Phase A of hard NAT traversal (PRD-hard-nat.md):
- PortAllocation enum: PortPreserving / Sequential{delta} / Random / Unknown
- detect_port_allocation(): sequential STUN probes from single socket,
analyzes port sequence for allocation pattern
- classify_port_allocation(): pure function with jitter tolerance,
wraparound handling, 60% threshold for noisy sequences
- predict_ports(): generates target port range from last_port + delta
- HardNatProbe signal message: carries port_sequence, allocation
pattern, external_ip for peer coordination
- Relay forwards HardNatProbe to call peer
- Netcheck gains port_allocation field + format_report display
588 tests pass (17 new), 0 regressions.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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