2V1-d: offline login -> select -> loading against a fake 40250 server

port.login_flow drives the real 40250 root scripts through the ported
CPythonNetworkStream and CAccountConnector against a loopback auth + game
server built from net/classic (wire layouts, sequence table, cipher) that
answers like the 40250 desc.cpp/input*.cpp: handshake, key agreement,
LOGIN3/AUTH_SUCCESS, LOGIN2, the character list, DirectEnter reconnect,
CHARACTER_SELECT, the loading packets and CLIENT_VERSION, with every
sequence byte checked.

- NetStream::ActivateCipher decrypts ciphertext already buffered behind
  KEY_AGREEMENT_COMPLETED (PORT)
- CPythonApplication is final (PORT): no application object exists on the
  platform yet, so its virtual overrides must be called directly
- app.GetTime (GetGlobalTime) and camera/center-position stubs
- SendClientVersionPacket verbatim in the PhaseGame stand-in

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

extension/tests/port_login_flow_server.h

@@ -0,0 +1,59 @@
+#pragma once
+// The server half of port_login_flow_test: a loopback auth server and game server that answer the way
+// the 40250 game server (game/src/desc.cpp, input.cpp, input_login.cpp, input_db.cpp) does for the
+// login → select → loading path. It is built from mtnet's classic wire layouts, sequence table and
+// cipher (net/classic/), which were checked 1:1 against the 40250 server on 192.168.21.203, and shares
+// no code with the ported client it talks to. Kept out of the client's translation unit: Packet.h's
+// macros collide with wire_classic.h's constants.
+#include <atomic>
+#include <cstdint>
+#include <mutex>
+#include <string>
+#include <thread>
+#include <vector>
+
+class FakeLoginServer
+{
+public:
+	static constexpr const char* kLogin = "fakeuser";
+	static constexpr const char* kPassword = "fakepass";
+	static constexpr const char* kCharacterName = "FakeWarrior";
+	static constexpr std::uint32_t kLoginKey = 0x13572468;
+	static constexpr std::uint32_t kMainVID = 0x00012345;
+	static constexpr std::int32_t kX = 469300, kY = 964200;
+
+	~FakeLoginServer();
+
+	// Listens on two loopback ports and serves them from a thread until Stop().
+	bool Start();
+	void Stop();
+
+	int AuthPort() const { return m_auth_port; }
+	int GamePort() const { return m_game_port; }
+
+	// Milestones in arrival order ("auth:login3", "game1:login2", ...), and the first protocol error.
+	std::vector<std::string> Events();
+	std::string Error();
+	bool Failed() { return !Error().empty(); }
+	bool Has(const std::string& event);
+
+	struct Connection;
+
+private:
+
+	void Run();
+	bool ServeAuth(Connection& c);
+	bool ServeGame(Connection& c, int index);
+	bool Handshake(Connection& c, std::uint8_t phase_after);
+	bool Accept(int listener, Connection& c);
+	void Event(const std::string& event);
+	bool Fail(const std::string& error);
+
+	int m_auth_listener = -1, m_game_listener = -1;
+	int m_auth_port = 0, m_game_port = 0;
+	std::thread m_thread;
+	std::atomic<bool> m_stop{false};
+	std::mutex m_mutex;
+	std::vector<std::string> m_events;
+	std::string m_error;
+};