c835996bd6
Three pure-ASGI middlewares close completeness-review gaps §3.1.4 (no body/rate limits) and §3.1.25 (no security headers): - BodySizeLimitMiddleware — rejects oversized uploads (50 MB default, CYCLONE_MAX_BODY_BYTES override). 413 on over-cap Content-Length and on chunked reads that cross the cap. - RateLimitMiddleware — sliding-window per-IP limiter (300/min default, CYCLONE_RATE_LIMIT_PER_MIN override). 429 over the window. /api/health is exempt. - SecurityHeadersMiddleware — stamps X-Content-Type-Options, X-Frame-Options, Referrer-Policy, Permissions-Policy, and a strict Content-Security-Policy on every response. Every 413/429 also writes a tamper-evident api.request_rejected event into the SP11 audit chain so an operator can correlate rejections with the SP18 JSON logs. GET /api/health is rewritten to return a subsystem snapshot: DB connectivity (SELECT 1), MFT scheduler state, backup scheduler state, live pubsub subscriber counts, last batch id + timestamp. Returns status='degraded' if any subsystem is unhappy; per-subsystem errors surfaced in the respective dict. Cyclone.pubsub.EventBus.stats() — new method for live subscriber counts. 13 new tests (test_security.py) + 1 updated (test_api.py health endpoint). All 883 backend tests pass.