D64 — Coupled pairs may twist at layer changes

Decision

Coupled pairs may twist at a layer change (on with pair routing); learned ordering and congestion models are not built

Alternatives

Twists off; a learned net-ordering model

Reason

Twists: 59 pairs, one gains coupling (0 → 86 %), none loses, median share 57 → 63 %. Ordering changes measured no effect on completion and tile congestion is absent (doc 05 §24, §25)