feat(chat): cut over to single SSE endpoint

src/main/java/com/superbiz/agent/controller/sse/SseEmitterChatSink.java

@@ -0,0 +1,28 @@
+package com.superbiz.agent.controller.sse;
+
+import org.springframework.http.MediaType;
+import org.springframework.web.servlet.mvc.method.annotation.SseEmitter;
+
+import java.io.IOException;
+import java.util.Objects;
+
+final class SseEmitterChatSink implements ChatSseSink {
+
+    private final SseEmitter emitter;
+
+    SseEmitterChatSink(SseEmitter emitter) {
+        this.emitter = Objects.requireNonNull(emitter, "emitter must not be null");
+    }
+
+    @Override
+    public void send(String name, Object payload) throws IOException {
+        emitter.send(SseEmitter.event()
+                .name(name)
+                .data(payload, MediaType.APPLICATION_JSON));
+    }
+
+    @Override
+    public void complete() {
+        emitter.complete();
+    }
+}