Extract common types for chat-store integration.

[jasperblues]

Extract Common Types for Chat-Store Integration

Summary

This PR introduces a new embabel-common-chat module containing storage-agnostic interfaces for chat/conversation persistence.
These common types enable both embabel-chat-store and embabel-agent to share a consistent contract without being directly coupled to each other.

Motivation

Previously, chat persistence types were tightly coupled to agent-specific abstractions (e.g., PromptContributor, Awaitable,
ActionContext). This made it difficult for embabel-chat-store to depend on conversation types without pulling in the entire
agent framework. By extracting minimal, persistence-focused interfaces into embabel-common, both modules can now share types through this common dependency.

Changes

New Module: embabel-common-chat
File: StorableConversation.kt
Description: Core interface for conversations with message management, slicing support, and persistence awareness
────────────────────────────────────────
File: StorableMessage.kt
Description: Minimal message interface with role, content, timestamp, and optional author/recipient
────────────────────────────────────────
File: MessageRole.kt
Description: Enum: USER, ASSISTANT, SYSTEM
────────────────────────────────────────
File: MessageAuthor.kt
Description: Interface for message author identity with id and displayName
────────────────────────────────────────
File: ConversationFactory.kt
Description: Factory interface for creating conversations, with ConversationStoreType enum (IN_MEMORY, STORED)
────────────────────────────────────────
File: ConversationFactoryProvider.kt
Description: Provider pattern for resolving factories by storage type
Simple Implementations Included:

• SimpleStorableMessage - Data class implementation for basic use cases
• SimpleMessageAuthor - Data class implementation for non-persistent scenarios
• MapConversationFactoryProvider - Map-based provider implementation

Architecture

  embabel-common-chat (this PR)
          ↑                ↑
          |                |
  embabel-agent    embabel-chat-store

Both downstream modules implement these interfaces:

• embabel-agent: Implements StorableConversation with rich agent context
• embabel-chat-store: Implements persistent storage (e.g., Neo4j-backed conversations)

[igordayen]

good approach

[igordayen]

what is relationship between MessageAuther and "User" from com.embabel.agent.api.identity

[alexheifetz]

Looks Good. Tnx!!