Exchange construction/motion verification, 2026-09-14.

- cargo check --workspace --tests: passed, no warnings.
- cargo test -p ipu-codegen --release: 316 passed, 5 ignored; one doctest passed.
- Tests cover RAW/WAR/WAW copy hazards, aliases, strided overlap, idempotence,
  structured phase compaction, and compute/Repeat/checkpoint/provenance boundaries.
- Both 64-tile semantic fixtures passed hardware/reference checks:
  F16 MLP (Repeat 3) max abs 0.000183; modeled total 32613 / exchange 18087.
  FP8 ViT (3 layers, fused QKV) max abs 0.189453;
  modeled total 331874 / exchange 120708.
- Numerical results and modeled cycle counts are unchanged from product-family.

Commands, logs and binary profiles are adjacent. These small randomized fixtures
check semantics; they are not full-size trained-model performance measurements.