feat(routing-policy): add experimental 'coupled' preset (MPTCP-style coupled congestion control) - #4113
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…coupled congestion control)
A new opt-in preset inspired by MPTCP's coupled congestion control (LIA/OLIA).
It provisions a modest symmetric mux (4) over the multi-hop overlay and weights
bytes toward the best legs (Distribution "auto"), then couples the aggregate in
on_tick using per-leg retransmit-delta (loss) and EWMA latency:
- coupled INCREASE (LIA-cautious): promote at most one warm spare per tick,
and only when NO active leg shows rising loss.
- coupled DECREASE: the instant any active leg's loss rises, shed the worst
leg (highest loss, latency-tiebroken; never leg 0, never below a floor of 2)
so aggregate aggressiveness stays bounded and traffic concentrates on the
good legs rather than equal-spreading across a lossy one.
Deterministic (no time.Now/rand) so the native and wazero paths stay
byte-identical. Registered in preset dispatch, names, and the bundle manifest;
bundle.wasm rebuilt. No existing default changes - decideAdaptive untouched.
Adds native unit tests (loss->shed-worst, clean->cautious-promote,
coupling-forbids-grow-under-loss) and coupled decide+tick cases to the
native<->wazero parity suite.
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Adds a new experimental routing-policy preset,
coupled, inspired by MPTCP'scoupled congestion control (LIA/OLIA). It is opt-in and changes no existing
default (
adaptiveand the shipped default are untouched).decidereturns a modest symmetric mux (4) over the multi-hop overlay and asksthe host to weight bytes toward the best legs (
Distribution: "auto"), ratherthan round-robin's equal spread across a congested leg. The
on_tickcontrollerthen couples the aggregate using two per-leg signals — the retransmit delta since
last tick (loss, packet-normalized by the sent-bytes delta) and EWMA latency:
only when NO active leg shows rising loss.
(highest loss, latency-tiebroken; never leg 0, never below a floor of 2), so
aggregate aggressiveness stays bounded and traffic concentrates on the good
legs.
The logic lives in the single source of truth (
pkg/router/policy/preset) and isdeterministic (no
time.Now/rand), so the native path and the recompiledbundle.wasmrun byte-identically. The bundle was rebuilt with TinyGo.Testing:
go test ./pkg/router/policy/...passes, including the native<->wazeroparity suite (decide + a multi-tick shed/promote sequence added for
coupled).New native unit tests cover loss->shed-worst, clean->cautious-promote, and the
coupling property that rising loss forbids growth even when a spare is available.