Implement in-experience (world/room) chat endpoints and pub/sub hook (US-4)

backend/app/services/chat_pubsub.py

@@ -0,0 +1,48 @@
+"""Pub/sub messaging bus for chat events over Redis.
+
+Provides asynchronous publish hooks for world/room chat and DMs, allowing the
+WebSocket real-time gateway (and multi-instance replicas) to receive and fan out
+chat messages in real time.
+"""
+
+from __future__ import annotations
+
+import json
+import logging
+from typing import Any
+
+import redis.asyncio as aioredis
+
+from app.config import settings
+
+logger = logging.getLogger(__name__)
+
+
+async def publish_world_chat_event(
+    world_id: int, payload: dict[str, Any], room_id: int | None = None
+) -> None:
+    """Publish a world chat message event to Redis pub/sub for real-time delivery."""
+    try:
+        client = aioredis.from_url(settings.REDIS_URL, encoding="utf-8", decode_responses=True)
+        async with client:
+            channel = f"world:{world_id}:chat"
+            data = json.dumps(payload, default=str)
+            await client.publish(channel, data)
+            if room_id is not None:
+                await client.publish(f"room:{room_id}:chat", data)
+    except Exception as exc:
+        logger.debug("Failed to publish world chat event to Redis: %s", exc)
+
+
+async def publish_dm_chat_event(
+    conversation_id: int, payload: dict[str, Any]
+) -> None:
+    """Publish a DM chat message event to Redis pub/sub for real-time delivery."""
+    try:
+        client = aioredis.from_url(settings.REDIS_URL, encoding="utf-8", decode_responses=True)
+        async with client:
+            channel = f"dm:{conversation_id}:chat"
+            data = json.dumps(payload, default=str)
+            await client.publish(channel, data)
+    except Exception as exc:
+        logger.debug("Failed to publish DM chat event to Redis: %s", exc)