Add a high-latency server preset

[TaJirax]

What changed

• adds a server-only high-latency preset, with high_latency, highlatency, latency, and mobile accepted as aliases
• applyServerConfigPreset now validates against the server preset set, which already existed but was unused — it was checking the client list
• ships server_config.high-latency.toml alongside the other preset files

Why

Neither existing preset addresses round trip time. speed shortens the retransmit timeout to 0.5s, and survival leaves it at the 0.6s default while concentrating on FEC. On a mobile carrier with a 400ms base RTT and 100ms of jitter, both resend packets whose ACKs are still in flight; the duplicates add the delay that expires the next timer, and the tunnel degrades toward a standstill while reporting no loss at all. A 1000 packet window also cannot keep such a path full.

An operator running against Hamrahe Avval had already hand tuned a server for this, with # RTO tuned for 400ms base RTT + 100ms jitter and # NACK delays tuned for high latency (was 0.05s / 0.2s — WAY too aggressive) in their config. This preset is those findings, so the next operator does not have to rediscover them.

Values

Key	Default	Preset
ARQ_INITIAL_RTO_SECONDS	0.6	1.0
ARQ_MAX_RTO_SECONDS	3.0	4.0
ARQ_DATA_NACK_INITIAL_DELAY_SECONDS	0.4	0.3
ARQ_DATA_NACK_REPEAT_SECONDS	0.8	0.8
ARQ_DATA_NACK_MAX_GAP	64	64
ARQ_WINDOW_SIZE	1000	4096
MAX_PACKETS_PER_BATCH	10	32
MAX_DNS_RESPONSE_BYTES	32768	65535
UDP_READERS / DNS_REQUEST_WORKERS	cpu derived	16 / 16
MAX_CONCURRENT_REQUESTS	16384	32768
MAX_INGRESS_QUEUE_BYTES	64 MB	128 MB
SOCKET_BUFFER_SIZE	default	32 MB
DEFERRED_SESSION_WORKERS / _QUEUE_LIMIT	8 / 4096	16 / 16384

SESSION_TIMEOUT_SECONDS is deliberately not raised, even though the deployed config sets it to 1200. Holding abandoned sessions four times longer in a fixed size table is what makes a client that reconnects mid stall meet SESSION_BUSY and reconnect again.

Validation

• new test covers the applied values, that an explicit operator key still wins, that the aliases normalize, and that clients are not offered a server-only preset
• go build ./..., go vet ./..., and go test ./... pass

🤖 Generated with Claude Code