fix(transfer): use transferPlayer() beta API and enable experiments in level.dat

Switch from runCommand("transfer ...") to the @minecraft/server-admin
transferPlayer() function for reliable server-to-server transfers.
Enable Beta APIs experiment (gametest flag) in all 4 world level.dat files.
Add spawn protection to prevent transfer loops on arrival.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

scripts/enable-beta-apis.py

@@ -0,0 +1,108 @@
+#!/usr/bin/env python3
+"""
+Enable Beta APIs experiment in a Bedrock level.dat file.
+
+Bedrock level.dat format:
+  - 4 bytes: version (little-endian int32)
+  - 4 bytes: payload length (little-endian int32)
+  - rest: uncompressed little-endian NBT payload
+
+This script patches the 'experiments' compound tag to add:
+  - gametest = 1 (byte)
+  - experiments_ever_used = 1 (byte)
+  - saved_with_toggled_experiments = 1 (byte)
+
+Requires: amulet-nbt (pip install amulet-nbt)
+"""
+
+import struct
+import sys
+import shutil
+import amulet_nbt
+
+
+def patch_level_dat(path: str) -> None:
+    # Read the file
+    with open(path, "rb") as f:
+        header = f.read(8)
+        payload = f.read()
+
+    version, length = struct.unpack("<II", header)
+    print(f"  Header: version={version}, payload_length={length}")
+    print(f"  Actual payload size: {len(payload)}")
+
+    # Parse little-endian NBT (Bedrock format)
+    nbt = amulet_nbt.load(payload, little_endian=True)
+    root = nbt.compound
+
+    # Find experiments compound
+    if "experiments" not in root:
+        print("  ERROR: 'experiments' compound tag not found!")
+        sys.exit(1)
+
+    experiments = root["experiments"]
+    print(f"  Current experiments: {dict((k, v) for k, v in experiments.items())}")
+
+    changed = False
+
+    # Set flags to 1
+    for key in ("experiments_ever_used", "saved_with_toggled_experiments"):
+        if key in experiments:
+            if experiments[key].py_int == 0:
+                experiments[key] = amulet_nbt.ByteTag(1)
+                changed = True
+                print(f"  Set {key} = 1")
+        else:
+            experiments[key] = amulet_nbt.ByteTag(1)
+            changed = True
+            print(f"  Added {key} = 1")
+
+    # Add gametest experiment
+    if "gametest" not in experiments:
+        experiments["gametest"] = amulet_nbt.ByteTag(1)
+        changed = True
+        print("  Added gametest = 1")
+    elif experiments["gametest"].py_int == 0:
+        experiments["gametest"] = amulet_nbt.ByteTag(1)
+        changed = True
+        print("  Set gametest = 1")
+
+    if not changed:
+        print("  Already patched — no changes needed.")
+        return
+
+    # Serialize back (uncompressed, little-endian for Bedrock)
+    new_payload = nbt.save_to(little_endian=True, compressed=False)
+
+    # Build new header with updated length
+    new_header = struct.pack("<II", version, len(new_payload))
+
+    # Backup original
+    backup_path = path + ".bak"
+    shutil.copy2(path, backup_path)
+    print(f"  Backup saved to {backup_path}")
+
+    # Write patched file
+    with open(path, "wb") as f:
+        f.write(new_header)
+        f.write(new_payload)
+
+    print(f"  Patched! New payload size: {len(new_payload)}")
+
+
+def main():
+    if len(sys.argv) < 2:
+        print(f"Usage: {sys.argv[0]} <level.dat> [level.dat ...]")
+        sys.exit(1)
+
+    for path in sys.argv[1:]:
+        print(f"\nPatching: {path}")
+        patch_level_dat(path)
+
+    print("\nDone!")
+
+
+if __name__ == "__main__":
+    main()
+
+