Compose OpenAI Secure MCP Tunnel adapter diagnostics for tenant_id, alongside Meridian's own tunnel socket state (see :func:tunnel_status).

Body (all optional): {"openai_tunnel_config": {...}, "reported_status": {...}}. openai_tunnel_config is validated via openai_tunnel_adapter.normalize_config — a malformed config yields a 400 with the validation error, never a partial/best-guess diagnostics response. reported_status optionally carries a live {"state": ..., "detail": ...} health report from wherever actually probes the OpenAI tunnel (out of scope for this item; see the adapter module's docstring). Omitting both reports not_configured — no auth required, mirroring :func:tunnel_status's own lightweight, read-only status check.