- Add _is_trusted_proxy() to check client IP against trusted CIDRs - Only use X-Forwarded-For if connection came from trusted proxy - Add TRUSTED_PROXY_CIDRS config (default: 127.0.0.1/32, ::1/128) - Add parse_comma_separated_lists for env var parsing - Add 3 unit tests: trusted CIDR check, untrusted ignores forwarded, trusted uses forwarded