Initial commit: standalone Pyxis T-Deck firmware

Split T-Deck firmware from microReticulum examples/lxmf_tdeck/ into its
own repo. microReticulum is consumed as a git submodule dependency pinned
to feat/t-deck. All include paths updated from relative symlinks to bare
includes resolved via library build flags.

Both tdeck (NimBLE) and tdeck-bluedroid environments compile successfully.
Licensed under AGPLv3.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/TCPClientInterface.h

@@ -0,0 +1,124 @@
+#pragma once
+
+#include "Interface.h"
+#include "Bytes.h"
+#include "Type.h"
+
+#ifdef ARDUINO
+#include <WiFi.h>
+#include <WiFiClient.h>
+#else
+#include <netinet/in.h>
+#endif
+
+#include <stdint.h>
+#include <string>
+
+#define DEFAULT_TCP_PORT 4965
+
+/**
+ * TCPClientInterface - TCP client interface for microReticulum.
+ *
+ * Connects to a Python RNS TCPServerInterface or another TCP server.
+ * Uses HDLC framing for wire protocol compatibility with Python RNS.
+ *
+ * Features:
+ * - Automatic reconnection with configurable retry interval
+ * - TCP keepalive for connection health monitoring
+ * - HDLC framing (0x7E flags with byte stuffing)
+ *
+ * Usage:
+ *   TCPClientInterface* tcp = new TCPClientInterface("tcp0");
+ *   tcp->set_target_host("192.168.1.100");
+ *   tcp->set_target_port(4965);
+ *   Interface interface(tcp);
+ *   interface.start();
+ *   Transport::register_interface(interface);
+ */
+class TCPClientInterface : public RNS::InterfaceImpl {
+
+public:
+    // Match Python RNS constants
+    static const uint32_t BITRATE_GUESS = 10 * 1000 * 1000;  // 10 Mbps
+    static const uint32_t HW_MTU = 1064;  // Match UDPInterface
+
+    // Reconnection parameters (match Python RNS)
+    static const uint32_t RECONNECT_WAIT_MS = 5000;  // 5 seconds between reconnect attempts
+    static const uint32_t CONNECT_TIMEOUT_MS = 5000; // 5 second connection timeout
+
+    // TCP keepalive parameters (match Python RNS)
+    static const int TCP_KEEPIDLE_SEC = 5;
+    static const int TCP_KEEPINTVL_SEC = 2;
+    static const int TCP_KEEPCNT_PROBES = 12;
+
+public:
+    TCPClientInterface(const char* name = "TCPClient");
+    virtual ~TCPClientInterface();
+
+    // Configuration (call before start())
+    void set_target_host(const std::string& host) { _target_host = host; }
+    void set_target_port(int port) { _target_port = port; }
+
+    // InterfaceImpl overrides
+    virtual bool start();
+    virtual void stop();
+    virtual void loop();
+
+    virtual inline std::string toString() const {
+        return "TCPClientInterface[" + _name + "/" + _target_host + ":" + std::to_string(_target_port) + "]";
+    }
+
+protected:
+    virtual void send_outgoing(const RNS::Bytes& data);
+
+private:
+    // Connection management
+    bool connect();
+    void disconnect();
+    void configure_socket();
+    void handle_disconnect();
+
+    // HDLC frame processing
+    void process_incoming();
+    void extract_and_process_frames();
+
+    // Target server
+    std::string _target_host;
+    int _target_port = DEFAULT_TCP_PORT;
+
+    // Connection state
+    bool _initiator = true;
+    uint32_t _last_connect_attempt = 0;
+    bool _reconnected = false;  // Set when connection re-established after being offline
+    uint32_t _last_data_received = 0;  // Track last data receipt for stale connection detection
+    static const uint32_t STALE_CONNECTION_MS = 120000;  // Consider connection stale after 2 min no data
+
+public:
+    // Check and clear reconnection flag (for announcing after reconnect)
+    bool check_reconnected() {
+        if (_reconnected) {
+            _reconnected = false;
+            return true;
+        }
+        return false;
+    }
+
+private:
+
+    // HDLC frame buffer for partial frame reassembly
+    RNS::Bytes _frame_buffer;
+
+    // Read buffer for incoming data
+    RNS::Bytes _read_buffer;
+
+    // Platform-specific socket
+#ifdef ARDUINO
+    WiFiClient _client;
+    // WiFi credentials (for ESP32 WiFi connection)
+    std::string _wifi_ssid;
+    std::string _wifi_password;
+#else
+    int _socket = -1;
+    in_addr_t _target_address = INADDR_NONE;
+#endif
+};