Every route starts and ends with a stub from the pin to its first grid
cell, and the grid never saw that copper: on the rc4 sense board 24 of 39
connections the exact verifier rejected had a later route pass beside an
earlier stub. A route's stubs now claim the cells they come near, a stub
must be clear of other nets to be used, and a route may start from any
enterable neighbour of the pin cell, costed by stub length (Manhattan on
the orthogonal track, so a pin on a cell centre still leaves straight).
Tests: a route near a rounded corner keeps its edge clearance; and a
strict xfail that pins down the remaining gap, a 0.5 mm pin row the grid
cannot give a column to every pin of.
rsp2k
9fa5432953