feat(chat): auto-generate titles for chat sessions

src/main/java/ai/decompile/ai/controller/ChatController.java

@@ -143,6 +143,8 @@ public class ChatController {
                   oldName,
                   "newName",
                   (Object) newName);
+          case StreamEvent.TitleGenerated(var title, var sessionId) ->
+              Map.of("type", "title_generated", "title", title, "sessionId", sessionId);
         };
     return ServerSentEvent.<String>builder().data(toJson(data)).build();
   }

src/main/java/ai/decompile/ai/model/dto/StreamEvent.java

@@ -10,7 +10,8 @@ public sealed interface StreamEvent
         StreamEvent.Done,
         StreamEvent.Error,
         StreamEvent.RenameSuggestion,
-        StreamEvent.FunctionRenamed {
+        StreamEvent.FunctionRenamed,
+        StreamEvent.TitleGenerated {
 
   record Chunk(String content) implements StreamEvent {}
 
@@ -28,4 +29,6 @@ public sealed interface StreamEvent
       implements StreamEvent {}
 
   record FunctionRenamed(UUID functionId, String oldName, String newName) implements StreamEvent {}
+
+  record TitleGenerated(String title, UUID sessionId) implements StreamEvent {}
 }

src/main/java/ai/decompile/ai/service/ChatService.java

@@ -21,6 +21,7 @@ import lombok.extern.log4j.Log4j2;
 import org.jspecify.annotations.NonNull;
 import org.springframework.ai.chat.client.ChatClient;
 import org.springframework.ai.chat.messages.Message;
+import org.springframework.ai.chat.messages.UserMessage;
 import org.springframework.ai.chat.model.ChatModel;
 import org.springframework.ai.chat.prompt.Prompt;
 import org.springframework.ai.support.ToolCallbacks;
@@ -86,6 +87,12 @@ public class ChatService {
                   () -> {
                     log.debug("Chat completed for session {}", sessionId);
                     saveAssistantMessage(session, assistantContent.toString());
+                    generateAndSetTitle(
+                        session,
+                        chatModel,
+                        request.content(),
+                        assistantContent.toString(),
+                        eventSink);
                     eventSink.tryEmitComplete();
                   })
               .doOnError(
@@ -131,6 +138,52 @@ public class ChatService {
     }
   }
 
+  private void generateAndSetTitle(
+      ChatSession session,
+      ChatModel chatModel,
+      String userMessage,
+      String assistantResponse,
+      Sinks.Many<StreamEvent> eventSink) {
+
+    if (Objects.isNull(session.getTitle()) || !session.getTitle().endsWith(" — Chat")) {
+      return;
+    }
+
+    try {
+      var truncatedResponse = AiUtils.truncate(assistantResponse, 500);
+      var prompt =
+          String.format(
+              """
+              Generate a very short title for a chat conversation
+              (maximum 6 words, 50 characters). Output ONLY the title text.
+              No quotes, no punctuation, no explanation.
+
+              User message: %s
+
+              Assistant response: %s
+
+              Title:""",
+              userMessage, truncatedResponse);
+
+      var response = chatModel.call(new Prompt(new UserMessage(prompt)));
+      var title = response.getResult().getOutput().getText();
+
+      if (Objects.nonNull(title) && !title.isBlank()) {
+        title = title.trim().replaceAll("^[\"'\\[\\]]+|[\"'\\[\\]]+$", "");
+
+        if (title.length() > 50) {
+          title = title.substring(0, 50);
+        }
+
+        sessionService.updateTitle(session.getId(), title);
+        eventSink.tryEmitNext(new StreamEvent.TitleGenerated(title, session.getId()));
+        log.info("Auto-generated title '{}' for session {}", title, session.getId());
+      }
+    } catch (Exception e) {
+      log.warn("Failed to auto-generate title for session {}: {}", session.getId(), e.getMessage());
+    }
+  }
+
   private class ObservedToolCallback implements ToolCallback {
     private final ToolCallback delegate;
     private final Sinks.Many<StreamEvent> eventSink;

src/main/java/ai/decompile/ai/service/ChatSessionService.java

@@ -96,4 +96,16 @@ public class ChatSessionService {
 
     messageRepository.save(msg);
   }
+
+  @Transactional(propagation = Propagation.REQUIRES_NEW)
+  public void updateTitle(UUID sessionId, String title) {
+    var session =
+        sessionRepository
+            .findById(sessionId)
+            .orElseThrow(
+                () -> new NotFoundException("Chat session with id '" + sessionId + "' not found"));
+
+    session.setTitle(title);
+    sessionRepository.save(session);
+  }
 }