Add SSE client for web chat integration and enable event-based message handling.

- Introduced `SseSubscribeClient` to connect to the external web server and process events via SSE (Server-Sent Events).
- Added `WebHandler` interface for type-safe event deserialization and processing.
- Included `WebChatHandler` to handle incoming web chat messages and forward them to the chat system.
- Updated `Config` for new configurable values: `CHAT_WEB_REGISTER_TO_BASE_URL` and `CHAT_WEB_TOKEN`.

api/src/main/java/com/alttd/chat/config/Config.java

@@ -652,8 +652,12 @@ public final class Config {
     }
 
     public static String CHAT_WEB_SERVER_BASE_URL = "http://10.0.0.121:8080";
+    public static String CHAT_WEB_REGISTER_TO_BASE_URL = "https://alttd.com";
+    public static String CHAT_WEB_TOKEN = "invalid-token";
 
     private static void webServerSettings() {
         CHAT_WEB_SERVER_BASE_URL = getString("web-server.base-url", CHAT_WEB_SERVER_BASE_URL);
+        CHAT_WEB_REGISTER_TO_BASE_URL = getString("web-server.register-to-base-url", CHAT_WEB_REGISTER_TO_BASE_URL);
+        CHAT_WEB_TOKEN = getString("web-server.token", CHAT_WEB_TOKEN);
     }
 }

