diff --git a/server/tests/test_networking_v2.py b/server/tests/test_networking_v2.py
new file mode 100644
index 0000000..92174ea
--- /dev/null
+++ b/server/tests/test_networking_v2.py
@@ -0,0 +1,150 @@
+from __future__ import annotations
+
+import json
+import socket
+import time
+
+import pytest
+
+from server_core import PROTOCOL_VERSION, FalloutTogetherServer, states_share_interest
+
+
+def recv_packet(sock: socket.socket, timeout: float = 2.0) -> dict:
+    sock.settimeout(timeout)
+    data = b""
+    while b"\n" not in data:
+        data += sock.recv(4096)
+    line, _ = data.split(b"\n", 1)
+    return json.loads(line.decode("utf-8"))
+
+
+def send_packet(sock: socket.socket, packet: dict) -> None:
+    sock.sendall(json.dumps(packet, separators=(",", ":")).encode() + b"\n")
+
+
+def connect(server: FalloutTogetherServer) -> tuple[socket.socket, dict]:
+    sock = socket.create_connection(("127.0.0.1", server.port), timeout=2.0)
+    return sock, recv_packet(sock)
+
+
+def hello(sock: socket.socket) -> dict:
+    send_packet(sock, {"type": "hello", "protocolVersion": PROTOCOL_VERSION})
+    return recv_packet(sock)
+
+
+def transform(cell: str, x: float, y: float, world: str = "0000003C") -> dict:
+    return {
+        "type": "transform",
+        "x": x,
+        "y": y,
+        "z": 0.0,
+        "angleZ": 0.0,
+        "cellId": cell,
+        "worldspaceId": world,
+    }
+
+
+def start_server(max_players: int = 16) -> FalloutTogetherServer:
+    server = FalloutTogetherServer(host="127.0.0.1", port=0, max_players=max_players)
+    server.start()
+    deadline = time.time() + 2
+    while not server.is_running() and time.time() < deadline:
+        time.sleep(0.01)
+    return server
+
+
+def test_interest_exact_cell_and_exterior_radius():
+    a = transform("00000001", 0, 0)
+    same = transform("00000001", 50000, 50000)
+    near = transform("00000002", 1000, 1000)
+    far = transform("00000002", 20000, 20000)
+    other_world = transform("00000002", 1000, 1000, world="0000003D")
+    assert states_share_interest(a, same)
+    assert states_share_interest(a, near)
+    assert not states_share_interest(a, far)
+    assert not states_share_interest(a, other_world)
+
+
+def test_idle_transport_does_not_take_world_authority():
+    server = start_server()
+    idle, _ = connect(server)
+    active, active_welcome = connect(server)
+    ready = hello(active)
+    assert ready["playerId"] == active_welcome["playerId"]
+    stats = server.get_stats()
+    assert stats["connectedClients"] == 1
+    assert stats["pendingConnections"] == 1
+    assert server._world_state_host_player_id == active_welcome["playerId"]
+    idle.close()
+    active.close()
+    server.stop()
+
+
+def test_max_players_applies_to_activated_sessions_not_probes():
+    server = start_server(max_players=1)
+    first, _ = connect(server)
+    hello(first)
+    second, _ = connect(server)
+    send_packet(second, {"type": "hello", "protocolVersion": PROTOCOL_VERSION})
+    ended = recv_packet(second)
+    assert ended["type"] == "sessionEnded"
+    assert ended["code"] == "server_full"
+    first.close()
+    second.close()
+    server.stop()
+
+
+def test_protocol_mismatch_is_rejected():
+    server = start_server()
+    sock, _ = connect(server)
+    send_packet(sock, {"type": "hello", "protocolVersion": PROTOCOL_VERSION + 1})
+    ended = recv_packet(sock)
+    assert ended["type"] == "sessionEnded"
+    assert ended["code"] == "protocol_mismatch"
+    sock.close()
+    server.stop()
+
+
+def test_nan_transform_is_rejected_and_not_cached():
+    server = start_server()
+    sock, welcome = connect(server)
+    hello(sock)
+    sock.sendall(
+        b'{"type":"transform","x":NaN,"y":0,"z":0,"angleZ":0,"cellId":"00000001"}\n'
+    )
+    time.sleep(0.05)
+    client = server._find_client_by_player_id(welcome["playerId"])
+    assert client is not None
+    assert client.last_transform is None
+    assert server.get_stats()["packetsRejected"] >= 1
+    sock.close()
+    server.stop()
+
+
+def test_transform_interest_filters_distant_peer():
+    server = start_server()
+    a, _ = connect(server)
+    hello(a)
+    b, _ = connect(server)
+    hello(b)
+    send_packet(b, transform("00000020", 25000, 25000))
+    time.sleep(0.05)
+    send_packet(a, transform("00000010", 0, 0))
+    b.settimeout(0.2)
+    with pytest.raises(socket.timeout):
+        b.recv(4096)
+    assert server.get_stats()["transformPacketsInterestFiltered"] >= 1
+    a.close()
+    b.close()
+    server.stop()
+
+
+def test_oversized_unterminated_packet_closes_session():
+    server = start_server()
+    sock, _ = connect(server)
+    sock.sendall(b"x" * (64 * 1024 + 1))
+    ended = recv_packet(sock)
+    assert ended["type"] == "sessionEnded"
+    assert ended["code"] == "packet_too_large"
+    sock.close()
+    server.stop()