M1: enforce the declared transfer size (clamped to MAX_SIZE) on chunk
receipt in both the Rust and Python clients — a malicious sender can no
longer grow the receive buffer unboundedly.
M2: only honor X-Forwarded-For when TRUST_PROXY is set, so a direct
client can't spoof a source IP to dodge the per-IP rate limiter.
M3: evict unverified SRP sessions after a 60s TTL on each new handshake,
preventing half-finished auths from exhausting memory.
M4: drop WS frames larger than 256 KB before they hit the store or
broadcast, bounding per-message memory and flood blast radius.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
