
         if (Instance && Instance != this) { Destroy(this); return; }
@@ -381,6 +388,10 @@ public class MatchManager : MonoBehaviour
     // active gameplay scene is unloaded, otherwise Unity has no valid active scene to fall back to.
     private void ReturnToMainOnly()
     {
+        // A real disconnect/shutdown is not a respawn: drop any parked painting so a fresh session
+        // (re-host / reconnect) never restores a previous match's painting onto its first avatar.
+        _carriedPaint = null;
+
         Scene main = SceneManager.GetSceneByName(mainSceneName);
         if (main.IsValid() && main.isLoaded) SceneManager.SetActiveScene(main);
 
@@ -400,4 +411,15 @@ public class MatchManager : MonoBehaviour
         if (s.IsValid() && s.isLoaded && s != SceneManager.GetActiveScene())
             SceneManager.UnloadSceneAsync(s);
     }
+
+    /// <summary>Owner-side: park the local painting so the avatar a scene switch spawns next can restore it.</summary>
+    public void StoreCarriedPaint(byte[] data) => _carriedPaint = data;
+
+    /// <summary>Owner-side: take (and clear) the parked painting for the freshly spawned avatar, or null if none.</summary>
+    public byte[] TakeCarriedPaint()
+    {
+        byte[] d = _carriedPaint;
+        _carriedPaint = null;
+        return d;
+    }
 }