D49 — Opt-in min-cost-flow escape planning v2

Decision

Escape planning version 2 (min-cost-flow channel assignment on the pad layer, dog-bone sites by a second flow, then the same flow per further layer with the vias as obstacles; doc 05 §14) is opt-in (--escape-flow) and in no portfolio variant; one planning rule set per array (the most common class width/clearance/via), gap capacity from the narrower diagonal for all tracks

Alternatives

Replace version 1 in the two escape-plan variants; exact per-net capacities; Yan & Wong's separate per-diagonal accounting

Reason

One variant at fixed budgets on the 7 BGA-set boards with deep arrays: off 2,687, version 1 2,736, version 2 2,703 routed (better only on DoroidOscillo, +6 over version 1); narrower bands did not change that. A shared rule set keeps one power net from closing every channel; the narrower diagonal is conservative, so planned escapes always fit; the plan only reserves, so it cannot create violations (0 added KiCad errors on 3 outputs)