feat(05-01): add round and message operations to discussion service

Add create_round, get_current_round, create_message, and get_round_messages
functions. All async with proper type hints and eager loading.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/moai/core/services/__init__.py

@@ -7,8 +7,12 @@ providing a clean interface for handlers to use.
 from moai.core.services.discussion import (
     complete_discussion,
     create_discussion,
+    create_message,
+    create_round,
     get_active_discussion,
+    get_current_round,
     get_discussion,
+    get_round_messages,
     list_discussions,
 )
 from moai.core.services.project import create_project, get_project, list_projects
@@ -16,10 +20,14 @@ from moai.core.services.project import create_project, get_project, list_project
 __all__ = [
     "complete_discussion",
     "create_discussion",
+    "create_message",
     "create_project",
+    "create_round",
     "get_active_discussion",
+    "get_current_round",
     "get_discussion",
     "get_project",
+    "get_round_messages",
     "list_discussions",
     "list_projects",
 ]

src/moai/core/services/discussion.py

@@ -11,7 +11,9 @@ from moai.core.models import (
     Discussion,
     DiscussionStatus,
     DiscussionType,
+    Message,
     Round,
+    RoundType,
 )
 
 
@@ -122,3 +124,96 @@ async def complete_discussion(discussion_id: str) -> Discussion | None:
         await session.flush()
         await session.refresh(discussion)
         return discussion
+
+
+async def create_round(
+    discussion_id: str,
+    round_number: int,
+    round_type: RoundType,
+) -> Round:
+    """Create a new round within a discussion.
+
+    Args:
+        discussion_id: The parent discussion's UUID.
+        round_number: Sequential round number within the discussion.
+        round_type: Whether this round is PARALLEL or SEQUENTIAL.
+
+    Returns:
+        The created Round object.
+    """
+    async with get_session() as session:
+        round_ = Round(
+            discussion_id=discussion_id,
+            round_number=round_number,
+            type=round_type,
+        )
+        session.add(round_)
+        await session.flush()
+        await session.refresh(round_)
+        return round_
+
+
+async def get_current_round(discussion_id: str) -> Round | None:
+    """Get the current (most recent) round for a discussion.
+
+    Args:
+        discussion_id: The discussion's UUID.
+
+    Returns:
+        The most recent Round object if found, None otherwise.
+    """
+    async with get_session() as session:
+        result = await session.execute(
+            select(Round)
+            .where(Round.discussion_id == discussion_id)
+            .order_by(Round.round_number.desc())
+            .limit(1)
+            .options(selectinload(Round.messages))
+        )
+        return result.scalar_one_or_none()
+
+
+async def create_message(
+    round_id: str,
+    model: str,
+    content: str,
+    is_direct: bool = False,
+) -> Message:
+    """Create a new message within a round.
+
+    Args:
+        round_id: The parent round's UUID.
+        model: AI model identifier (e.g., "claude", "gpt", "gemini").
+        content: The message content.
+        is_direct: True if this was a direct @mention to this model.
+
+    Returns:
+        The created Message object.
+    """
+    async with get_session() as session:
+        message = Message(
+            round_id=round_id,
+            model=model,
+            content=content,
+            is_direct=is_direct,
+        )
+        session.add(message)
+        await session.flush()
+        await session.refresh(message)
+        return message
+
+
+async def get_round_messages(round_id: str) -> list[Message]:
+    """Get all messages for a round ordered by timestamp.
+
+    Args:
+        round_id: The round's UUID.
+
+    Returns:
+        List of Message objects ordered by timestamp.
+    """
+    async with get_session() as session:
+        result = await session.execute(
+            select(Message).where(Message.round_id == round_id).order_by(Message.timestamp)
+        )
+        return list(result.scalars().all())