Add local networking and test server

Introduce a localhost-only networking milestone and a tiny Python test server to verify packet flow from the plugin to an external process. Added F4T::Networking API (include and src) which uses non-blocking Winsock to connect to 127.0.0.1:7777, send JSON newline-separated transform packets, and handle reconnect/backoff and disconnects safely. Plugin changes: call ConnectToLocalServer() at load, register DisconnectFromLocalServer on exit, and send transform packets from main.cpp when logging player movement. Build: xmake updated to include new headers and link ws2_32. Server: server/server.py implements a simple multi-client TCP server that prints parsed transform packets; server/README.md and docs/dev-log.md updated to document the test setup and results. All networking failures are non-fatal so the game continues if the server isn't running.

server/README.md

@@ -2,19 +2,35 @@
 
 This folder is for the external multiplayer test server.
 
-The server is responsible for managing connected clients and broadcasting player state.
+The current server is a tiny local-only TCP test server. It listens on
+`127.0.0.1:7777`, accepts one or more clients, reads newline-separated JSON
+packets, and prints received player transform packets.
+
+## Run
+
+```bash
+cd server
+python server.py
+```
+
+Then launch Fallout 4 through F4SE and move the player. The plugin should keep
+logging player position changes to `Fallout4Together.log`, and this server
+should print matching `transform` packets.
+
+If the server is not running, the plugin should log a warning and Fallout 4
+should continue launching normally.
 
 ## First Server Goals
 
 - Start local server
 - Accept client connections
-- Assign player IDs
 - Receive transform packets
-- Broadcast transform packets
 - Handle disconnects
 
 ## Not Planned Yet
 
+- Remote actor spawning
+- Gameplay synchronization
 - Authentication
 - Public matchmaking
 - Anti-cheat

server/server.py

@@ -0,0 +1,100 @@
+from __future__ import annotations
+
+import json
+import socket
+import threading
+from typing import Any
+
+
+HOST = "127.0.0.1"
+PORT = 7777
+ACCEPT_TIMEOUT_SECONDS = 0.5
+
+
+def log(message: str) -> None:
+    print(message, flush=True)
+
+
+def handle_client(connection: socket.socket, address: tuple[str, int]) -> None:
+    client = f"{address[0]}:{address[1]}"
+    log(f"Client connected: {client}")
+
+    with connection:
+        buffer = ""
+
+        try:
+            while True:
+                chunk = connection.recv(4096)
+                if not chunk:
+                    break
+
+                buffer += chunk.decode("utf-8", errors="replace")
+                while "\n" in buffer:
+                    line, buffer = buffer.split("\n", 1)
+                    handle_line(client, line.strip())
+        except ConnectionResetError:
+            log(f"Client disconnected unexpectedly: {client}")
+        finally:
+            log(f"Client disconnected: {client}")
+
+
+def handle_line(client: str, line: str) -> None:
+    if not line:
+        return
+
+    try:
+        packet = json.loads(line)
+    except json.JSONDecodeError as error:
+        log(f"Invalid JSON from {client}: {error}: {line}")
+        return
+
+    print_packet(client, packet)
+
+
+def print_packet(client: str, packet: dict[str, Any]) -> None:
+    if packet.get("type") != "transform":
+        log(f"Packet from {client}: {packet}")
+        return
+
+    try:
+        x = float(packet["x"])
+        y = float(packet["y"])
+        z = float(packet["z"])
+        angle_z = float(packet["angleZ"])
+    except (KeyError, TypeError, ValueError):
+        log(f"Malformed transform packet from {client}: {packet}")
+        return
+
+    log(
+        "Transform from "
+        f"{client}: x={x:.2f}, y={y:.2f}, z={z:.2f}, angleZ={angle_z:.2f}"
+    )
+
+
+def main() -> None:
+    with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as server_socket:
+        if hasattr(socket, "SO_EXCLUSIVEADDRUSE"):
+            server_socket.setsockopt(socket.SOL_SOCKET, socket.SO_EXCLUSIVEADDRUSE, 1)
+        server_socket.bind((HOST, PORT))
+        server_socket.listen()
+        server_socket.settimeout(ACCEPT_TIMEOUT_SECONDS)
+
+        log(f"Fallout 4 Together local test server listening on {HOST}:{PORT}")
+        log("Waiting for newline-separated JSON transform packets...")
+
+        while True:
+            try:
+                connection, address = server_socket.accept()
+            except socket.timeout:
+                # Wake periodically so Ctrl+C is handled promptly in Windows terminals.
+                continue
+
+            thread = threading.Thread(target=handle_client, args=(connection, address), daemon=True)
+            thread.start()
+
+
+if __name__ == "__main__":
+    try:
+        main()
+    except KeyboardInterrupt:
+        log("\nServer stopped.")