- Call rooms (call-*) restricted to the two authorized participants only
- Room capacity enforced at 2 for call rooms
- Unauthorized clients get immediate connection close
- Unified fingerprint format: SHA-256(Ed25519 pub)[:16] as xxxx:xxxx:...
Used consistently in signal registration, handshake, and ACL checks
Tested: Alice+Bob authorized, attacker rejected with "not authorized"
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>