backend/app/middleware_setup.py

"""RMI Backend — middleware registration.

Per v3 unfuck rule #7: add_middleware MUST be called at module level,
NOT inside lifespan. FastAPI rejects middleware added after startup.

This module owns every middleware registration. Adding a new middleware:
  1. Add a `try_register(app, "name")` block below
  2. Each block is isolated — one failure doesn't break the rest
"""
from __future__ import annotations

import logging

log = logging.getLogger(__name__)


def register_middleware(app) -> None:
    """Register all middleware. Each registration is isolated."""
    _try_register_prometheus(app)
    _try_register_cost_tracking(app)
    _try_register_tracing(app)


def _try_register_prometheus(app) -> None:
    """Prometheus metrics middleware. Records every request."""
    try:
        from app.core.metrics import PrometheusMiddleware
        app.add_middleware(PrometheusMiddleware)
        log.info("middleware_registered name=prometheus")
    except Exception as exc:
        log.warning("middleware_skipped name=prometheus err=%s", exc)


def _try_register_cost_tracking(app) -> None:
    """M7 — per-tenant/per-route cost tracking."""
    try:
        from app.middleware.cost_tracking import CostTrackingMiddleware, CostBuffer
        app.add_middleware(CostTrackingMiddleware, buffer=CostBuffer())
        log.info("middleware_registered name=cost_tracking")
    except Exception as exc:
        log.warning("middleware_skipped name=cost_tracking err=%s", exc)


def _try_register_tracing(app) -> None:
    """Request-id + timing middleware (always on)."""
    try:
        from app.core.tracing import setup_tracing
        setup_tracing(app)
        log.info("middleware_registered name=tracing")
    except Exception as exc:
        log.warning("middleware_skipped name=tracing err=%s", exc)