api/src/main/java/com/alttd/chat/web/SseSubscribeClient.java

@@ -0,0 +1,194 @@
+package com.alttd.chat.web;
+
+import com.alttd.chat.config.Config;
+import com.alttd.chat.util.ALogger;
+import com.fasterxml.jackson.databind.ObjectMapper;
+
+import java.io.BufferedReader;
+import java.io.InputStream;
+import java.io.InputStreamReader;
+import java.net.URI;
+import java.net.http.HttpClient;
+import java.net.http.HttpRequest;
+import java.net.http.HttpResponse;
+import java.nio.charset.StandardCharsets;
+import java.time.Duration;
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+
+/**
+ * Client for subscribing to: GET /api/chat/send/subscribe/{server} served as text/event-stream (SseEmitter) by
+ * CommandsToServerController.
+ * <p>
+ * Handlers for individual SSE event types can be registered up front via {@link #register(String, WebHandler)}. Each
+ * handler says "when an event named X arrives, deserialize its JSON payload as type T and pass it to this handler."
+ * Unregistered event names are logged and skipped, not thrown.
+ * <p>
+ * If the connection fails or drops for any reason, the client logs it and retries once a minute, indefinitely, until
+ * stop() is called or the thread is interrupted.
+ * <p>
+ * Server-side auth: the controller checks @AuthenticationPrincipal Token token, then token.getKey().equals(validToken).
+ * That principal is populated from the "Authorization: Bearer <token>" header. validToken is currently hardcoded
+ * server-side; swap TOKEN below for a config value once that TODO is resolved.
+ */
+public class SseSubscribeClient implements Runnable {
+
+    private static final Logger log = Logger.getLogger(SseSubscribeClient.class.getName());
+    private static final Duration RETRY_DELAY = Duration.ofMinutes(1);
+
+    private final String baseUrl;
+    private final String server;
+    private final HttpClient httpClient;
+    private final ObjectMapper objectMapper = new ObjectMapper();
+    private final Map<String, WebHandler<?>> handlers = new ConcurrentHashMap<>();
+
+    private volatile boolean running = false;
+
+    public SseSubscribeClient(String baseUrl, String server, String token) {
+        this.baseUrl = baseUrl;
+        this.server = server;
+        this.httpClient = HttpClient.newBuilder()
+                .connectTimeout(Duration.ofSeconds(10))
+                .build();
+    }
+
+    /**
+     * Register a handler for a given SSE event name. When an event with this name arrives, its data payload is
+     * deserialized using the handler's type and passed to the handler.
+     */
+    public <T> void register(String eventName, WebHandler<T> handler) {
+        handlers.put(eventName, handler);
+    }
+
+    /**
+     * Runs the subscribe/retry loop on the calling thread. Blocks until stop() is called or the thread is interrupted.
+     */
+    @Override
+    public void run() {
+        running = true;
+        while (running && !Thread.currentThread().isInterrupted()) {
+            String token = Config.CHAT_WEB_TOKEN;
+            if (token.equals("invalid-token")) {
+                log.warning("Invalid token provided for SSE connection as '" + server + "'");
+                sleepBeforeRetry();
+                continue;
+            }
+            try {
+                connectAndListen(token);
+                log.warning("SSE stream as '" + server + "' ended; reconnecting in " + RETRY_DELAY.toMinutes() + " minute(s)");
+            } catch (Exception e) {
+                log.log(Level.WARNING, "SSE connection to '" + server + "' failed; retrying in "
+                                       + RETRY_DELAY.toMinutes() + " minute(s)", e
+                );
+            }
+
+            if (running) {
+                sleepBeforeRetry();
+            }
+        }
+    }
+
+    public void stop() {
+        running = false;
+    }
+
+    private void connectAndListen(String token) throws Exception {
+        HttpResponse<InputStream> response = openConnection(token);
+        checkStatus(response);
+        readEvents(response.body());
+    }
+
+    private HttpResponse<InputStream> openConnection(String token) throws Exception {
+        HttpRequest request = HttpRequest.newBuilder()
+                .uri(URI.create(baseUrl + "/api/chat/server/send/subscribe/" + server))
+                .header("X-Altitude-Token", token)
+                .header("Accept", "text/event-stream")
+                .GET()
+                .build();
+
+        return httpClient.send(request, HttpResponse.BodyHandlers.ofInputStream());
+    }
+
+    private void checkStatus(HttpResponse<InputStream> response) {
+        int status = response.statusCode();
+        if (status == 401) {
+            throw new RuntimeException("Unauthorized - missing/invalid token");
+        }
+        if (status == 403) {
+            throw new RuntimeException("Forbidden - token did not match server's validToken");
+        }
+        if (status != 200) {
+            throw new RuntimeException("Unexpected status: " + status);
+        }
+        ALogger.info("SSE connection as '" + server + "' established");
+    }
+
+    /**
+     * Reads the SSE stream line by line, accumulating one event at a time, and dispatches each complete event as it's
+     * parsed.
+     */
+    private void readEvents(InputStream body) throws Exception {
+        try (BufferedReader reader = new BufferedReader(new InputStreamReader(body, StandardCharsets.UTF_8))) {
+            String eventName = null;
+            StringBuilder dataBuffer = new StringBuilder();
+            String line;
+
+            while ((line = reader.readLine()) != null) {
+                if (line.isEmpty()) {
+                    if (!dataBuffer.isEmpty()) {
+                        dispatch(eventName, dataBuffer.toString());
+                    }
+                    eventName = null;
+                    dataBuffer.setLength(0);
+                    continue;
+                }
+
+                if (line.startsWith("event:")) {
+                    eventName = line.substring(6).trim();
+                } else if (line.startsWith("data:")) {
+                    if (!dataBuffer.isEmpty()) {
+                        dataBuffer.append('\n');
+                    }
+                    dataBuffer.append(line.substring(5).trim());
+                }
+                // lines starting with ":" are comments/heartbeats - ignored
+            }
+        }
+    }
+
+    private void dispatch(String eventName, String data) {
+        if (eventName == null) {
+            log.warning("Received event with no 'event:' name, ignoring. Data: " + data);
+            return;
+        }
+
+        WebHandler<?> handler = handlers.get(eventName);
+        if (handler == null) {
+            log.warning("No handler registered for event type '" + eventName + "', ignoring");
+            return;
+        }
+
+        dispatchTyped(eventName, handler, data);
+    }
+
+    // Captures the wildcard type from the handler so parsing/casting is type-safe.
+    private <T> void dispatchTyped(String eventName, WebHandler<T> handler, String data) {
+        try {
+            T event = objectMapper.readValue(data, handler.type());
+            handler.handle(event);
+        } catch (Exception e) {
+            log.log(Level.WARNING, "Failed to parse/handle event '" + eventName + "'", e);
+        }
+    }
+
+    private void sleepBeforeRetry() {
+        try {
+            Thread.sleep(RETRY_DELAY.toMillis());
+        } catch (InterruptedException e) {
+            Thread.currentThread().interrupt();
+            running = false;
+        }
+    }
+}

api/src/main/java/com/alttd/chat/web/WebHandler.java

@@ -0,0 +1,9 @@
+package com.alttd.chat.web;
+
+public interface WebHandler<T> {
+
+    Class<T> type();
+
+    void handle(T event);
+
+}

api/src/main/java/com/alttd/chat/web/handler_class/ChatFromWeb.java

@@ -0,0 +1,15 @@
+package com.alttd.chat.web.handler_class;
+
+import lombok.Data;
+import lombok.NoArgsConstructor;
+
+import java.util.UUID;
+
+@Data
+@NoArgsConstructor
+public class ChatFromWeb {
+
+    private UUID sender;
+    private String message;
+
+}