Add chat domain: models, service interfaces, and in-memory implementations

[Copilot]

Introduces a chat package implementing a Slack-inspired messaging concept with participants, chats, and messages — all backed by in-memory stores.

Models

• Participant — id, name, avatarUrl, role
• Chat — id, participantIds, messageIds, timestampCreated, metadata, lastSeenMessageIds
• Message — id, chatId, authorId, content, timestampSent
• PaginationOptions — page + size for message listing

Service interfaces + in-memory implementations

Interface	Implementation
ParticipantService	InMemoryParticipantService
ChatManagementService	InMemoryChatManagementService
MessagingService	InMemoryMessagingService

All stores use ConcurrentHashMap with UUID-assigned IDs. Services are wired as Spring @Service beans.

Participant alice = participantService.createParticipant("Alice", "https://…/alice.png", "admin");
Chat chat = chatManagementService.createChat(List.of(alice));

Message msg = new Message(null, null, alice.getId(), "Hello!", LocalDateTime.now());
messagingService.sendMessage(chat.getId(), msg);

List<Message> messages = messagingService.getMessages(chat.getId(), new PaginationOptions(0, 20));

Tests

30 @SpringBootTest integration tests across all three service implementations covering happy paths, pagination, and error cases.

Original prompt

start implementation

The user has attached the following files from their workspace:

• src/main/java/dev/rebelcraft/ai/spawn/chat/Participant.java
• slack.png

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.