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/MeshPainter.Net.cs

@@ -238,6 +238,31 @@ public partial class MeshPainter
         SetHistoryBaseline(canonical, baselineId);
     }
 
+    /// <summary>
+    /// Owner-side: re-seeds the painter from an in-memory snapshot blob and resets history to it as a fresh
+    /// local baseline - exactly like <see cref="LoadPaintByName"/> does for a file, just from bytes. Used to
+    /// carry a painting onto a freshly spawned avatar across a scene-switch respawn; the caller then
+    /// BroadcastLoadedPaint()s it to peers via the same path a manual load uses. Returns false if the painter
+    /// is not ready or the blob is missing / incompatible (the current painting is left untouched).
+    /// </summary>
+    public bool LoadPaintFromSnapshot(byte[] compressed)
+    {
+        if (!_setupValid || compressed == null || compressed.Length == 0) return false;
+
+        Color32[][] canonical;
+        try { canonical = DecodeSnapshot(compressed); }
+        catch (System.Exception e)
+        {
+            Debug.LogWarning($"[MeshPainter] Carry snapshot decode failed: {e.Message}", this);
+            return false;
+        }
+        if (canonical == null) return false;
+
+        ReseedCanonical(canonical);
+        ResetHistoryToCurrent(canonical);
+        return true;
+    }
+
     private Color32[][] DecodeSnapshot(byte[] compressed)
     {
         byte[] raw = Inflate(compressed);