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Wade Simmons
fb20de39b2
Lanes used to be separate HostInfos, each with its own handshake, its own half-established states, its own lifetime and its own slot bookkeeping. That bought nothing: a lane is the same tunnel over a different underlay 5-tuple. Derive lane sessions instead. Noise leaves us with A.eKey == B.dKey, so both sides HKDF-expand the same two keys with the same per-lane label and land on a matched pair without exchanging anything. Lanes now cost no handshake, have no half-established state, and die exactly when their base tunnel does. Which lane a packet belongs to rides the low byte of the nebula header's Reserved field, inside the AEAD's associated data. Receiving on a lane needs no permission, since the session exists the moment the base handshake completes. Sending on one needs proof the new 5-tuple works, so a lane stays down until a probe on it is acked and falls back to the base tunnel the moment it stops being acked. Probing is demand-driven off the connection manager's per-tunnel traffic tick: a peer we exchange a trickle with never costs more than its base tunnel, however many lanes are configured. The ack rides the base session on purpose, so a broken reverse lane can't fail a working one. Because the data now rides lane counters, the rehandshake, exhaustion and swap-primary checks take the max counter across the base session and its lanes; otherwise the base counter would sit near zero while a lane ran its keys past the nonce ceiling. Removes OutboundLaneTimer, EnsureLanes, startLaneHandshake, completeLane, completeLaneResponder, makeLaneTrafficDecision and the lane fields on HostInfo. Handshake payload field 3 (the per-lane handshake index) is permanently reserved; peers advertise a TxLanes count instead.