bug: fallback DM message leaks '[AI model not configured]' prefix to players

[Sealjay]

Summary

When Azure OpenAI is unavailable, the POST /game/input endpoint returns a message with a visible [AI model not configured] prefix directly to players:

{"message": "[AI model not configured] You continue your journey."}

This technical error marker is never stripped before the response is returned to the frontend, and would be shown verbatim in the game chat interface. Players see the system's internal configuration state rather than a graceful 'service unavailable' message.

Expected Behaviour

Either:

1. Return HTTP 503 with {"detail": "AI service unavailable"} so the frontend can show a user-friendly error, OR
2. Return a clearly flagged fallback that the frontend suppresses and replaces with a toast/banner

Actual Behaviour

HTTP 200 with raw [AI model not configured] in the player-visible message field.

Files

• backend/app/agents/dungeon_master_agent.py — fallback response generation
• frontend/src/components/GameInterface.tsx — no filtering of fallback messages

Related

• bug: Azure OpenAI not configured — all AI agent features return stubs in dev environment #714 — Azure OpenAI unconfigured