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Johnathan Corgan
08a226fb63
The cost-selection chaos scenarios (cost-reeval, cost-avoidance, cost-stability, depth-vs-cost, mixed-technology, bottleneck-parent) tested TreeState::evaluate_parent's decision logic through a Docker mesh that could not exercise it reliably: the tree roots at whichever node holds the smallest NodeAddr, MMP link costs take several measurement windows to settle, and the parent hold-down plus hysteresis timing all confound the outcome. A deterministic link-cost flap still produced zero periodic parent switches in a full run. Replace those six scenarios with deterministic unit tests in src/tree/tests.rs that drive evaluate_parent directly: cheaper-link selection at equal depth, switch-on-cost-change, hysteresis suppressing a marginal change while allowing a significant one, and the depth-versus-cost effective-depth tradeoff. Each is constructed so that breaking the cost or hysteresis logic makes it fail. The congestion kernel-drop signal (SO_RXQ_OVFL) cannot be provoked deterministically in Docker: a fresh daemon reader keeps up with container-speed traffic, so the socket receive queue never overflows (an unshaped run with a 4 KB buffer and heavy traffic recorded zero drops on every node). Extract the drop-detection edge -- read the cumulative counter, fire an event only on the transition into a new drop burst -- into TransportDropState::observe_drops and unit-test it directly. congestion-stress keeps its ECN and MMP congestion-signal assertions, which do need the real shaped bottleneck queue. Remove the retired scenarios from both CI runners and update the chaos README.